Chapter 6 MySQL Server Administration

Table of Contents

6.1 The MySQL Server
6.1.1 Configuring the Server
6.1.2 Server Configuration Defaults
6.1.3 Server Option and Variable Reference
6.1.4 Server Command Options
6.1.5 Server System Variables
6.1.6 Using System Variables
6.1.7 Server Status Variables
6.1.8 Server SQL Modes
6.1.9 IPv6 Support
6.1.10 Server-Side Help
6.1.11 Server Response to Signals
6.1.12 The Server Shutdown Process
6.2 The MySQL Data Directory
6.3 The mysql System Database
6.4 MySQL Server Logs
6.4.1 Selecting General Query and Slow Query Log Output Destinations
6.4.2 The Error Log
6.4.3 The General Query Log
6.4.4 The Binary Log
6.4.5 The Slow Query Log
6.4.6 The DDL Log
6.4.7 Server Log Maintenance
6.5 MySQL Server Plugins
6.5.1 Server Plugins Available
6.5.2 Installing and Uninstalling Plugins
6.5.3 Obtaining Server Plugin Information
6.5.4 MySQL Enterprise Thread Pool
6.5.5 The Rewriter Query Rewrite Plugin
6.5.6 Version Tokens
6.6 Running Multiple MySQL Instances on One Machine
6.6.1 Setting Up Multiple Data Directories
6.6.2 Running Multiple MySQL Instances on Windows
6.6.3 Running Multiple MySQL Instances on Unix
6.6.4 Using Client Programs in a Multiple-Server Environment
6.7 Tracing mysqld Using DTrace
6.7.1 mysqld DTrace Probe Reference

MySQL Server (mysqld) is the main program that does most of the work in a MySQL installation. This chapter provides an overview of MySQL Server and covers general server administration:

For additional information on administrative topics, see also:

6.1 The MySQL Server

mysqld is the MySQL server. The following discussion covers these MySQL server configuration topics:

  • Startup options that the server supports. You can specify these options on the command line, through configuration files, or both.

  • Server system variables. These variables reflect the current state and values of the startup options, some of which can be modified while the server is running.

  • Server status variables. These variables contain counters and statistics about runtime operation.

  • How to set the server SQL mode. This setting modifies certain aspects of SQL syntax and semantics, for example for compatibility with code from other database systems, or to control the error handling for particular situations.

  • The server shutdown process. There are performance and reliability considerations depending on the type of table (transactional or nontransactional) and whether you use replication.

For listings of MySQL server variables and options that have been added, deprecated, or removed in MySQL 5.7, see Section 1.5, “Server and Status Variables and Options Added, Deprecated, or Removed in MySQL 5.7”.

Note

Not all storage engines are supported by all MySQL server binaries and configurations. To find out how to determine which storage engines your MySQL server installation supports, see Section 14.7.5.16, “SHOW ENGINES Syntax”.

6.1.1 Configuring the Server

The MySQL server, mysqld, has many command options and system variables that can be set at startup to configure its operation. To determine the command option and system variable values used by the server, execute this command:

shell> mysqld --verbose --help

The command produces a list of all mysqld options and configurable system variables. Its output includes the default option and variable values and looks something like this:

abort-slave-event-count           0
allow-suspicious-udfs             FALSE
archive                           ON
auto-increment-increment          1
auto-increment-offset             1
autocommit                        TRUE
automatic-sp-privileges           TRUE
avoid-temporal-upgrade            FALSE
back-log                          80
basedir                           /home/jon/bin/mysql-5.7/
...
tmpdir                            /tmp
transaction-alloc-block-size      8192
transaction-isolation             REPEATABLE-READ
transaction-prealloc-size         4096
transaction-read-only             FALSE
transaction-write-set-extraction  OFF
updatable-views-with-limit        YES
validate-user-plugins             TRUE
verbose                           TRUE
wait-timeout                      28800

To see the current system variable values used by the server as it runs, connect to it and execute this statement:

mysql> SHOW VARIABLES;

To see some statistical and status indicators for a running server, execute this statement:

mysql> SHOW STATUS;

System variable and status information also is available using the mysqladmin command:

shell> mysqladmin variables
shell> mysqladmin extended-status

For a full description of all command options, system variables, and status variables, see these sections:

More detailed monitoring information is available from the Performance Schema; see Chapter 25, MySQL Performance Schema.

MySQL uses algorithms that are very scalable, so you can usually run with very little memory. However, normally better performance results from giving MySQL more memory.

When tuning a MySQL server, the two most important variables to configure are key_buffer_size and table_open_cache. You should first feel confident that you have these set appropriately before trying to change any other variables.

The following examples indicate some typical variable values for different runtime configurations.

  • If you have at least 1-2GB of memory and many tables and want maximum performance with a moderate number of clients, use something like this:

    shell> mysqld_safe --key_buffer_size=384M --table_open_cache=4000 \
               --sort_buffer_size=4M --read_buffer_size=1M &
    
  • If you have only 256MB of memory and only a few tables, but you still do a lot of sorting, you can use something like this:

    shell> mysqld_safe --key_buffer_size=64M --sort_buffer_size=1M
    

    If there are very many simultaneous connections, swapping problems may occur unless mysqld has been configured to use very little memory for each connection. mysqld performs better if you have enough memory for all connections.

  • With little memory and lots of connections, use something like this:

    shell> mysqld_safe --key_buffer_size=512K --sort_buffer_size=100K \
               --read_buffer_size=100K &
    

    Or even this:

    shell> mysqld_safe --key_buffer_size=512K --sort_buffer_size=16K \
               --table_open_cache=32 --read_buffer_size=8K \
               --net_buffer_length=1K &
    

If you are performing GROUP BY or ORDER BY operations on tables that are much larger than your available memory, increase the value of read_rnd_buffer_size to speed up the reading of rows following sorting operations.

If you specify an option on the command line for mysqld or mysqld_safe, it remains in effect only for that invocation of the server. To use the option every time the server runs, put it in an option file. See Section 5.2.6, “Using Option Files”.

6.1.2 Server Configuration Defaults

The MySQL server has many operating parameters, which you can change at server startup using command-line options or configuration files (option files). It is also possible to change many parameters at runtime. For general instructions on setting parameters at startup or runtime, see Section 6.1.4, “Server Command Options”, and Section 6.1.5, “Server System Variables”.

Before MySQL 5.7.5, on Unix platforms, mysql_install_db creates a default option file named my.cnf in the base installation directory. This file is created from a template included in the distribution package named my-default.cnf. You can find the template in or under the base installation directory. When started using mysqld_safe, the server uses my.cnf file by default. If my.cnf already exists, mysql_install_db assumes it to be in use and writes a new file named my-new.cnf instead.

Note

As of MySQL 5.7.18, my-default.cnf is no longer included in or installed by distribution packages.

With one exception, the settings in the default option file are commented and have no effect. The exception is that the file sets the sql_mode system variable to NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES. This setting produces a server configuration that results in errors rather than warnings for bad data in operations that modify transactional tables. See Section 6.1.8, “Server SQL Modes”.

On Windows, MySQL Installer interacts with the user and creates a file named my.ini in the base installation directory as the default option file. If you install on Windows from a Zip archive, you can copy the my-default.ini template file in the base installation directory to my.ini and use the latter as the default option file.

Note

As of MySQL 5.7.18, my-default.ini is no longer included in or installed by distribution packages.

Note

On Windows, the .ini or .cnf option file extension might not be displayed.

On any platform, after completing the installation process, you can edit the default option file at any time to modify the parameters used by the server. For example, to use a parameter setting in the file that is commented with a # character at the beginning of the line, remove the #, and modify the parameter value if necessary. To disable a setting, either add a # to the beginning of the line or remove it.

For additional information about option file format and syntax, see Section 5.2.6, “Using Option Files”.

6.1.3 Server Option and Variable Reference

The following table provides a list of all the command line options, server and status variables applicable within mysqld.

The table lists command-line options (Cmd-line), options valid in configuration files (Option file), server system variables (System Var), and status variables (Status var) in one unified list, with notification of where each option/variable is valid. If a server option set on the command line or in an option file differs from the name of the corresponding server system or status variable, the variable name is noted immediately below the corresponding option. For status variables, the scope of the variable is shown (Scope) as either global, session, or both. Please see the corresponding sections for details on setting and using the options and variables. Where appropriate, a direct link to further information on the item as available.

For a version of this table that is specific to MySQL Cluster, see Section 21.3.2.5, “NDB Cluster mysqld Option and Variable Reference”.

Table 6.1 Option/Variable Summary

NameCmd-LineOption FileSystem VarStatus VarVar ScopeDynamic
abort-slave-event-countYesYes    
Aborted_clients   YesGlobalNo
Aborted_connects   YesGlobalNo
allow-suspicious-udfsYesYes    
ansiYesYes    
audit-logYesYes    
audit_log_buffer_sizeYesYesYes GlobalNo
audit_log_connection_policyYesYesYes GlobalYes
audit_log_current_session  Yes BothNo
Audit_log_current_size   YesGlobalNo
Audit_log_event_max_drop_size   YesGlobalNo
Audit_log_events   YesGlobalNo
Audit_log_events_filtered   YesGlobalNo
Audit_log_events_lost   YesGlobalNo
Audit_log_events_written   YesGlobalNo
audit_log_exclude_accountsYesYesYes GlobalYes
audit_log_fileYesYesYes GlobalNo
audit_log_filter_id  Yes BothNo
audit_log_flush  Yes GlobalYes
audit_log_formatYesYesYes GlobalNo
audit_log_include_accountsYesYesYes GlobalYes
audit_log_policyYesYesYes GlobalNo
audit_log_rotate_on_sizeYesYesYes GlobalYes
audit_log_statement_policyYesYesYes GlobalYes
audit_log_strategyYesYesYes GlobalNo
Audit_log_total_size   YesGlobalNo
Audit_log_write_waits   YesGlobalNo
authentication_windows_log_levelYesYes    
authentication_windows_use_principal_nameYesYes    
auto_generate_certsYesYesYes GlobalNo
auto_increment_increment  Yes BothYes
auto_increment_offset  Yes BothYes
autocommitYesYesYes BothYes
automatic_sp_privileges  Yes GlobalYes
avoid_temporal_upgradeYesYesYes GlobalYes
back_log  Yes GlobalNo
basedirYesYesYes GlobalNo
big-tablesYesYes  BothYes
- Variable: big_tables  Yes BothYes
bind-addressYesYes  GlobalNo
- Variable: bind_address  Yes GlobalNo
Binlog_cache_disk_use   YesGlobalNo
binlog_cache_sizeYesYesYes GlobalYes
Binlog_cache_use   YesGlobalNo
binlog-checksumYesYes    
binlog_checksum  Yes GlobalYes
binlog_direct_non_transactional_updatesYesYesYes BothYes
binlog-do-dbYesYes    
binlog_error_actionYesYesYes BothYes
binlog-formatYesYes  BothYes
- Variable: binlog_format  Yes BothYes
binlog_group_commit_sync_delayYesYesYes GlobalYes
binlog_group_commit_sync_no_delay_countYesYesYes GlobalYes
binlog_gtid_simple_recoveryYesYesYes GlobalNo
binlog-ignore-dbYesYes    
binlog_max_flush_queue_time  Yes GlobalYes
binlog_order_commits  Yes GlobalYes
binlog-row-event-max-sizeYesYes    
binlog_row_imageYesYesYes BothYes
binlog-rows-query-log-eventsYesYes    
- Variable: binlog_rows_query_log_events      
binlog_rows_query_log_events  Yes BothYes
Binlog_stmt_cache_disk_use   YesGlobalNo
binlog_stmt_cache_sizeYesYesYes GlobalYes
Binlog_stmt_cache_use   YesGlobalNo
binlogging_impossible_modeYesYesYes BothYes
block_encryption_modeYesYesYes BothYes
bootstrapYesYes    
bulk_insert_buffer_sizeYesYesYes BothYes
Bytes_received   YesBothNo
Bytes_sent   YesBothNo
character_set_client  Yes BothYes
character-set-client-handshakeYesYes    
character_set_connection  Yes BothYes
character_set_database[a]  Yes BothYes
character-set-filesystemYesYes  BothYes
- Variable: character_set_filesystem  Yes BothYes
character_set_results  Yes BothYes
character-set-serverYesYes  BothYes
- Variable: character_set_server  Yes BothYes
character_set_system  Yes GlobalNo
character-sets-dirYesYes  GlobalNo
- Variable: character_sets_dir  Yes GlobalNo
check_proxy_usersYesYesYes GlobalYes
chrootYesYes    
collation_connection  Yes BothYes
collation_database[b]  Yes BothYes
collation-serverYesYes  BothYes
- Variable: collation_server  Yes BothYes
Com_admin_commands   YesBothNo
Com_alter_db   YesBothNo
Com_alter_db_upgrade   YesBothNo
Com_alter_event   YesBothNo
Com_alter_function   YesBothNo
Com_alter_procedure   YesBothNo
Com_alter_server   YesBothNo
Com_alter_table   YesBothNo
Com_alter_tablespace   YesBothNo
Com_alter_user   YesBothNo
Com_analyze   YesBothNo
Com_assign_to_keycache   YesBothNo
Com_begin   YesBothNo
Com_binlog   YesBothNo
Com_call_procedure   YesBothNo
Com_change_db   YesBothNo
Com_change_master   YesBothNo
Com_change_repl_filter   YesBothNo
Com_check   YesBothNo
Com_checksum   YesBothNo
Com_commit   YesBothNo
Com_create_db   YesBothNo
Com_create_event   YesBothNo
Com_create_function   YesBothNo
Com_create_index   YesBothNo
Com_create_procedure   YesBothNo
Com_create_server   YesBothNo
Com_create_table   YesBothNo
Com_create_trigger   YesBothNo
Com_create_udf   YesBothNo
Com_create_user   YesBothNo
Com_create_view   YesBothNo
Com_dealloc_sql   YesBothNo
Com_delete   YesBothNo
Com_delete_multi   YesBothNo
Com_do   YesBothNo
Com_drop_db   YesBothNo
Com_drop_event   YesBothNo
Com_drop_function   YesBothNo
Com_drop_index   YesBothNo
Com_drop_procedure   YesBothNo
Com_drop_server   YesBothNo
Com_drop_table   YesBothNo
Com_drop_trigger   YesBothNo
Com_drop_user   YesBothNo
Com_drop_view   YesBothNo
Com_empty_query   YesBothNo
Com_execute_sql   YesBothNo
Com_explain_other   YesBothNo
Com_flush   YesBothNo
Com_get_diagnostics   YesBothNo
Com_grant   YesBothNo
Com_group_replication_start   YesGlobalNo
Com_group_replication_stop   YesGlobalNo
Com_ha_close   YesBothNo
Com_ha_open   YesBothNo
Com_ha_read   YesBothNo
Com_help   YesBothNo
Com_insert   YesBothNo
Com_insert_select   YesBothNo
Com_install_plugin   YesBothNo
Com_kill   YesBothNo
Com_load   YesBothNo
Com_lock_tables   YesBothNo
Com_optimize   YesBothNo
Com_preload_keys   YesBothNo
Com_prepare_sql   YesBothNo
Com_purge   YesBothNo
Com_purge_before_date   YesBothNo
Com_release_savepoint   YesBothNo
Com_rename_table   YesBothNo
Com_rename_user   YesBothNo
Com_repair   YesBothNo
Com_replace   YesBothNo
Com_replace_select   YesBothNo
Com_reset   YesBothNo
Com_resignal   YesBothNo
Com_revoke   YesBothNo
Com_revoke_all   YesBothNo
Com_rollback   YesBothNo
Com_rollback_to_savepoint   YesBothNo
Com_savepoint   YesBothNo
Com_select   YesBothNo
Com_set_option   YesBothNo
Com_show_authors   YesBothNo
Com_show_binlog_events   YesBothNo
Com_show_binlogs   YesBothNo
Com_show_charsets   YesBothNo
Com_show_collations   YesBothNo
Com_show_contributors   YesBothNo
Com_show_create_db   YesBothNo
Com_show_create_event   YesBothNo
Com_show_create_func   YesBothNo
Com_show_create_proc   YesBothNo
Com_show_create_table   YesBothNo
Com_show_create_trigger   YesBothNo
Com_show_create_user   YesBothNo
Com_show_databases   YesBothNo
Com_show_engine_logs   YesBothNo
Com_show_engine_mutex   YesBothNo
Com_show_engine_status   YesBothNo
Com_show_errors   YesBothNo
Com_show_events   YesBothNo
Com_show_fields   YesBothNo
Com_show_function_code   YesBothNo
Com_show_function_status   YesBothNo
Com_show_grants   YesBothNo
Com_show_keys   YesBothNo
Com_show_master_status   YesBothNo
Com_show_ndb_status   YesBothNo
Com_show_new_master   YesBothNo
Com_show_open_tables   YesBothNo
Com_show_plugins   YesBothNo
Com_show_privileges   YesBothNo
Com_show_procedure_code   YesBothNo
Com_show_procedure_status   YesBothNo
Com_show_processlist   YesBothNo
Com_show_profile   YesBothNo
Com_show_profiles   YesBothNo
Com_show_relaylog_events   YesBothNo
Com_show_slave_hosts   YesBothNo
Com_show_slave_status   YesBothNo
Com_show_slave_status_nonblocking   YesBothNo
Com_show_status   YesBothNo
Com_show_storage_engines   YesBothNo
Com_show_table_status   YesBothNo
Com_show_tables   YesBothNo
Com_show_triggers   YesBothNo
Com_show_variables   YesBothNo
Com_show_warnings   YesBothNo
Com_shutdown   YesBothNo
Com_signal   YesBothNo
Com_slave_start   YesBothNo
Com_slave_stop   YesBothNo
Com_stmt_close   YesBothNo
Com_stmt_execute   YesBothNo
Com_stmt_fetch   YesBothNo
Com_stmt_prepare   YesBothNo
Com_stmt_reprepare   YesBothNo
Com_stmt_reset   YesBothNo
Com_stmt_send_long_data   YesBothNo
Com_truncate   YesBothNo
Com_uninstall_plugin   YesBothNo
Com_unlock_tables   YesBothNo
Com_update   YesBothNo
Com_update_multi   YesBothNo
Com_xa_commit   YesBothNo
Com_xa_end   YesBothNo
Com_xa_prepare   YesBothNo
Com_xa_recover   YesBothNo
Com_xa_rollback   YesBothNo
Com_xa_start   YesBothNo
completion_typeYesYesYes BothYes
Compression   YesSessionNo
concurrent_insertYesYesYes GlobalYes
connect_timeoutYesYesYes GlobalYes
Connection_control_delay_generated   YesGlobalNo
connection_control_failed_connections_thresholdYesYesYes GlobalYes
connection_control_max_connection_delayYesYesYes GlobalYes
connection_control_min_connection_delayYesYesYes GlobalYes
Connection_errors_accept   YesGlobalNo
Connection_errors_internal   YesGlobalNo
Connection_errors_max_connections   YesGlobalNo
Connection_errors_peer_addr   YesGlobalNo
Connection_errors_select   YesGlobalNo
Connection_errors_tcpwrap   YesGlobalNo
Connections   YesGlobalNo
consoleYesYes    
core-fileYesYes    
core_file  Yes GlobalNo
Created_tmp_disk_tables   YesBothNo
Created_tmp_files   YesGlobalNo
Created_tmp_tables   YesBothNo
daemon_memcached_enable_binlogYesYesYes GlobalNo
daemon_memcached_engine_lib_nameYesYesYes GlobalNo
daemon_memcached_engine_lib_pathYesYesYes GlobalNo
daemon_memcached_optionYesYesYes GlobalNo
daemon_memcached_r_batch_sizeYesYesYes GlobalNo
daemon_memcached_w_batch_sizeYesYesYes GlobalNo
daemonizeYesYes    
datadirYesYesYes GlobalNo
date_format  Yes GlobalNo
datetime_format  Yes GlobalNo
debugYesYesYes BothYes
debug_sync  Yes SessionYes
debug-sync-timeoutYesYes    
default-authentication-pluginYesYes    
default_authentication_pluginYesYesYes GlobalNo
default_password_lifetimeYesYesYes GlobalYes
default-storage-engineYesYes  BothYes
- Variable: default_storage_engine  Yes BothYes
default-time-zoneYesYes    
default_tmp_storage_engineYesYesYes BothYes
default_week_formatYesYesYes BothYes
defaults-extra-fileYes     
defaults-fileYes     
defaults-group-suffixYes     
delay-key-writeYesYes  GlobalYes
- Variable: delay_key_write  Yes GlobalYes
Delayed_errors   YesGlobalNo
delayed_insert_limitYesYesYes GlobalYes
Delayed_insert_threads   YesGlobalNo
delayed_insert_timeoutYesYesYes GlobalYes
delayed_queue_sizeYesYesYes GlobalYes
Delayed_writes   YesGlobalNo
des-key-fileYesYes    
disable-partition-engine-checkYesYes    
disabled_storage_enginesYesYesYes GlobalNo
disconnect_on_expired_passwordYesYesYes SessionNo
disconnect-slave-event-countYesYes    
div_precision_incrementYesYesYes BothYes
early-plugin-loadYesYes    
enable-named-pipeYesYes    
- Variable: named_pipe      
end_markers_in_json  Yes BothYes
enforce-gtid-consistencyYesYesYes GlobalVaries
enforce_gtid_consistencyYesYesYes GlobalVaries
eq_range_index_dive_limit  Yes BothYes
error_count  Yes SessionNo
event-schedulerYesYes  GlobalYes
- Variable: event_scheduler  Yes GlobalYes
executed-gtids-compression-periodYesYes    
- Variable: executed_gtids_compression_period      
executed_gtids_compression_period  Yes GlobalYes
exit-infoYesYes    
expire_logs_daysYesYesYes GlobalYes
explicit_defaults_for_timestampYesYesYes BothYes
external-lockingYesYes    
- Variable: skip_external_locking      
external_user  Yes SessionNo
federatedYesYes    
Firewall_access_denied   YesGlobalNo
Firewall_access_granted   YesGlobalNo
Firewall_cached_entries   YesGlobalNo
flushYesYesYes GlobalYes
Flush_commands   YesGlobalNo
flush_timeYesYesYes GlobalYes
foreign_key_checks  Yes BothYes
ft_boolean_syntaxYesYesYes GlobalYes
ft_max_word_lenYesYesYes GlobalNo
ft_min_word_lenYesYesYes GlobalNo
ft_query_expansion_limitYesYesYes GlobalNo
ft_stopword_fileYesYesYes GlobalNo
gdbYesYes    
general-logYesYes  GlobalYes
- Variable: general_log  Yes GlobalYes
general_log_fileYesYesYes GlobalYes
group_concat_max_lenYesYesYes BothYes
group_replication_allow_local_disjoint_gtids_joinYesYesYes GlobalYes
group_replication_allow_local_lower_version_joinYesYesYes GlobalYes
group_replication_auto_increment_incrementYesYesYes GlobalYes
group_replication_bootstrap_groupYesYesYes GlobalYes
group_replication_components_stop_timeoutYesYesYes GlobalYes
group_replication_compression_thresholdYesYesYes GlobalYes
group_replication_enforce_update_everywhere_checksYesYesYes GlobalYes
group_replication_flow_control_applier_thresholdYesYesYes GlobalYes
group_replication_flow_control_certifier_thresholdYesYesYes GlobalYes
group_replication_flow_control_modeYesYesYes GlobalYes
group_replication_force_membersYesYesYes GlobalYes
group_replication_group_nameYesYesYes GlobalYes
group_replication_group_seedsYesYesYes GlobalYes
group_replication_gtid_assignment_block_sizeYesYesYes GlobalYes
group_replication_ip_whitelistYesYesYes GlobalYes
group_replication_local_addressYesYesYes GlobalYes
group_replication_poll_spin_loopsYesYesYes GlobalYes
group_replication_recovery_complete_atYesYesYes GlobalYes
group_replication_recovery_reconnect_intervalYesYesYes GlobalYes
group_replication_recovery_retry_countYesYesYes GlobalYes
group_replication_recovery_ssl_caYesYesYes GlobalYes
group_replication_recovery_ssl_capathYesYesYes GlobalYes
group_replication_recovery_ssl_certYesYesYes GlobalYes
group_replication_recovery_ssl_cipherYesYesYes GlobalYes
group_replication_recovery_ssl_crlYesYesYes GlobalYes
group_replication_recovery_ssl_crlpathYesYesYes GlobalYes
group_replication_recovery_ssl_keyYesYesYes GlobalYes
group_replication_recovery_ssl_verify_server_certYesYesYes GlobalYes
group_replication_recovery_use_sslYesYesYes GlobalYes
group_replication_single_primary_modeYesYesYes GlobalYes
group_replication_ssl_modeYesYesYes GlobalYes
group_replication_start_on_bootYesYesYes GlobalYes
gtid_executed  Yes VariesNo
gtid-executed-compression-periodYesYes    
- Variable: gtid_executed_compression_period      
gtid_executed_compression_period  Yes GlobalYes
gtid-modeYesYes  GlobalVaries
- Variable: gtid_mode  Yes GlobalVaries
gtid_mode  Yes GlobalVaries
gtid_next  Yes SessionYes
gtid_owned  Yes BothNo
gtid_purged  Yes GlobalYes
Handler_commit   YesBothNo
Handler_delete   YesBothNo
Handler_discover   YesBothNo
Handler_external_lock   YesBothNo
Handler_mrr_init   YesBothNo
Handler_prepare   YesBothNo
Handler_read_first   YesBothNo
Handler_read_key   YesBothNo
Handler_read_last   YesBothNo
Handler_read_next   YesBothNo
Handler_read_prev   YesBothNo
Handler_read_rnd   YesBothNo
Handler_read_rnd_next   YesBothNo
Handler_rollback   YesBothNo
Handler_savepoint   YesBothNo
Handler_savepoint_rollback   YesBothNo
Handler_update   YesBothNo
Handler_write   YesBothNo
have_compress  Yes GlobalNo
have_crypt  Yes GlobalNo
have_dynamic_loading  Yes GlobalNo
have_geometry  Yes GlobalNo
have_openssl  Yes GlobalNo
have_profiling  Yes GlobalNo
have_query_cache  Yes GlobalNo
have_rtree_keys  Yes GlobalNo
have_ssl  Yes GlobalNo
have_statement_timeout  Yes GlobalNo
have_symlink  Yes GlobalNo
helpYesYes    
host_cache_size  Yes GlobalYes
hostname  Yes GlobalNo
identity  Yes SessionYes
ignore-builtin-innodbYesYes  GlobalNo
- Variable: ignore_builtin_innodb  Yes GlobalNo
ignore-db-dirYesYes    
ignore_db_dirs  Yes GlobalNo
init_connectYesYesYes GlobalYes
init-fileYesYes  GlobalNo
- Variable: init_file  Yes GlobalNo
init_slaveYesYesYes GlobalYes
initializeYesYes    
initialize-insecureYesYes    
innodbYesYes    
innodb_adaptive_flushingYesYesYes GlobalYes
innodb_adaptive_flushing_lwmYesYesYes GlobalYes
innodb_adaptive_hash_indexYesYesYes GlobalYes
innodb_adaptive_hash_index_partsYesYesYes GlobalNo
innodb_adaptive_max_sleep_delayYesYesYes GlobalYes
innodb_additional_mem_pool_sizeYesYesYes GlobalNo
innodb_api_bk_commit_intervalYesYesYes GlobalYes
innodb_api_disable_rowlockYesYesYes GlobalNo
innodb_api_enable_binlogYesYesYes GlobalNo
innodb_api_enable_mdlYesYesYes GlobalNo
innodb_api_trx_levelYesYesYes GlobalYes
innodb_autoextend_incrementYesYesYes GlobalYes
innodb_autoinc_lock_modeYesYesYes GlobalNo
Innodb_available_undo_logs   YesGlobalNo
innodb_background_drop_list_emptyYesYesYes GlobalYes
Innodb_buffer_pool_bytes_data   YesGlobalNo
Innodb_buffer_pool_bytes_dirty   YesGlobalNo
innodb_buffer_pool_chunk_sizeYesYesYes GlobalNo
innodb_buffer_pool_dump_at_shutdownYesYesYes GlobalYes
innodb_buffer_pool_dump_nowYesYesYes GlobalYes
innodb_buffer_pool_dump_pctYesYesYes GlobalYes
Innodb_buffer_pool_dump_status   YesGlobalNo
innodb_buffer_pool_filenameYesYesYes GlobalYes
innodb_buffer_pool_instancesYesYesYes GlobalNo
innodb_buffer_pool_load_abortYesYesYes GlobalYes
innodb_buffer_pool_load_at_startupYesYesYes GlobalNo
innodb_buffer_pool_load_nowYesYesYes GlobalYes
Innodb_buffer_pool_load_status   YesGlobalNo
Innodb_buffer_pool_pages_data   YesGlobalNo
Innodb_buffer_pool_pages_dirty   YesGlobalNo
Innodb_buffer_pool_pages_flushed   YesGlobalNo
Innodb_buffer_pool_pages_free   YesGlobalNo
Innodb_buffer_pool_pages_latched   YesGlobalNo
Innodb_buffer_pool_pages_misc   YesGlobalNo
Innodb_buffer_pool_pages_total   YesGlobalNo
Innodb_buffer_pool_read_ahead   YesGlobalNo
Innodb_buffer_pool_read_ahead_evicted   YesGlobalNo
Innodb_buffer_pool_read_ahead_rnd   YesGlobalNo
Innodb_buffer_pool_read_requests   YesGlobalNo
Innodb_buffer_pool_reads   YesGlobalNo
Innodb_buffer_pool_resize_status   YesGlobalNo
innodb_buffer_pool_sizeYesYesYes GlobalVaries
Innodb_buffer_pool_wait_free   YesGlobalNo
Innodb_buffer_pool_write_requests   YesGlobalNo
innodb_change_buffer_max_sizeYesYesYes GlobalYes
innodb_change_bufferingYesYesYes GlobalYes
innodb_change_buffering_debugYesYesYes GlobalYes
innodb_checksum_algorithmYesYesYes GlobalYes
innodb_checksumsYesYesYes GlobalNo
innodb_cmp_per_index_enabledYesYesYes GlobalYes
innodb_commit_concurrencyYesYesYes GlobalYes
innodb_compress_debugYesYesYes GlobalYes
innodb_compression_failure_threshold_pctYesYesYes GlobalYes
innodb_compression_levelYesYesYes GlobalYes
innodb_compression_pad_pct_maxYesYesYes GlobalYes
innodb_concurrency_ticketsYesYesYes GlobalYes
innodb_create_intrinsicYesYesYes SessionYes
innodb_data_file_pathYesYesYes GlobalNo
Innodb_data_fsyncs   YesGlobalNo
innodb_data_home_dirYesYesYes GlobalNo
Innodb_data_pending_fsyncs   YesGlobalNo
Innodb_data_pending_reads   YesGlobalNo
Innodb_data_pending_writes   YesGlobalNo
Innodb_data_read   YesGlobalNo
Innodb_data_reads   YesGlobalNo
Innodb_data_writes   YesGlobalNo
Innodb_data_written   YesGlobalNo
Innodb_dblwr_pages_written   YesGlobalNo
Innodb_dblwr_writes   YesGlobalNo
innodb_deadlock_detectYesYesYes GlobalYes
innodb_default_row_formatYesYesYes GlobalYes
innodb_disable_resize_buffer_pool_debugYesYesYes GlobalYes
innodb_disable_sort_file_cacheYesYesYes GlobalYes
innodb_doublewriteYesYesYes GlobalNo
innodb_fast_shutdownYesYesYes GlobalYes
innodb_fil_make_page_dirty_debugYesYesYes GlobalYes
innodb_file_formatYesYesYes GlobalYes
innodb_file_format_checkYesYesYes GlobalNo
innodb_file_format_maxYesYesYes GlobalYes
innodb_file_per_tableYesYesYes GlobalYes
innodb_fill_factorYesYesYes GlobalYes
innodb_flush_log_at_timeout  Yes GlobalYes
innodb_flush_log_at_trx_commitYesYesYes GlobalYes
innodb_flush_methodYesYesYes GlobalNo
innodb_flush_neighborsYesYesYes GlobalYes
innodb_flush_syncYesYesYes GlobalYes
innodb_flushing_avg_loopsYesYesYes GlobalYes
innodb_force_load_corruptedYesYesYes GlobalNo
innodb_force_recoveryYesYesYes GlobalNo
innodb_ft_aux_tableYesYesYes GlobalYes
innodb_ft_cache_sizeYesYesYes GlobalNo
innodb_ft_enable_diag_printYesYesYes GlobalYes
innodb_ft_enable_stopwordYesYesYes GlobalYes
innodb_ft_max_token_sizeYesYesYes GlobalNo
innodb_ft_min_token_sizeYesYesYes GlobalNo
innodb_ft_num_word_optimizeYesYesYes GlobalYes
innodb_ft_result_cache_limitYesYesYes GlobalYes
innodb_ft_server_stopword_tableYesYesYes GlobalYes
innodb_ft_sort_pll_degreeYesYesYes GlobalNo
innodb_ft_total_cache_sizeYesYesYes GlobalNo
innodb_ft_user_stopword_tableYesYesYes BothYes
Innodb_have_atomic_builtins   YesGlobalNo
innodb_io_capacityYesYesYes GlobalYes
innodb_io_capacity_maxYesYesYes GlobalYes
innodb_large_prefixYesYesYes GlobalYes
innodb_limit_optimistic_insert_debugYesYesYes GlobalYes
innodb_lock_wait_timeoutYesYesYes BothYes
innodb_locks_unsafe_for_binlogYesYesYes GlobalNo
innodb_log_buffer_sizeYesYesYes GlobalNo
innodb_log_checksum_algorithmYesYesYes GlobalYes
innodb_log_checksumsYesYesYes GlobalYes
innodb_log_compressed_pagesYesYesYes GlobalYes
innodb_log_file_sizeYesYesYes GlobalNo
innodb_log_files_in_groupYesYesYes GlobalNo
innodb_log_group_home_dirYesYesYes GlobalNo
Innodb_log_waits   YesGlobalNo
innodb_log_write_ahead_sizeYesYesYes GlobalYes
Innodb_log_write_requests   YesGlobalNo
Innodb_log_writes   YesGlobalNo
innodb_lru_scan_depthYesYesYes GlobalYes
innodb_max_dirty_pages_pctYesYesYes GlobalYes
innodb_max_dirty_pages_pct_lwmYesYesYes GlobalYes
innodb_max_purge_lagYesYesYes GlobalYes
innodb_max_purge_lag_delayYesYesYes GlobalYes
innodb_max_undo_log_sizeYesYesYes GlobalYes
innodb_merge_threshold_set_all_debugYesYesYes GlobalYes
innodb_monitor_disableYesYesYes GlobalYes
innodb_monitor_enableYesYesYes GlobalYes
innodb_monitor_resetYesYesYes GlobalYes
innodb_monitor_reset_allYesYesYes GlobalYes
Innodb_num_open_files   YesGlobalNo
innodb_numa_interleaveYesYesYes GlobalNo
innodb_old_blocks_pctYesYesYes GlobalYes
innodb_old_blocks_timeYesYesYes GlobalYes
innodb_online_alter_log_max_sizeYesYesYes GlobalYes
innodb_open_filesYesYesYes GlobalNo
innodb_optimize_fulltext_onlyYesYesYes GlobalYes
innodb_optimize_point_storageYesYesYes SessionYes
Innodb_os_log_fsyncs   YesGlobalNo
Innodb_os_log_pending_fsyncs   YesGlobalNo
Innodb_os_log_pending_writes   YesGlobalNo
Innodb_os_log_written   YesGlobalNo
innodb_page_cleanersYesYesYes GlobalNo
Innodb_page_size   YesGlobalNo
innodb_page_sizeYesYesYes GlobalNo
Innodb_pages_created   YesGlobalNo
Innodb_pages_read   YesGlobalNo
Innodb_pages_written   YesGlobalNo
innodb_print_all_deadlocksYesYesYes GlobalYes
innodb_purge_batch_sizeYesYesYes GlobalYes
innodb_purge_rseg_truncate_frequencyYesYesYes GlobalYes
innodb_purge_threadsYesYesYes GlobalNo
innodb_random_read_aheadYesYesYes GlobalYes
innodb_read_ahead_thresholdYesYesYes GlobalYes
innodb_read_io_threadsYesYesYes GlobalNo
innodb_read_onlyYesYesYes GlobalNo
innodb_replication_delayYesYesYes GlobalYes
innodb_rollback_on_timeoutYesYesYes GlobalNo
innodb_rollback_segmentsYesYesYes GlobalYes
Innodb_row_lock_current_waits   YesGlobalNo
Innodb_row_lock_time   YesGlobalNo
Innodb_row_lock_time_avg   YesGlobalNo
Innodb_row_lock_time_max   YesGlobalNo
Innodb_row_lock_waits   YesGlobalNo
Innodb_rows_deleted   YesGlobalNo
Innodb_rows_inserted   YesGlobalNo
Innodb_rows_read   YesGlobalNo
Innodb_rows_updated   YesGlobalNo
innodb_saved_page_number_debugYesYesYes GlobalYes
innodb_sort_buffer_sizeYesYesYes GlobalNo
innodb_spin_wait_delayYesYesYes GlobalYes
innodb_stats_auto_recalcYesYesYes GlobalYes
innodb_stats_include_delete_markedYesYesYes GlobalYes
innodb_stats_methodYesYesYes GlobalYes
innodb_stats_on_metadataYesYesYes GlobalYes
innodb_stats_persistentYesYesYes GlobalYes
innodb_stats_persistent_sample_pagesYesYesYes GlobalYes
innodb_stats_sample_pagesYesYesYes GlobalYes
innodb_stats_transient_sample_pagesYesYesYes GlobalYes
innodb-status-fileYesYes    
innodb_status_outputYesYesYes GlobalYes
innodb_status_output_locksYesYesYes GlobalYes
innodb_strict_modeYesYesYes BothYes
innodb_support_xaYesYesYes BothYes
innodb_sync_array_sizeYesYesYes GlobalNo
innodb_sync_debugYesYesYes GlobalNo
innodb_sync_spin_loopsYesYesYes GlobalYes
innodb_table_locksYesYesYes BothYes
innodb_temp_data_file_pathYesYesYes GlobalNo
innodb_thread_concurrencyYesYesYes GlobalYes
innodb_thread_sleep_delayYesYesYes GlobalYes
innodb_tmpdirYesYesYes BothYes
Innodb_truncated_status_writes   YesGlobalNo
innodb_trx_purge_view_update_only_debugYesYesYes GlobalYes
innodb_trx_rseg_n_slots_debugYesYesYes GlobalYes
innodb_undo_directoryYesYesYes GlobalNo
innodb_undo_log_truncateYesYesYes GlobalYes
innodb_undo_logsYesYesYes GlobalYes
innodb_undo_tablespacesYesYesYes GlobalNo
innodb_use_native_aioYesYesYes GlobalNo
innodb_use_sys_mallocYesYesYes GlobalNo
innodb_version  Yes GlobalNo
innodb_write_io_threadsYesYesYes GlobalNo
insert_id  Yes SessionYes
installYes     
install-manualYes     
interactive_timeoutYesYesYes BothYes
internal_tmp_disk_storage_engineYesYesYes GlobalYes
join_buffer_sizeYesYesYes BothYes
keep_files_on_createYesYesYes BothYes
Key_blocks_not_flushed   YesGlobalNo
Key_blocks_unused   YesGlobalNo
Key_blocks_used   YesGlobalNo
key_buffer_sizeYesYesYes GlobalYes
key_cache_age_thresholdYesYesYes GlobalYes
key_cache_block_sizeYesYesYes GlobalYes
key_cache_division_limitYesYesYes GlobalYes
Key_read_requests   YesGlobalNo
Key_reads   YesGlobalNo
Key_write_requests   YesGlobalNo
Key_writes   YesGlobalNo
keyring_file_dataYesYesYes GlobalYes
keyring_okv_conf_dirYesYesYes GlobalYes
languageYesYesYes GlobalNo
large_files_support  Yes GlobalNo
large_page_size  Yes GlobalNo
large-pagesYesYes  GlobalNo
- Variable: large_pages  Yes GlobalNo
last_insert_id  Yes SessionYes
Last_query_cost   YesSessionNo
Last_query_partial_plans   YesSessionNo
lc-messagesYesYes  BothYes
- Variable: lc_messages  Yes BothYes
lc-messages-dirYesYes  GlobalNo
- Variable: lc_messages_dir  Yes GlobalNo
lc_time_names  Yes BothYes
license  Yes GlobalNo
local_infile  Yes GlobalYes
local-serviceYes     
lock_wait_timeoutYesYesYes BothYes
Locked_connects   YesGlobalNo
locked_in_memory  Yes GlobalNo
log_backward_compatible_user_definitionsYesYesYes GlobalYes
log-binYesYesYes GlobalNo
log_bin  Yes GlobalNo
log_bin_basename  Yes GlobalNo
log-bin-indexYesYes    
log_bin_index  Yes GlobalNo
log-bin-trust-function-creatorsYesYes  GlobalYes
- Variable: log_bin_trust_function_creators  Yes GlobalYes
log-bin-use-v1-row-eventsYesYes  GlobalNo
- Variable: log_bin_use_v1_row_events  Yes GlobalNo
log_bin_use_v1_row_eventsYesYesYes GlobalNo
log_builtin_as_identified_by_passwordYesYesYes GlobalYes
log-errorYesYes  GlobalNo
- Variable: log_error  Yes GlobalNo
log_error_verbosityYesYesYes GlobalYes
log-isamYesYes    
log-outputYesYes  GlobalYes
- Variable: log_output  Yes GlobalYes
log-queries-not-using-indexesYesYes  GlobalYes
- Variable: log_queries_not_using_indexes  Yes GlobalYes
log-rawYesYes    
log-short-formatYesYes    
log-slave-updatesYesYes  GlobalNo
- Variable: log_slave_updates  Yes GlobalNo
log_slave_updatesYesYesYes GlobalNo
log-slow-admin-statementsYesYes    
log_slow_admin_statements  Yes GlobalYes
log-slow-slave-statementsYesYes    
log_slow_slave_statements  Yes GlobalYes
log_statements_unsafe_for_binlog  Yes GlobalYes
log_syslogYesYesYes GlobalYes
log_syslog_facilityYesYesYes GlobalYes
log_syslog_include_pidYesYesYes GlobalYes
log_syslog_tagYesYesYes GlobalYes
log-tcYesYes    
log-tc-sizeYesYes    
log_throttle_queries_not_using_indexes  Yes GlobalYes
log_timestampsYesYesYes GlobalYes
log-warningsYesYes  GlobalYes
- Variable: log_warnings  Yes GlobalYes
long_query_timeYesYesYes BothYes
low-priority-updatesYesYes  BothYes
- Variable: low_priority_updates  Yes BothYes
lower_case_file_system  Yes GlobalNo
lower_case_table_namesYesYesYes GlobalNo
master-info-fileYesYes    
master-info-repositoryYesYes    
- Variable: master_info_repository      
master_info_repositoryYesYesYes GlobalYes
master-retry-countYesYes    
master-verify-checksumYesYes    
- Variable: master_verify_checksum      
master_verify_checksum  Yes GlobalYes
max_allowed_packetYesYesYes BothYes
max_binlog_cache_sizeYesYesYes GlobalYes
max-binlog-dump-eventsYesYes    
max_binlog_sizeYesYesYes GlobalYes
max_binlog_stmt_cache_sizeYesYesYes GlobalYes
max_connect_errorsYesYesYes GlobalYes
max_connectionsYesYesYes GlobalYes
max_delayed_threadsYesYesYes BothYes
max_digest_lengthYesYesYes GlobalNo
max_error_countYesYesYes BothYes
max_execution_timeYesYesYes BothYes
Max_execution_time_exceeded   YesBothNo
Max_execution_time_set   YesBothNo
Max_execution_time_set_failed   YesBothNo
max_heap_table_sizeYesYesYes BothYes
max_insert_delayed_threads  Yes BothYes
max_join_sizeYesYesYes BothYes
max_length_for_sort_dataYesYesYes BothYes
max_points_in_geometryYesYesYes GlobalYes
max_prepared_stmt_countYesYesYes GlobalYes
max_relay_log_sizeYesYesYes GlobalYes
max_seeks_for_keyYesYesYes BothYes
max_sort_lengthYesYesYes BothYes
max_sp_recursion_depthYesYesYes BothYes
max_statement_time  Yes BothYes
Max_statement_time_exceeded   YesBothNo
Max_statement_time_set   YesBothNo
Max_statement_time_set_failed   YesBothNo
max_tmp_tables  Yes BothYes
Max_used_connections   YesGlobalNo
Max_used_connections_time   YesGlobalNo
max_user_connectionsYesYesYes BothYes
max_write_lock_countYesYesYes GlobalYes
mecab_charset   YesGlobalNo
mecab_rc_fileYesYesYes GlobalNo
memlockYesYes    
- Variable: locked_in_memory      
metadata_locks_cache_size  Yes GlobalNo
metadata_locks_hash_instances  Yes GlobalNo
min-examined-row-limitYesYesYes BothYes
multi_range_countYesYesYes BothYes
myisam-block-sizeYesYes    
myisam_data_pointer_sizeYesYesYes GlobalYes
myisam_max_sort_file_sizeYesYesYes GlobalYes
myisam_mmap_sizeYesYesYes GlobalNo
myisam-recover-optionsYesYes    
- Variable: myisam_recover_options      
myisam_recover_options  Yes GlobalNo
myisam_repair_threadsYesYesYes BothYes
myisam_sort_buffer_sizeYesYesYes BothYes
myisam_stats_methodYesYesYes BothYes
myisam_use_mmapYesYesYes GlobalYes
mysql_firewall_modeYesYesYes GlobalYes
mysql_firewall_traceYesYesYes GlobalYes
mysql_native_password_proxy_usersYesYesYes GlobalYes
Mysqlx_address   YesGlobalNo
mysqlx_bind_addressYesYesYes GlobalNo
Mysqlx_bytes_received   YesBothNo
Mysqlx_bytes_sent   YesBothNo
mysqlx_connect_timeoutYesYesYes GlobalYes
Mysqlx_connection_accept_errors   YesBothNo
Mysqlx_connection_errors   YesBothNo
Mysqlx_connections_accepted   YesGlobalNo
Mysqlx_connections_closed   YesGlobalNo
Mysqlx_connections_rejected   YesGlobalNo
Mysqlx_crud_delete   YesBothNo
Mysqlx_crud_find   YesBothNo
Mysqlx_crud_insert   YesBothNo
Mysqlx_crud_update   YesBothNo
Mysqlx_errors_sent   YesBothNo
Mysqlx_expect_close   YesBothNo
Mysqlx_expect_open   YesBothNo
mysqlx_idle_worker_thread_timeoutYesYes    
Mysqlx_init_error   YesBothNo
mysqlx_max_allowed_packetYesYes    
mysqlx_max_connectionsYesYesYes GlobalYes
mysqlx_min_worker_threadsYesYes    
Mysqlx_notice_other_sent   YesBothNo
Mysqlx_notice_warning_sent   YesBothNo
Mysqlx_port   YesGlobalNo
mysqlx_portYesYesYes GlobalNo
mysqlx_port_open_timeoutYesYesYes GlobalNo
Mysqlx_rows_sent   YesBothNo
Mysqlx_sessions   YesGlobalNo
Mysqlx_sessions_accepted   YesGlobalNo
Mysqlx_sessions_closed   YesGlobalNo
Mysqlx_sessions_fatal_error   YesGlobalNo
Mysqlx_sessions_killed   YesGlobalNo
Mysqlx_sessions_rejected   YesGlobalNo
Mysqlx_socket   YesGlobalNo
mysqlx-socketYesYesYes GlobalNo
mysqlx_socket  Yes GlobalNo
mysqlx_sslYesYesYes GlobalNo
Mysqlx_ssl_accept_renegotiates   YesGlobalNo
Mysqlx_ssl_accepts   YesGlobalNo
Mysqlx_ssl_active   YesBothNo
mysqlx_ssl_caYesYesYes GlobalNo
mysqlx_ssl_capathYesYesYes GlobalNo
mysqlx_ssl_certYesYesYes GlobalNo
Mysqlx_ssl_cipher   YesBothNo
mysqlx_ssl_cipherYesYes    
Mysqlx_ssl_cipher_list   YesBothNo
mysqlx_ssl_crlYesYesYes GlobalNo
mysqlx_ssl_crlpathYesYesYes GlobalNo
Mysqlx_ssl_ctx_verify_depth   YesBothNo
Mysqlx_ssl_ctx_verify_mode   YesBothNo
Mysqlx_ssl_finished_accepts   YesGlobalNo
mysqlx_ssl_keyYesYesYes GlobalNo
Mysqlx_ssl_server_not_after   YesGlobalNo
Mysqlx_ssl_server_not_before   YesGlobalNo
Mysqlx_ssl_verify_depth   YesGlobalNo
Mysqlx_ssl_verify_mode   YesGlobalNo
Mysqlx_ssl_version   YesBothNo
Mysqlx_stmt_create_collection   YesBothNo
Mysqlx_stmt_create_collection_index   YesBothNo
Mysqlx_stmt_disable_notices   YesBothNo
Mysqlx_stmt_drop_collection   YesBothNo
Mysqlx_stmt_drop_collection_index   YesBothNo
Mysqlx_stmt_enable_notices   YesBothNo
Mysqlx_stmt_execute_sql   YesBothNo
Mysqlx_stmt_execute_xplugin   YesBothNo
Mysqlx_stmt_kill_client   YesBothNo
Mysqlx_stmt_list_clients   YesBothNo
Mysqlx_stmt_list_notices   YesBothNo
Mysqlx_stmt_list_objects   YesBothNo
Mysqlx_stmt_ping   YesBothNo
Mysqlx_worker_threads   YesGlobalNo
Mysqlx_worker_threads_active   YesGlobalNo
named_pipe  Yes GlobalNo
ndb-allow-copying-alter-tableYesYesYes BothYes
Ndb_api_bytes_received_count   YesGlobalNo
Ndb_api_bytes_received_count_session   YesSessionNo
Ndb_api_bytes_received_count_slave   YesGlobalNo
Ndb_api_bytes_sent_count   YesGlobalNo
Ndb_api_bytes_sent_count_slave   YesGlobalNo
Ndb_api_event_bytes_count_injector   YesGlobalNo
Ndb_api_event_data_count_injector   YesGlobalNo
Ndb_api_event_nondata_count_injector   YesGlobalNo
Ndb_api_pk_op_count   YesGlobalNo
Ndb_api_pk_op_count_session   YesSessionNo
Ndb_api_pk_op_count_slave   YesGlobalNo
Ndb_api_pruned_scan_count   YesGlobalNo
Ndb_api_pruned_scan_count_session   YesSessionNo
Ndb_api_range_scan_count_slave   YesGlobalNo
Ndb_api_read_row_count   YesGlobalNo
Ndb_api_read_row_count_session   YesSessionNo
Ndb_api_scan_batch_count_slave   YesGlobalNo
Ndb_api_table_scan_count   YesGlobalNo
Ndb_api_table_scan_count_session   YesSessionNo
Ndb_api_trans_abort_count   YesGlobalNo
Ndb_api_trans_abort_count_session   YesSessionNo
Ndb_api_trans_abort_count_slave   YesGlobalNo
Ndb_api_trans_close_count   YesGlobalNo
Ndb_api_trans_close_count_session   YesSessionNo
Ndb_api_trans_close_count_slave   YesGlobalNo
Ndb_api_trans_commit_count   YesGlobalNo
Ndb_api_trans_commit_count_session   YesSessionNo
Ndb_api_trans_commit_count_slave   YesGlobalNo
Ndb_api_trans_local_read_row_count_slave   YesGlobalNo
Ndb_api_trans_start_count   YesGlobalNo
Ndb_api_trans_start_count_session   YesSessionNo
Ndb_api_trans_start_count_slave   YesGlobalNo
Ndb_api_uk_op_count   YesGlobalNo
Ndb_api_uk_op_count_slave   YesGlobalNo
Ndb_api_wait_exec_complete_count   YesGlobalNo
Ndb_api_wait_exec_complete_count_session   YesSessionNo
Ndb_api_wait_exec_complete_count_slave   YesGlobalNo
Ndb_api_wait_meta_request_count   YesGlobalNo
Ndb_api_wait_meta_request_count_session   YesSessionNo
Ndb_api_wait_nanos_count   YesGlobalNo
Ndb_api_wait_nanos_count_session   YesSessionNo
Ndb_api_wait_nanos_count_slave   YesGlobalNo
Ndb_api_wait_scan_result_count   YesGlobalNo
Ndb_api_wait_scan_result_count_session   YesSessionNo
Ndb_api_wait_scan_result_count_slave   YesGlobalNo
ndb_autoincrement_prefetch_szYesYesYes BothYes
ndb-batch-sizeYesYesYes GlobalNo
ndb-blob-read-batch-bytesYesYesYes BothYes
ndb-blob-write-batch-bytesYesYesYes BothYes
ndb_cache_check_timeYesYesYes GlobalYes
ndb_clear_apply_statusYes Yes GlobalYes
ndb-cluster-connection-poolYesYesYes GlobalNo
ndb-cluster-connection-pool-nodeidsYesYesYes GlobalNo
Ndb_cluster_node_id   YesBothNo
Ndb_config_from_host   YesBothNo
Ndb_config_from_port   YesBothNo
Ndb_conflict_fn_epoch_trans   YesGlobalNo
Ndb_conflict_fn_max   YesGlobalNo
Ndb_conflict_fn_old   YesGlobalNo
Ndb_conflict_trans_detect_iter_count   YesGlobalNo
Ndb_conflict_trans_row_reject_count   YesGlobalNo
ndb-connectstringYesYes    
ndb_data_node_neighbourYesYesYes GlobalYes
ndb-default-column-formatYesYes  GlobalYes
- Variable: ndb_default_column_format  Yes GlobalYes
ndb_default_column_formatYesYesYes GlobalYes
ndb-deferred-constraintsYesYes  BothYes
- Variable: ndb_deferred_constraints  Yes BothYes
ndb_deferred_constraintsYesYesYes BothYes
ndb-distributionYesYes  GlobalYes
- Variable: ndb_distribution  Yes GlobalYes
ndb_distributionYesYesYes GlobalYes
ndb_eventbuffer_free_percentYesYesYes GlobalYes
ndb_eventbuffer_max_allocYesYesYes GlobalYes
ndb_extra_loggingYesYesYes GlobalYes
ndb_force_sendYesYesYes BothYes
ndb_fully_replicatedYesYesYes BothYes
ndb_index_stat_enableYesYesYes BothYes
ndb_index_stat_optionYesYesYes BothYes
ndb_join_pushdown  Yes BothYes
Ndb_last_commit_epoch_server   YesGlobalNo
Ndb_last_commit_epoch_session   YesSessionNo
ndb-log-apply-statusYesYes  GlobalNo
- Variable: ndb_log_apply_status  Yes GlobalNo
ndb_log_apply_statusYesYesYes GlobalNo
ndb_log_binYes Yes BothYes
ndb_log_binlog_indexYes Yes GlobalYes
ndb-log-empty-epochsYesYesYes GlobalYes
ndb_log_empty_epochsYesYesYes GlobalYes
ndb-log-empty-updateYesYesYes GlobalYes
ndb_log_empty_updateYesYesYes GlobalYes
ndb-log-exclusive-readsYesYes  BothYes
- Variable: ndb_log_exclusive_reads  Yes BothYes
ndb_log_exclusive_readsYesYesYes BothYes
ndb-log-origYesYes  GlobalNo
- Variable: ndb_log_orig  Yes GlobalNo
ndb_log_origYesYesYes GlobalNo
ndb-log-transaction-idYesYes  GlobalNo
- Variable: ndb_log_transaction_id  Yes GlobalNo
ndb_log_transaction_id  Yes GlobalNo
ndb_log_updated_onlyYesYesYes GlobalYes
ndb-mgmd-hostYesYes    
ndb-nodeidYesYes YesGlobalNo
Ndb_number_of_data_nodes   YesGlobalNo
ndb_optimization_delay  Yes GlobalYes
ndb_optimized_node_selectionYesYesYes GlobalNo
Ndb_pushed_queries_defined   YesGlobalNo
Ndb_pushed_queries_executed   YesGlobalNo
ndb_read_backupYesYesYes GlobalYes
ndb-recv-thread-activation-thresholdYesYes    
- Variable: ndb_recv_thread_activation_threshold      
ndb_recv_thread_activation_threshold      
ndb-recv-thread-cpu-maskYesYes    
- Variable: ndb_recv_thread_cpu_mask      
ndb_recv_thread_cpu_mask  Yes GlobalYes
ndb_report_thresh_binlog_epoch_slipYesYesYes GlobalYes
ndb_report_thresh_binlog_mem_usageYesYesYes GlobalYes
Ndb_scan_count   YesGlobalNo
ndb_show_foreign_key_mock_tablesYesYesYes GlobalYes
ndb_slave_conflict_roleYesYesYes GlobalYes
Ndb_slave_max_replicated_epoch  Yes GlobalNo
ndb_table_no_logging  Yes SessionYes
ndb_table_temporary  Yes SessionYes
ndb-transid-mysql-connection-mapYes     
ndb_use_copying_alter_table  Yes BothNo
ndb_use_exact_count  Yes BothYes
ndb_use_transactionsYesYesYes BothYes
ndb_version  Yes GlobalNo
ndb_version_string  Yes GlobalNo
ndb-wait-connectedYesYesYes GlobalNo
ndb-wait-setupYesYesYes GlobalNo
ndbclusterYesYes    
ndbinfo_database  Yes GlobalNo
ndbinfo_max_bytesYes Yes BothYes
ndbinfo_max_rowsYes Yes BothYes
ndbinfo_offline  Yes GlobalYes
ndbinfo_show_hiddenYes Yes BothYes
ndbinfo_table_prefixYes Yes BothYes
ndbinfo_version  Yes GlobalNo
net_buffer_lengthYesYesYes BothYes
net_read_timeoutYesYesYes BothYes
net_retry_countYesYesYes BothYes
net_write_timeoutYesYesYes BothYes
newYesYesYes BothYes
ngram_token_sizeYesYesYes GlobalNo
no-defaultsYes     
Not_flushed_delayed_rows   YesGlobalNo
offline_modeYesYesYes GlobalYes
oldYesYesYes GlobalNo
old-alter-tableYesYes  BothYes
- Variable: old_alter_table  Yes BothYes
old_passwords  Yes BothYes
old-style-user-limitsYesYes    
Ongoing_anonymous_gtid_violating_transaction_count   YesGlobalNo
Ongoing_anonymous_transaction_count   YesGlobalNo
Ongoing_automatic_gtid_violating_transaction_count   YesGlobalNo
Open_files   YesGlobalNo
open-files-limitYesYes  GlobalNo
- Variable: open_files_limit  Yes GlobalNo
Open_streams   YesGlobalNo
Open_table_definitions   YesGlobalNo
Open_tables   YesBothNo
Opened_files   YesGlobalNo
Opened_table_definitions   YesBothNo
Opened_tables   YesBothNo
optimizer_prune_levelYesYesYes BothYes
optimizer_search_depthYesYesYes BothYes
optimizer_switchYesYesYes BothYes
optimizer_trace  Yes BothYes
optimizer_trace_features  Yes BothYes
optimizer_trace_limit  Yes BothYes
optimizer_trace_max_mem_size  Yes BothYes
optimizer_trace_offset  Yes BothYes
parser_max_mem_sizeYesYesYes BothYes
partitionYesYes    
performance_schemaYesYesYes GlobalNo
Performance_schema_accounts_lost   YesGlobalNo
performance_schema_accounts_sizeYesYesYes GlobalNo
Performance_schema_cond_classes_lost   YesGlobalNo
Performance_schema_cond_instances_lost   YesGlobalNo
performance-schema-consumer-events-stages-currentYesYes    
performance-schema-consumer-events-stages-historyYesYes    
performance-schema-consumer-events-stages-history-longYesYes    
performance-schema-consumer-events-statements-currentYesYes    
performance-schema-consumer-events-statements-historyYesYes    
performance-schema-consumer-events-statements-history-longYesYes    
performance-schema-consumer-events-transactions-currentYesYes    
performance-schema-consumer-events-transactions-historyYesYes    
performance-schema-consumer-events-transactions-history-longYesYes    
performance-schema-consumer-events-waits-currentYesYes    
performance-schema-consumer-events-waits-historyYesYes    
performance-schema-consumer-events-waits-history-longYesYes    
performance-schema-consumer-global-instrumentationYesYes    
performance-schema-consumer-statements-digestYesYes    
performance-schema-consumer-thread-instrumentationYesYes    
Performance_schema_digest_lost   YesGlobalNo
performance_schema_digests_sizeYesYesYes GlobalNo
performance_schema_events_stages_history_long_sizeYesYesYes GlobalNo
performance_schema_events_stages_history_sizeYesYesYes GlobalNo
performance_schema_events_statements_history_long_sizeYesYesYes GlobalNo
performance_schema_events_statements_history_sizeYesYesYes GlobalNo
performance_schema_events_transactions_history_long_sizeYesYesYes GlobalNo
performance_schema_events_transactions_history_sizeYesYesYes GlobalNo
performance_schema_events_waits_history_long_sizeYesYesYes GlobalNo
performance_schema_events_waits_history_sizeYesYesYes GlobalNo
Performance_schema_file_classes_lost   YesGlobalNo
Performance_schema_file_handles_lost   YesGlobalNo
Performance_schema_file_instances_lost   YesGlobalNo
Performance_schema_hosts_lost   YesGlobalNo
performance_schema_hosts_sizeYesYesYes GlobalNo
Performance_schema_index_stat_lost   YesGlobalNo
performance-schema-instrumentYesYes    
Performance_schema_locker_lost   YesGlobalNo
performance_schema_max_cond_classesYesYesYes GlobalNo
performance_schema_max_cond_instancesYesYesYes GlobalNo
performance_schema_max_digest_lengthYesYesYes GlobalNo
performance_schema_max_file_classesYesYesYes GlobalNo
performance_schema_max_file_handlesYesYesYes GlobalNo
performance_schema_max_file_instancesYesYesYes GlobalNo
performance_schema_max_index_statYesYesYes GlobalNo
performance_schema_max_memory_classesYesYesYes GlobalNo
performance_schema_max_metadata_locksYesYesYes GlobalNo
performance_schema_max_mutex_classesYesYesYes GlobalNo
performance_schema_max_mutex_instancesYesYesYes GlobalNo
performance_schema_max_prepared_statements_instancesYesYesYes GlobalNo
performance_schema_max_program_instancesYesYesYes GlobalNo
performance_schema_max_rwlock_classesYesYesYes GlobalNo
performance_schema_max_rwlock_instancesYesYesYes GlobalNo
performance_schema_max_socket_classesYesYesYes GlobalNo
performance_schema_max_socket_instancesYesYesYes GlobalNo
performance_schema_max_sql_text_lengthYesYesYes GlobalNo
performance_schema_max_stage_classesYesYesYes GlobalNo
performance_schema_max_statement_classesYesYesYes GlobalNo
performance_schema_max_statement_stackYesYesYes GlobalNo
performance_schema_max_table_handlesYesYesYes GlobalNo
performance_schema_max_table_instancesYesYesYes GlobalNo
performance_schema_max_table_lock_statYesYesYes GlobalNo
performance_schema_max_thread_classesYesYesYes GlobalNo
performance_schema_max_thread_instancesYesYesYes GlobalNo
Performance_schema_memory_classes_lost   YesGlobalNo
Performance_schema_metadata_lock_lost   YesGlobalNo
Performance_schema_mutex_classes_lost   YesGlobalNo
Performance_schema_mutex_instances_lost   YesGlobalNo
Performance_schema_nested_statement_lost   YesGlobalNo
Performance_schema_prepared_statements_lost   YesGlobalNo
Performance_schema_program_lost   YesGlobalNo
Performance_schema_rwlock_classes_lost   YesGlobalNo
Performance_schema_rwlock_instances_lost   YesGlobalNo
Performance_schema_session_connect_attrs_lost   YesGlobalNo
performance_schema_session_connect_attrs_sizeYesYesYes GlobalNo
performance_schema_setup_actors_sizeYesYesYes GlobalNo
performance_schema_setup_objects_sizeYesYesYes GlobalNo
Performance_schema_socket_classes_lost   YesGlobalNo
Performance_schema_socket_instances_lost   YesGlobalNo
Performance_schema_stage_classes_lost   YesGlobalNo
Performance_schema_statement_classes_lost   YesGlobalNo
Performance_schema_table_handles_lost   YesGlobalNo
Performance_schema_table_instances_lost   YesGlobalNo
Performance_schema_table_lock_stat_lost   YesGlobalNo
Performance_schema_thread_classes_lost   YesGlobalNo
Performance_schema_thread_instances_lost   YesGlobalNo
Performance_schema_users_lost   YesGlobalNo
performance_schema_users_sizeYesYesYes GlobalNo
pid-fileYesYes  GlobalNo
- Variable: pid_file  Yes GlobalNo
pluginYesYes    
plugin_dirYesYesYes GlobalNo
plugin-loadYesYes    
plugin-load-addYesYes    
portYesYesYes GlobalNo
port-open-timeoutYesYes    
preload_buffer_sizeYesYesYes BothYes
Prepared_stmt_count   YesGlobalNo
print-defaultsYes     
profiling  Yes BothYes
profiling_history_sizeYesYesYes BothYes
protocol_version  Yes GlobalNo
proxy_user  Yes SessionNo
pseudo_slave_mode  Yes SessionYes
pseudo_thread_id  Yes SessionYes
Qcache_free_blocks   YesGlobalNo
Qcache_free_memory   YesGlobalNo
Qcache_hits   YesGlobalNo
Qcache_inserts   YesGlobalNo
Qcache_lowmem_prunes   YesGlobalNo
Qcache_not_cached   YesGlobalNo
Qcache_queries_in_cache   YesGlobalNo
Qcache_total_blocks   YesGlobalNo
Queries   YesBothNo
query_alloc_block_sizeYesYesYes BothYes
query_cache_limitYesYesYes GlobalYes
query_cache_min_res_unitYesYesYes GlobalYes
query_cache_sizeYesYesYes GlobalYes
query_cache_typeYesYesYes BothYes
query_cache_wlock_invalidateYesYesYes BothYes
query_prealloc_sizeYesYesYes BothYes
Questions   YesBothNo
rand_seed1  Yes SessionYes
rand_seed2  Yes SessionYes
range_alloc_block_sizeYesYesYes BothYes
range_optimizer_max_mem_sizeYesYesYes BothYes
rbr_exec_mode  Yes SessionYes
read_buffer_sizeYesYesYes BothYes
read_onlyYesYesYes GlobalYes
read_rnd_buffer_sizeYesYesYes BothYes
relay-logYesYes  GlobalNo
- Variable: relay_log  Yes GlobalNo
relay_log_basename  Yes GlobalNo
relay-log-indexYesYes  GlobalNo
- Variable: relay_log_index  Yes GlobalNo
relay_log_indexYesYesYes GlobalNo
relay-log-info-fileYesYes    
- Variable: relay_log_info_file      
relay_log_info_fileYesYesYes GlobalNo
relay-log-info-repositoryYesYes    
- Variable: relay_log_info_repository      
relay_log_info_repository  Yes GlobalYes
relay_log_purgeYesYesYes GlobalYes
relay-log-recoveryYesYes    
- Variable: relay_log_recovery      
relay_log_recoveryYesYesYes GlobalNo
relay_log_space_limitYesYesYes GlobalNo
removeYes     
replicate-do-dbYesYes    
replicate-do-tableYesYes    
replicate-ignore-dbYesYes    
replicate-ignore-tableYesYes    
replicate-rewrite-dbYesYes    
replicate-same-server-idYesYes    
replicate-wild-do-tableYesYes    
replicate-wild-ignore-tableYesYes    
report-hostYesYes  GlobalNo
- Variable: report_host  Yes GlobalNo
report-passwordYesYes  GlobalNo
- Variable: report_password  Yes GlobalNo
report-portYesYes  GlobalNo
- Variable: report_port  Yes GlobalNo
report-userYesYes  GlobalNo
- Variable: report_user  Yes GlobalNo
require_secure_transportYesYesYes GlobalYes
rewriter_enabled  Yes GlobalYes
Rewriter_number_loaded_rules   YesGlobalNo
Rewriter_number_reloads   YesGlobalNo
Rewriter_number_rewritten_queries   YesGlobalNo
Rewriter_reload_error   YesGlobalNo
rewriter_verbose  Yes GlobalYes
Rpl_semi_sync_master_clients   YesGlobalNo
rpl_semi_sync_master_enabled  Yes GlobalYes
Rpl_semi_sync_master_net_avg_wait_time   YesGlobalNo
Rpl_semi_sync_master_net_wait_time   YesGlobalNo
Rpl_semi_sync_master_net_waits   YesGlobalNo
Rpl_semi_sync_master_no_times   YesGlobalNo
Rpl_semi_sync_master_no_tx   YesGlobalNo
Rpl_semi_sync_master_status   YesGlobalNo
Rpl_semi_sync_master_timefunc_failures   YesGlobalNo
rpl_semi_sync_master_timeout  Yes GlobalYes
rpl_semi_sync_master_trace_level  Yes GlobalYes
Rpl_semi_sync_master_tx_avg_wait_time   YesGlobalNo
Rpl_semi_sync_master_tx_wait_time   YesGlobalNo
Rpl_semi_sync_master_tx_waits   YesGlobalNo
rpl_semi_sync_master_wait_for_slave_count  Yes GlobalYes
rpl_semi_sync_master_wait_no_slave  Yes GlobalYes
rpl_semi_sync_master_wait_point  Yes GlobalYes
Rpl_semi_sync_master_wait_pos_backtraverse   YesGlobalNo
Rpl_semi_sync_master_wait_sessions   YesGlobalNo
Rpl_semi_sync_master_yes_tx   YesGlobalNo
rpl_semi_sync_slave_enabled  Yes GlobalYes
Rpl_semi_sync_slave_status   YesGlobalNo
rpl_semi_sync_slave_trace_level  Yes GlobalYes
rpl_stop_slave_timeoutYesYesYes GlobalYes
Rsa_public_key   YesGlobalNo
safe-user-createYesYes    
secure-authYesYes  GlobalYes
- Variable: secure_auth  Yes GlobalYes
secure-file-privYesYes  GlobalNo
- Variable: secure_file_priv  Yes GlobalNo
Select_full_join   YesBothNo
Select_full_range_join   YesBothNo
Select_range   YesBothNo
Select_range_check   YesBothNo
Select_scan   YesBothNo
server-idYesYes  GlobalYes
- Variable: server_id  Yes GlobalYes
server-id-bitsYesYes  GlobalNo
- Variable: server_id_bits  Yes GlobalNo
server_id_bitsYesYesYes GlobalNo
server_uuid  Yes GlobalNo
session_track_gtidsYesYesYes BothYes
session_track_schemaYesYesYes BothYes
session_track_state_changeYesYesYes BothYes
session_track_system_variablesYesYesYes BothYes
sha256_password_auto_generate_rsa_keysYesYesYes GlobalNo
sha256_password_private_key_path  Yes GlobalNo
sha256_password_proxy_usersYesYesYes GlobalYes
sha256_password_public_key_path  Yes GlobalNo
shared_memoryYesYesYes GlobalNo
shared_memory_base_nameYesYesYes GlobalNo
show_compatibility_56YesYesYes GlobalYes
show_old_temporalsYesYesYes BothYes
show-slave-auth-infoYesYes    
simplified_binlog_gtid_recoveryYesYesYes GlobalNo
skip-character-set-client-handshakeYesYes    
skip-concurrent-insertYesYes    
- Variable: concurrent_insert      
skip-event-schedulerYesYes    
skip_external_lockingYesYesYes GlobalNo
skip-grant-tablesYesYes    
skip-host-cacheYesYes    
skip-name-resolveYesYes  GlobalNo
- Variable: skip_name_resolve  Yes GlobalNo
skip-ndbclusterYesYes    
skip-networkingYesYes  GlobalNo
- Variable: skip_networking  Yes GlobalNo
skip-newYesYes    
skip-partitionYesYes    
skip-show-databaseYesYes  GlobalNo
- Variable: skip_show_database  Yes GlobalNo
skip-slave-startYesYes    
skip-sslYesYes    
skip-stack-traceYesYes    
skip-symbolic-linksYes     
slave_allow_batchingYesYesYes GlobalYes
slave-checkpoint-groupYesYes    
- Variable: slave_checkpoint_group      
slave_checkpoint_groupYesYesYes GlobalYes
slave-checkpoint-periodYesYes    
- Variable: slave_checkpoint_period      
slave_checkpoint_periodYesYesYes GlobalYes
slave_compressed_protocolYesYesYes GlobalYes
slave_exec_modeYesYesYes GlobalYes
Slave_heartbeat_period   YesGlobalNo
Slave_last_heartbeat   YesGlobalNo
slave-load-tmpdirYesYes  GlobalNo
- Variable: slave_load_tmpdir  Yes GlobalNo
slave-max-allowed-packetYesYes    
- Variable: slave_max_allowed_packet      
slave_max_allowed_packet  Yes GlobalYes
slave-net-timeoutYesYes  GlobalYes
- Variable: slave_net_timeout  Yes GlobalYes
Slave_open_temp_tables   YesGlobalNo
slave-parallel-typeYesYes    
- Variable: slave_parallel_type      
slave_parallel_type  Yes GlobalYes
slave-parallel-workersYesYes    
- Variable: slave_parallel_workers      
slave_parallel_workersYes Yes GlobalYes
slave-pending-jobs-size-maxYes     
- Variable: slave_pending_jobs_size_max      
slave_pending_jobs_size_max  Yes GlobalYes
slave_preserve_commit_orderYes Yes GlobalYes
Slave_received_heartbeats   YesGlobalNo
Slave_retried_transactions   YesGlobalNo
slave-rows-search-algorithmsYesYes    
- Variable: slave_rows_search_algorithms      
slave_rows_search_algorithms  Yes GlobalYes
Slave_running   YesGlobalNo
slave-skip-errorsYesYes  GlobalNo
- Variable: slave_skip_errors  Yes GlobalNo
slave-sql-verify-checksumYesYes    
slave_sql_verify_checksum  Yes GlobalYes
slave_transaction_retriesYesYesYes GlobalYes
slave_type_conversionsYesYesYes GlobalNo
Slow_launch_threads   YesBothNo
slow_launch_timeYesYesYes GlobalYes
Slow_queries   YesBothNo
slow-query-logYesYes  GlobalYes
- Variable: slow_query_log  Yes GlobalYes
slow_query_log_fileYesYesYes GlobalYes
slow-start-timeoutYesYes    
socketYesYesYes GlobalNo
sort_buffer_sizeYesYesYes BothYes
Sort_merge_passes   YesBothNo
Sort_range   YesBothNo
Sort_rows   YesBothNo
Sort_scan   YesBothNo
sporadic-binlog-dump-failYesYes    
sql_auto_is_null  Yes BothYes
sql_big_selects  Yes BothYes
sql_buffer_result  Yes BothYes
sql_log_bin  Yes SessionYes
sql_log_off  Yes BothYes
sql-modeYesYes  BothYes
- Variable: sql_mode  Yes BothYes
sql_notes  Yes BothYes
sql_quote_show_create  Yes BothYes
sql_safe_updates  Yes BothYes
sql_select_limit  Yes BothYes
sql_slave_skip_counter  Yes GlobalYes
sql_warnings  Yes BothYes
sslYesYes    
Ssl_accept_renegotiates   YesGlobalNo
Ssl_accepts   YesGlobalNo
ssl-caYesYes  GlobalNo
- Variable: ssl_ca  Yes GlobalNo
Ssl_callback_cache_hits   YesGlobalNo
ssl-capathYesYes  GlobalNo
- Variable: ssl_capath  Yes GlobalNo
ssl-certYesYes  GlobalNo
- Variable: ssl_cert  Yes GlobalNo
Ssl_cipher   YesBothNo
ssl-cipherYesYes  GlobalNo
- Variable: ssl_cipher  Yes GlobalNo
Ssl_cipher_list   YesBothNo
Ssl_client_connects   YesGlobalNo
Ssl_connect_renegotiates   YesGlobalNo
ssl-crlYesYes  GlobalNo
- Variable: ssl_crl  Yes GlobalNo
ssl-crlpathYesYes  GlobalNo
- Variable: ssl_crlpath  Yes GlobalNo
Ssl_ctx_verify_depth   YesGlobalNo
Ssl_ctx_verify_mode   YesGlobalNo
Ssl_default_timeout   YesBothNo
Ssl_finished_accepts   YesGlobalNo
Ssl_finished_connects   YesGlobalNo
ssl-keyYesYes  GlobalNo
- Variable: ssl_key  Yes GlobalNo
Ssl_server_not_after   YesBothNo
Ssl_server_not_before   YesBothNo
Ssl_session_cache_hits   YesGlobalNo
Ssl_session_cache_misses   YesGlobalNo
Ssl_session_cache_mode   YesGlobalNo
Ssl_session_cache_overflows   YesGlobalNo
Ssl_session_cache_size   YesGlobalNo
Ssl_session_cache_timeouts   YesGlobalNo
Ssl_sessions_reused   YesBothNo
Ssl_used_session_cache_entries   YesGlobalNo
Ssl_verify_depth   YesBothNo
Ssl_verify_mode   YesBothNo
Ssl_version   YesBothNo
standaloneYesYes    
storage_engine  Yes BothYes
stored_program_cacheYesYesYes GlobalYes
super-large-pagesYesYes    
super_read_onlyYesYesYes GlobalYes
symbolic-linksYesYes    
sync_binlogYesYesYes GlobalYes
sync_frmYesYesYes GlobalYes
sync_master_infoYesYesYes GlobalYes
sync_relay_logYesYesYes GlobalYes
sync_relay_log_infoYesYesYes GlobalYes
sysdate-is-nowYesYes    
system_time_zone  Yes GlobalNo
table_definition_cache  Yes GlobalYes
Table_locks_immediate   YesGlobalNo
Table_locks_waited   YesGlobalNo
table_open_cache  Yes GlobalYes
Table_open_cache_hits   YesBothNo
table_open_cache_instances  Yes GlobalNo
Table_open_cache_misses   YesBothNo
Table_open_cache_overflows   YesBothNo
tc-heuristic-recoverYesYes    
Tc_log_max_pages_used   YesGlobalNo
Tc_log_page_size   YesGlobalNo
Tc_log_page_waits   YesGlobalNo
temp-poolYesYes    
thread_cache_sizeYesYesYes GlobalYes
thread_concurrencyYesYesYes GlobalNo
thread_handlingYesYesYes GlobalNo
thread_pool_algorithmYesYesYes GlobalNo
thread_pool_high_priority_connectionYesYesYes BothYes
thread_pool_max_unused_threadsYesYesYes GlobalYes
thread_pool_prio_kickup_timerYesYesYes BothYes
thread_pool_sizeYesYesYes GlobalNo
thread_pool_stall_limitYesYesYes GlobalYes
thread_stackYesYesYes GlobalNo
Threads_cached   YesGlobalNo
Threads_connected   YesGlobalNo
Threads_created   YesGlobalNo
Threads_running   YesGlobalNo
time_format  Yes GlobalNo
time_zone  Yes BothYes
timed_mutexesYesYesYes GlobalYes
timestamp  Yes SessionYes
tls_versionYesYesYes GlobalNo
tmp_table_sizeYesYesYes BothYes
tmpdirYesYesYes GlobalNo
transaction_alloc_block_sizeYesYesYes BothYes
transaction_allow_batching  Yes SessionYes
transaction-isolationYesYes    
- Variable: tx_isolation      
transaction_prealloc_sizeYesYesYes BothYes
transaction-read-onlyYesYes    
- Variable: tx_read_only      
transaction_write_set_extractionYes Yes BothYes
tx_isolation  Yes BothYes
tx_read_only  Yes BothYes
unique_checks  Yes BothYes
updatable_views_with_limitYesYesYes BothYes
Uptime   YesGlobalNo
Uptime_since_flush_status   YesGlobalNo
userYesYes    
validate-passwordYesYes    
validate_password_check_user_nameYesYesYes GlobalYes
validate_password_dictionary_file  Yes GlobalVaries
validate_password_dictionary_file_last_parsed   YesGlobalNo
validate_password_dictionary_file_words_count   YesGlobalNo
validate_password_length  Yes GlobalYes
validate_password_mixed_case_count  Yes GlobalYes
validate_password_number_count  Yes GlobalYes
validate_password_policy  Yes GlobalYes
validate_password_special_char_count  Yes GlobalYes
validate_user_plugins  Yes GlobalNo
verboseYesYes    
version  Yes GlobalNo
version_comment  Yes GlobalNo
version_compile_machine  Yes GlobalNo
version_compile_os  Yes GlobalNo
version_tokens_sessionYesYesYes BothYes
version_tokens_session_numberYesYesYes BothNo
wait_timeoutYesYesYes BothYes
warning_count  Yes SessionNo

[a] This option is dynamic, but only the server should set this information. You should not set the value of this variable manually.

[b] This option is dynamic, but only the server should set this information. You should not set the value of this variable manually.


6.1.4 Server Command Options

When you start the mysqld server, you can specify program options using any of the methods described in Section 5.2.3, “Specifying Program Options”. The most common methods are to provide options in an option file or on the command line. However, in most cases it is desirable to make sure that the server uses the same options each time it runs. The best way to ensure this is to list them in an option file. See Section 5.2.6, “Using Option Files”. That section also describes option file format and syntax.

mysqld reads options from the [mysqld] and [server] groups. mysqld_safe reads options from the [mysqld], [server], [mysqld_safe], and [safe_mysqld] groups. mysql.server reads options from the [mysqld] and [mysql.server] groups.

An embedded MySQL server usually reads options from the [server], [embedded], and [xxxxx_SERVER] groups, where xxxxx is the name of the application into which the server is embedded.

mysqld accepts many command options. For a brief summary, execute this command:

mysqld --help

To see the full list, use this command:

mysqld --verbose --help

Some of the items in the list are actually system variables that can be set at server startup. These can be displayed at runtime using the SHOW VARIABLES statement. Some items displayed by the preceding mysqld command do not appear in SHOW VARIABLES output; this is because they are options only and not system variables.

The following list shows some of the most common server options. Additional options are described in other sections:

Some options control the size of buffers or caches. For a given buffer, the server might need to allocate internal data structures. These structures typically are allocated from the total memory allocated to the buffer, and the amount of space required might be platform dependent. This means that when you assign a value to an option that controls a buffer size, the amount of space actually available might differ from the value assigned. In some cases, the amount might be less than the value assigned. It is also possible that the server will adjust a value upward. For example, if you assign a value of 0 to an option for which the minimal value is 1024, the server will set the value to 1024.

Values for buffer sizes, lengths, and stack sizes are given in bytes unless otherwise specified.

Some options take file name values. Unless otherwise specified, the default file location is the data directory if the value is a relative path name. To specify the location explicitly, use an absolute path name. Suppose that the data directory is /var/mysql/data. If a file-valued option is given as a relative path name, it will be located under /var/mysql/data. If the value is an absolute path name, its location is as given by the path name.

You can also set the values of server system variables at server startup by using variable names as options. To assign a value to a server system variable, use an option of the form --var_name=value. For example, --sort_buffer_size=384M sets the sort_buffer_size variable to a value of 384MB.

When you assign a value to a variable, MySQL might automatically correct the value to stay within a given range, or adjust the value to the closest permissible value if only certain values are permitted.

To restrict the maximum value to which a system variable can be set at runtime with the SET statement, specify this maximum by using an option of the form --maximum-var_name=value at server startup.

You can change the values of most system variables at runtime with the SET statement. See Section 14.7.4.1, “SET Syntax for Variable Assignment”.

Section 6.1.5, “Server System Variables”, provides a full description for all variables, and additional information for setting them at server startup and runtime. For information on changing system variables, see Section 6.1.1, “Configuring the Server”.

  • --help, -?

    Command-Line Format--help

    Display a short help message and exit. Use both the --verbose and --help options to see the full message.

  • --allow-suspicious-udfs

    Command-Line Format--allow-suspicious-udfs
    Permitted ValuesTypeboolean
    DefaultFALSE

    This option controls whether user-defined functions that have only an xxx symbol for the main function can be loaded. By default, the option is off and only UDFs that have at least one auxiliary symbol can be loaded; this prevents attempts at loading functions from shared object files other than those containing legitimate UDFs. See Section 28.4.2.6, “UDF Security Precautions”.

  • --ansi

    Command-Line Format--ansi

    Use standard (ANSI) SQL syntax instead of MySQL syntax. For more precise control over the server SQL mode, use the --sql-mode option instead. See Section 1.8, “MySQL Standards Compliance”, and Section 6.1.8, “Server SQL Modes”.

  • --basedir=dir_name, -b dir_name

    Command-Line Format--basedir=dir_name
    System VariableNamebasedir
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name

    The path to the MySQL installation directory. All paths are usually resolved relative to this directory.

  • --big-tables

    Command-Line Format--big-tables
    System VariableNamebig_tables
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Enable large result sets by saving all temporary sets in files. This option prevents most table full errors, but also slows down queries for which in-memory tables would suffice. The server is able to handle large result sets automatically by using memory for small temporary tables and switching to disk tables where necessary.

  • --bind-address=addr

    Command-Line Format--bind-address=addr
    System VariableNamebind_address
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring
    Default*

    The MySQL server listens on a single network socket for TCP/IP connections. This socket is bound to a single address, but it is possible for an address to map onto multiple network interfaces. To specify an address, use the --bind-address=addr option at server startup, where addr is an IPv4 or IPv6 address or a host name. If addr is a host name, the server resolves the name to an IP address and binds to that address.

    The server treats different types of addresses as follows:

    • If the address is *, the server accepts TCP/IP connections on all server host IPv6 and IPv4 interfaces if the server host supports IPv6, or accepts TCP/IP connections on all IPv4 addresses otherwise. Use this address to permit both IPv4 and IPv6 connections on all server interfaces. This value is the default.

    • If the address is 0.0.0.0, the server accepts TCP/IP connections on all server host IPv4 interfaces.

    • If the address is ::, the server accepts TCP/IP connections on all server host IPv4 and IPv6 interfaces.

    • If the address is an IPv4-mapped address, the server accepts TCP/IP connections for that address, in either IPv4 or IPv6 format. For example, if the server is bound to ::ffff:127.0.0.1, clients can connect using --host=127.0.0.1 or --host=::ffff:127.0.0.1.

    • If the address is a regular IPv4 or IPv6 address (such as 127.0.0.1 or ::1), the server accepts TCP/IP connections only for that IPv4 or IPv6 address.

    If you intend to bind the server to a specific address, be sure that the mysql.user grant table contains an account with administrative privileges that you can use to connect to that address. Otherwise, you will not be able to shut down the server. For example, if you bind the server to *, you can connect to it using all existing accounts. But if you bind the server to ::1, it accepts connections only on that address. In that case, first make sure that the 'root'@'::1' account is present in the mysql.user table so you can still connect to the server to shut it down.

  • --binlog-format={ROW|STATEMENT|MIXED}

    Command-Line Format--binlog-format=format
    System VariableNamebinlog_format
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (<= 5.7.6)Typeenumeration
    DefaultSTATEMENT
    Valid ValuesROW
    STATEMENT
    MIXED
    Permitted Values (>= 5.7.7)Typeenumeration
    DefaultROW
    Valid ValuesROW
    STATEMENT
    MIXED

    Specify whether to use row-based, statement-based, or mixed replication. Statement-based is the default in MySQL 5.7. See Section 18.2.1, “Replication Formats”.

    Under some conditions, changing this variable at runtime is not possible, or causes replication to fail. See Section 6.4.4.2, “Setting The Binary Log Format”, for more information.

    Setting the binary logging format without enabling binary logging sets the binlog_format global system variable and logs a warning.

  • --bootstrap

    Deprecated5.7.6
    Command-Line Format--bootstrap

    This option is used by the mysql_install_db program to create the MySQL privilege tables without having to start a full MySQL server.

    Note

    mysql_install_db is deprecated as of MySQL 5.7.6 because its functionality has been integrated into mysqld, the MySQL server. Consequently, the --bootstrap server option that mysql_install_db passes to mysqld is also deprecated. To initialize a MySQL installation as of MySQL 5.7.6, invoke mysqld with the --initialize or --initialize-insecure option. For more information, see Section 2.10.1.1, “Initializing the Data Directory Manually Using mysqld”. mysql_install_db and the --bootstrap server option will be removed in a future MySQL release.

    --bootstrap is mutually exclusive with --daemonize, --initialize, and --initialize-insecure.

    In MySQL 5.7.8 and later global transaction identifiers (GTIDs) are not disabled when --bootstrap is used. Before MySQL 5.7.8, GTIDs were automatically disabled whenever --bootstrap was used (Bug #20980271). See Section 18.1.3, “Replication with Global Transaction Identifiers”.

    When the server operates in bootstap mode, some functionality is unavailable that limits the statements permitted in any file named by the --init-file option. For more information, see the description of that option. In addition, the disabled_storage_engines system variable has no effect.

  • --character-sets-dir=dir_name

    Command-Line Format--character-sets-dir=dir_name
    System VariableNamecharacter_sets_dir
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name

    The directory where character sets are installed. See Section 11.5, “Character Set Configuration”.

  • --character-set-client-handshake

    Command-Line Format--character-set-client-handshake
    Permitted ValuesTypeboolean
    DefaultTRUE

    Do not ignore character set information sent by the client. To ignore client information and use the default server character set, use --skip-character-set-client-handshake; this makes MySQL behave like MySQL 4.0.

  • --character-set-filesystem=charset_name

    Command-Line Format--character-set-filesystem=name
    System VariableNamecharacter_set_filesystem
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring
    Defaultbinary

    The file system character set. This option sets the character_set_filesystem system variable.

  • --character-set-server=charset_name, -C charset_name

    Command-Line Format--character-set-server
    System VariableNamecharacter_set_server
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring
    Defaultlatin1

    Use charset_name as the default server character set. See Section 11.5, “Character Set Configuration”. If you use this option to specify a nondefault character set, you should also use --collation-server to specify the collation.

  • --chroot=dir_name, -r dir_name

    Command-Line Format--chroot=dir_name
    Permitted ValuesTypedirectory name

    Put the mysqld server in a closed environment during startup by using the chroot() system call. This is a recommended security measure. Use of this option somewhat limits LOAD DATA INFILE and SELECT ... INTO OUTFILE.

  • --collation-server=collation_name

    Command-Line Format--collation-server
    System VariableNamecollation_server
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring
    Defaultlatin1_swedish_ci

    Use collation_name as the default server collation. See Section 11.5, “Character Set Configuration”.

  • --console

    Command-Line Format--console
    Platform SpecificWindows

    (Windows only.) Write error log messages to stderr and stdout even if --log-error is specified. mysqld does not close the console window if this option is used.

    If both --log-error and --console are specified, --console takes precedence. The server writes to the console, but not to the log file. (In MySQL 5.5 and 5.6, the precedence is reversed: --log-error causes --console to be ignored.)

  • --core-file

    Command-Line Format--core-file
    Permitted ValuesTypeboolean
    DefaultOFF

    Write a core file if mysqld dies. The name and location of the core file is system dependent. On Linux, a core file named core.pid is written to the current working directory of the process, which for mysqld is the data directory. pid represents the process ID of the server process. On OS X, a core file named core.pid is written to the /cores directory. On Solaris, use the coreadm command to specify where to write the core file and how to name it.

    For some systems, to get a core file you must also specify the --core-file-size option to mysqld_safe. See Section 5.3.2, “mysqld_safe — MySQL Server Startup Script”. On some systems, such as Solaris, you do not get a core file if you are also using the --user option. There might be additional restrictions or limitations. For example, it might be necessary to execute ulimit -c unlimited before starting the server. Consult your system documentation.

  • --daemonize

    Introduced5.7.6
    Command-Line Format--daemonize[={OFF|ON}]
    Permitted ValuesTypeboolean
    DefaultOFF

    This option causes the server to run as a traditional, forking daemon, permitting it to work with operating systems that use systemd for process control. For more information, see Section 2.5.10, “Managing MySQL Server with systemd”.

    --daemonize is mutually exclusive with --bootstrap, --initialize, and --initialize-insecure.

  • --datadir=dir_name, -h dir_name

    Command-Line Format--datadir=dir_name
    System VariableNamedatadir
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name

    The path to the data directory.

  • --debug[=debug_options], -# [debug_options]

    Command-Line Format--debug[=debug_options]
    System VariableNamedebug
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (Unix)Typestring
    Defaultd:t:i:o,/tmp/mysqld.trace
    Permitted Values (Windows)Typestring
    Defaultd:t:i:O,\mysqld.trace

    If MySQL is configured with the -DWITH_DEBUG=1 CMake option, you can use this option to get a trace file of what mysqld is doing. A typical debug_options string is d:t:o,file_name. The default is d:t:i:o,/tmp/mysqld.trace on Unix and d:t:i:O,\mysqld.trace on Windows.

    Using -DWITH_DEBUG=1 to configure MySQL with debugging support enables you to use the --debug="d,parser_debug" option when you start the server. This causes the Bison parser that is used to process SQL statements to dump a parser trace to the server's standard error output. Typically, this output is written to the error log.

    This option may be given multiple times. Values that begin with + or - are added to or subtracted from the previous value. For example, --debug=T --debug=+P sets the value to P:T.

    For more information, see Section 28.5.3, “The DBUG Package”.

  • --debug-sync-timeout[=N]

    Command-Line Format--debug-sync-timeout[=#]
    Permitted ValuesTypeinteger

    Controls whether the Debug Sync facility for testing and debugging is enabled. Use of Debug Sync requires that MySQL be configured with the -DENABLE_DEBUG_SYNC=1 CMake option (see Section 2.9.4, “MySQL Source-Configuration Options”). If Debug Sync is not compiled in, this option is not available. The option value is a timeout in seconds. The default value is 0, which disables Debug Sync. To enable it, specify a value greater than 0; this value also becomes the default timeout for individual synchronization points. If the option is given without a value, the timeout is set to 300 seconds.

    For a description of the Debug Sync facility and how to use synchronization points, see MySQL Internals: Test Synchronization.

  • --default-authentication-plugin=plugin_name

    Removed5.7.2
    Command-Line Format--default-authentication-plugin=plugin_name
    Permitted ValuesTypeenumeration
    Defaultmysql_native_password
    Valid Valuesmysql_native_password
    sha256_password

    This option sets the default authentication plugin. It was removed in MySQL 5.7.2 and replaced by the default_authentication_plugin system variable. The variable is used the same way as the option at server startup, but also enables the default plugin value to be inspected as runtime. For usage details, see the description of default_authentication_plugin.

  • --default-storage-engine=type

    Command-Line Format--default-storage-engine=name
    System VariableNamedefault_storage_engine
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultInnoDB

    Set the default storage engine for tables. See Chapter 16, Alternative Storage Engines. This option sets the storage engine for permanent tables only. To set the storage engine for TEMPORARY tables, set the default_tmp_storage_engine system variable.

    If you disable the default storage engine at server startup, you must set the default engine for both permanent and TEMPORARY tables to a different engine or the server will not start.

  • --default-time-zone=timezone

    Command-Line Format--default-time-zone=name
    Permitted ValuesTypestring

    Set the default server time zone. This option sets the global time_zone system variable. If this option is not given, the default time zone is the same as the system time zone (given by the value of the system_time_zone system variable.

  • --defaults-extra-file=file_name

    Read this option file after the global option file but (on Unix) before the user option file. If the file does not exist or is otherwise inaccessible, an error occurs. file_name is interpreted relative to the current directory if given as a relative path name rather than a full path name. This must be the first option on the command line if it is used.

    For additional information about this option, see Section 5.2.7, “Command-Line Options that Affect Option-File Handling”.

  • --defaults-file=file_name

    Read only the given option file. If the file does not exist or is otherwise inaccessible, an error occurs. file_name is interpreted relative to the current directory if given as a relative path name rather than a full path name.

    Note

    This must be the first option on the command line if it is used, except that if the server is started with the --defaults-file and --install (or --install-manual) options, --install (or --install-manual) must be first.

    For additional information about this option, see Section 5.2.7, “Command-Line Options that Affect Option-File Handling”.

  • --defaults-group-suffix=str

    Read not only the usual option groups, but also groups with the usual names and a suffix of str. For example, mysqld normally reads the [mysqld] group. If the --defaults-group-suffix=_other option is given, mysqld also reads the [mysqld_other] group.

    For additional information about this option, see Section 5.2.7, “Command-Line Options that Affect Option-File Handling”.

  • --delay-key-write[={OFF|ON|ALL}]

    Command-Line Format--delay-key-write[=name]
    System VariableNamedelay_key_write
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultON
    Valid ValuesON
    OFF
    ALL

    Specify how to use delayed key writes. Delayed key writing causes key buffers not to be flushed between writes for MyISAM tables. OFF disables delayed key writes. ON enables delayed key writes for those tables that were created with the DELAY_KEY_WRITE option. ALL delays key writes for all MyISAM tables. See Section 6.1.1, “Configuring the Server”, and Section 16.2.1, “MyISAM Startup Options”.

    Note

    If you set this variable to ALL, you should not use MyISAM tables from within another program (such as another MySQL server or myisamchk) when the tables are in use. Doing so leads to index corruption.

  • --des-key-file=file_name

    Command-Line Format--des-key-file=file_name

    Read the default DES keys from this file. These keys are used by the DES_ENCRYPT() and DES_DECRYPT() functions.

  • --disable-partition-engine-check

    Introduced5.7.17
    Deprecated5.7.17
    Command-Line Format--disable-partition-engine-check

    Whether to disable the startup check for tables with nonnative partitioning.

    As of MySQL 5.7.17, the generic partitioning handler in the MySQL server is deprecated, and is removed in MySQL 8.0, when the storage engine used for a given table is expected to provide its own (native) partitioning handler. Currently, only the InnoDB and NDB storage engines do.

    Use of tables with nonnative partitioning results in an ER_WARN_DEPRECATED_SYNTAX warning. Also, the server performs a check at startup to identify tables that use nonnative partitioning; for any found, the server writes a message to its error log. To disable this check, use the --disable-partition-engine-check option.

    To prepare for migration to MySQL 8.0, any table with nonnative partitioning should be changed to use an engine that provides native partitioning, or be made nonpartitioned. For example, to change a table to InnoDB, execute this statement:

    ALTER TABLE table_name ENGINE = INNODB;
    
  • --early-plugin-load=plugin_list

    Introduced5.7.11
    Command-Line Format--early-plugin-load=plugin_list
    Permitted Values (5.7.11)Typestring
    Defaultkeyring_file plugin library file name
    Permitted Values (>= 5.7.12)Typestring
    Defaultempty string

    This option tells the server which plugins to load before loading mandatory built-in plugins and before storage engine initialization. If multiple --early-plugin-load options are given, only the last one is used.

    The option value is a semicolon-separated list of name=plugin_library and plugin_library values. Each name is the name of a plugin to load, and plugin_library is the name of the library file that contains the plugin code. If a plugin library is named without any preceding plugin name, the server loads all plugins in the library. The server looks for plugin library files in the directory named by the plugin_dir system variable.

    For example, if plugins named myplug1 and myplug2 have library files myplug1.so and myplug2.so, use this option to perform an early plugin load:

    shell> mysqld --early-plugin-load="myplug1=myplug1.so;myplug2=myplug2.so"
    

    Quotes are used around the argument value because otherwise a semicolon (;) is interpreted as a special character by some command interpreters. (Unix shells treat it as a command terminator, for example.)

    Each named plugin is loaded early for a single invocation of mysqld only. After a restart, the plugin is not loaded early unless --early-plugin-load is used again.

    If the server is started using --initialize or --initialize-insecure, plugins specified by --early-plugin-load are not loaded.

    If the server is run with --help, plugins specified by --early-plugin-load are loaded but not initialized. This behavior ensures that plugin options are displayed in the help message.

    As of MySQL 5.7.12, the default --early-plugin-load value is empty. To load your chosen keyring plugin, you must use an explicit --early-plugin-load option with a nonempty value.

    Important

    In MySQL 5.7.11, the default --early-plugin-load value was the name of the keyring_file plugin library file, so that plugin was loaded by default. InnoDB tablespace encryption requires the keyring_file plugin to be loaded prior to InnoDB initialization, so this change of default --early-plugin-load value introduces an incompatibility for upgrades from 5.7.11 to 5.7.12 or higher. Administrators who have encrypted InnoDB tablespaces must take explicit action to ensure continued loading of the keyring_file plugin: Start the server with an --early-plugin-load option that names the plugin library file. For additional information, see Section 7.5.4.1, “Keyring Plugin Installation”.

    The InnoDB tablespace encryption feature relies on the keyring_file plugin for encryption key management, and the keyring_file plugin must be loaded prior to storage engine initialization to facilitate InnoDB recovery for encrypted tables. In MySQL 5.7.11, if you do not want to load the keyring_file plugin at server startup, specify an empty string (--early-plugin-load="").

    For information about InnoDB tablespace encryption, see Section 15.7.10, “InnoDB Tablespace Encryption”. For general information about plugin loading, see Section 6.5.2, “Installing and Uninstalling Plugins”.

  • --enable-named-pipe

    Command-Line Format--enable-named-pipe
    Platform SpecificWindows

    Enable support for named pipes. This option applies only on Windows.

  • --event-scheduler[=value]

    Command-Line Format--event-scheduler[=value]
    System VariableNameevent_scheduler
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultOFF
    Valid ValuesON
    OFF
    DISABLED

    Enable or disable, and start or stop, the event scheduler.

    For detailed information, see The --event-scheduler Option.

  • --exit-info[=flags], -T [flags]

    Command-Line Format--exit-info[=flags]
    Permitted ValuesTypeinteger

    This is a bitmask of different flags that you can use for debugging the mysqld server. Do not use this option unless you know exactly what it does!

  • --external-locking

    Command-Line Format--external-locking
    Permitted ValuesTypeboolean
    DefaultFALSE

    Enable external locking (system locking), which is disabled by default. If you use this option on a system on which lockd does not fully work (such as Linux), it is easy for mysqld to deadlock.

    To disable external locking explicitly, use --skip-external-locking.

    External locking affects only MyISAM table access. For more information, including conditions under which it can and cannot be used, see Section 9.11.5, “External Locking”.

  • --flush

    Command-Line Format--flush
    System VariableNameflush
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Flush (synchronize) all changes to disk after each SQL statement. Normally, MySQL does a write of all changes to disk only after each SQL statement and lets the operating system handle the synchronizing to disk. See Section B.5.3.3, “What to Do If MySQL Keeps Crashing”.

  • --gdb

    Command-Line Format--gdb
    Permitted ValuesTypeboolean
    DefaultFALSE

    Install an interrupt handler for SIGINT (needed to stop mysqld with ^C to set breakpoints) and disable stack tracing and core file handling. See Section 28.5, “Debugging and Porting MySQL”.

  • --general-log[={0|1}]

    Command-Line Format--general-log
    System VariableNamegeneral_log
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Specify the initial general query log state. With no argument or an argument of 1, the --general-log option enables the log. If omitted or given with an argument of 0, the option disables the log.

  • --ignore-db-dir=dir_name

    Command-Line Format--ignore-db-dir
    Permitted ValuesTypedirectory name

    This option tells the server to ignore the given directory name for purposes of the SHOW DATABASES statement or INFORMATION_SCHEMA tables. For example, if a MySQL configuration locates the data directory at the root of a file system on Unix, the system might create a lost+found directory there that the server should ignore. Starting the server with --ignore-db-dir=lost+found causes that name not to be listed as a database.

    To specify more than one name, use this option multiple times, once for each name. Specifying the option with an empty value (that is, as --ignore-db-dir=) resets the directory list to the empty list.

    Instances of this option given at server startup are used to set the ignore_db_dirs system variable.

  • --initialize

    Introduced5.7.6
    Command-Line Format--initialize
    Permitted ValuesTypeboolean
    DefaultOFF

    This option is used to initialize a MySQL installation by creating the data directory and populating the tables in the mysql system database. For more information, see Section 2.10.1.1, “Initializing the Data Directory Manually Using mysqld”.

    When the server is started with --initialize, some functionality is unavailable that limits the statements permitted in any file named by the --init-file option. For more information, see the description of that option. In addition, the disabled_storage_engines system variable has no effect.

    In MySQL NDB Cluster 7.5.4 and later, the --ndbcluster option is ignored when used together with --initialize. (Bug #81689, Bug #23518923)

    In MySQL 5.7.7 and earlier, global transaction identifiers (GTIDs) were automatically disabled whenever --initialize was enabled. In MySQL 5.7.8 and later GTIDs are not disabled when --initialize is enabled.

    --initialize is mutually exclusive with --bootstrap and --daemonize.

  • --initialize-insecure

    Introduced5.7.6
    Command-Line Format--initialize-insecure
    Permitted ValuesTypeboolean
    DefaultOFF

    This option is used to initialize a MySQL installation by creating the data directory and populating the tables in the mysql system database. This option implies --initialize. For more information, see the description of that option, and Section 2.10.1.1, “Initializing the Data Directory Manually Using mysqld”.

    --initialize-insecure is mutually exclusive with --bootstrap and --daemonize.

  • --init-file=file_name

    Command-Line Format--init-file=file_name
    System VariableNameinit_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name

    Read SQL statements from this file at startup. Each statement must be on a single line and should not include comments.

    If the server is started with any of the --bootstrap, --initialize, or --initialize-insecure options, it operates in bootstap mode and some functionality is unavailable that limits the statements permitted in the file. These include statements that relate to account management (such as CREATE USER or GRANT), replication, and global transaction identifiers. See Section 18.1.3, “Replication with Global Transaction Identifiers”.

  • --innodb-xxx

    Set an option for the InnoDB storage engine. The InnoDB options are listed in Section 15.14, “InnoDB Startup Options and System Variables”.

  • --install [service_name]

    Command-Line Format--install [service_name]
    Platform SpecificWindows

    (Windows only) Install the server as a Windows service that starts automatically during Windows startup. The default service name is MySQL if no service_name value is given. For more information, see Section 2.3.5.8, “Starting MySQL as a Windows Service”.

    Note

    If the server is started with the --defaults-file and --install options, --install must be first.

  • --install-manual [service_name]

    Command-Line Format--install-manual [service_name]
    Platform SpecificWindows

    (Windows only) Install the server as a Windows service that must be started manually. It does not start automatically during Windows startup. The default service name is MySQL if no service_name value is given. For more information, see Section 2.3.5.8, “Starting MySQL as a Windows Service”.

    Note

    If the server is started with the --defaults-file and --install-manual options, --install-manual must be first.

  • --language=lang_name, -L lang_name

    Deprecated5.6.1, by lc-messages-dir
    Command-Line Format--language=name
    System VariableNamelanguage
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name
    Default/usr/local/mysql/share/mysql/english/

    The language to use for error messages. lang_name can be given as the language name or as the full path name to the directory where the language files are installed. See Section 11.2, “Setting the Error Message Language”.

    --lc-messages-dir and --lc-messages should be used rather than --language, which is deprecated (and handled as an alias for --lc-messages-dir). The --language option will be removed in a future MySQL release.

  • --large-pages

    Command-Line Format--large-pages
    System VariableNamelarge_pages
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform SpecificLinux
    Permitted Values (Linux)Typeboolean
    DefaultFALSE

    Some hardware/operating system architectures support memory pages greater than the default (usually 4KB). The actual implementation of this support depends on the underlying hardware and operating system. Applications that perform a lot of memory accesses may obtain performance improvements by using large pages due to reduced Translation Lookaside Buffer (TLB) misses.

    MySQL supports the Linux implementation of large page support (which is called HugeTLB in Linux). See Section 9.12.4.2, “Enabling Large Page Support”. For Solaris support of large pages, see the description of the --super-large-pages option.

    --large-pages is disabled by default.

  • --lc-messages=locale_name

    Command-Line Format--lc-messages=name
    System VariableNamelc_messages
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring
    Defaulten_US

    The locale to use for error messages. The default is en_US. The server converts the argument to a language name and combines it with the value of --lc-messages-dir to produce the location for the error message file. See Section 11.2, “Setting the Error Message Language”.

  • --lc-messages-dir=dir_name

    Command-Line Format--lc-messages-dir=dir_name
    System VariableNamelc_messages_dir
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name

    The directory where error messages are located. The server uses the value together with the value of --lc-messages to produce the location for the error message file. See Section 11.2, “Setting the Error Message Language”.

  • --local-service

    Command-Line Format--local-service

    (Windows only) A --local-service option following the service name causes the server to run using the LocalService Windows account that has limited system privileges. If both --defaults-file and --local-service are given following the service name, they can be in any order. See Section 2.3.5.8, “Starting MySQL as a Windows Service”.

  • --log-error[=file_name]

    Command-Line Format--log-error[=file_name]
    System VariableNamelog_error
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name

    Log errors and startup messages to this file. See Section 6.4.2, “The Error Log”. If the file name has no extension, the server adds an extension of .err. If you omit the file name, the default log file on Unix and Unix-like systems is host_name.err in the data directory. The default on Windows is host_name.err in the data directory, unless the --pid-file option is specified. In that case, the default name is the PID file base name with a suffix of .err in the data directory.

  • --log-isam[=file_name]

    Command-Line Format--log-isam[=file_name]
    Permitted ValuesTypefile name

    Log all MyISAM changes to this file (used only when debugging MyISAM).

  • --log-output=value,...

    Command-Line Format--log-output=name
    System VariableNamelog_output
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeset
    DefaultFILE
    Valid ValuesTABLE
    FILE
    NONE

    This option determines the destination for general query log and slow query log output. The option value can be given as one or more of the words TABLE, FILE, or NONE. TABLE select logging to the general_log and slow_log tables in the mysql database as a destination. FILE selects logging to log files as a destination. NONE disables logging. If NONE is present in the option value, it takes precedence over any other words that are present. TABLE and FILE can both be given to select to both log output destinations.

    This option selects log output destinations, but does not enable log output. To do that, use the --general_log and --slow_query_log options. For FILE logging, the --general_log_file and -slow_query_log_file options determine the log file location. For more information, see Section 6.4.1, “Selecting General Query and Slow Query Log Output Destinations”.

  • --log-queries-not-using-indexes

    Command-Line Format--log-queries-not-using-indexes
    System VariableNamelog_queries_not_using_indexes
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    If you are using this option with the slow query log enabled, queries that are expected to retrieve all rows are logged. See Section 6.4.5, “The Slow Query Log”. This option does not necessarily mean that no index is used. For example, a query that uses a full index scan uses an index but would be logged because the index would not limit the number of rows.

  • --log-raw

    Command-Line Format--log-raw[=value]
    Permitted ValuesTypeboolean
    DefaultOFF

    Passwords in certain statements written to the general query log, slow query log, and binary log are rewritten by the server not to occur literally in plain text. Password rewriting can be suppressed for the general query log by starting the server with the --log-raw option. This option may be useful for diagnostic purposes, to see the exact text of statements as received by the server, but for security reasons is not recommended for production use.

    If a query rewrite plugin is installed, the --log-raw option affects statement logging as follows:

    • Without --log-raw, the server logs the statement returned by the query rewrite plugin. This may differ from the statement as received.

    • With --log-raw, the server logs the original statement as received.

    For more information, see Section 7.1.2.3, “Passwords and Logging”.

  • --log-short-format

    Command-Line Format--log-short-format
    Permitted ValuesTypeboolean
    DefaultFALSE

    Log less information to the slow query log, if it has been activated.

  • --log-slow-admin-statements

    Removed5.7.1
    Command-Line Format--log-slow-admin-statements (5.7.0)
    Permitted ValuesTypeboolean
    DefaultOFF

    Include slow administrative statements in the statements written to the slow query log. Administrative statements include ALTER TABLE, ANALYZE TABLE, CHECK TABLE, CREATE INDEX, DROP INDEX, OPTIMIZE TABLE, and REPAIR TABLE.

    This command-line option was removed in MySQL 5.7.1 and replaced by the log_slow_admin_statements system variable. The system variable can be set on the command line or in option files the same way as the option, so there is no need for any changes at server startup, but the system variable also makes it possible to examine or set the value at runtime.

  • --log-tc=file_name

    Command-Line Format--log-tc=file_name
    Permitted ValuesTypefile name
    Defaulttc.log

    The name of the memory-mapped transaction coordinator log file (for XA transactions that affect multiple storage engines when the binary log is disabled). The default name is tc.log. The file is created under the data directory if not given as a full path name. This option is unused.

  • --log-tc-size=size

    Command-Line Format--log-tc-size=#
    Permitted Values (32-bit platforms)Typeinteger
    Default24576
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default24576
    Max Value18446744073709551615

    The size in bytes of the memory-mapped transaction coordinator log. The default size is 24KB.

  • --log-warnings[=level], -W [level]

    Deprecated5.7.2
    Command-Line Format--log-warnings[=#]
    System VariableNamelog_warnings
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms, <= 5.7.1)Typeinteger
    Default1
    Min Value0
    Max Value4294967295
    Permitted Values (32-bit platforms, >= 5.7.2)Typeinteger
    Default2
    Min Value0
    Max Value4294967295
    Permitted Values (64-bit platforms, <= 5.7.1)Typeinteger
    Default1
    Min Value0
    Max Value18446744073709551615
    Permitted Values (64-bit platforms, >= 5.7.2)Typeinteger
    Default2
    Min Value0
    Max Value18446744073709551615
    Note

    As of MySQL 5.7.2, the log_error_verbosity system variable is preferred over, and should be used instead of, the --log-warnings option or log_warnings system variable. For more information, see the descriptions of log_error_verbosity and log_warnings. The --log-warnings command-line option and log_warnings system variable are deprecated and will be removed in a future MySQL release.

    Whether to produce additional warning messages to the error log. This option is enabled by default (the default is 1 before MySQL 5.7.2, 2 as of 5.7.2). To disable it, use --log-warnings=0. Specifying the option without a level value increments the current value by 1. The server logs messages about statements that are unsafe for statement-based logging if the value is greater than 0. Aborted connections and access-denied errors for new connection attempts are logged if the value is greater than 1. See Section B.5.2.11, “Communication Errors and Aborted Connections”.

  • --low-priority-updates

    Command-Line Format--low-priority-updates
    System VariableNamelow_priority_updates
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultFALSE

    Give table-modifying operations (INSERT, REPLACE, DELETE, UPDATE) lower priority than selects. This can also be done using {INSERT | REPLACE | DELETE | UPDATE} LOW_PRIORITY ... to lower the priority of only one query, or by SET LOW_PRIORITY_UPDATES=1 to change the priority in one thread. This affects only storage engines that use only table-level locking (MyISAM, MEMORY, MERGE). See Section 9.11.2, “Table Locking Issues”.

  • --min-examined-row-limit=number

    Command-Line Format--min-examined-row-limit=#
    System VariableNamemin_examined_row_limit
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default0
    Min Value0
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default0
    Min Value0
    Max Value18446744073709551615

    When this option is set, queries which examine fewer than number rows are not written to the slow query log. The default is 0.

  • --memlock

    Command-Line Format--memlock
    Permitted ValuesTypeboolean
    DefaultFALSE

    Lock the mysqld process in memory. This option might help if you have a problem where the operating system is causing mysqld to swap to disk.

    --memlock works on systems that support the mlockall() system call; this includes Solaris, most Linux distributions that use a 2.4 or higher kernel, and perhaps other Unix systems. On Linux systems, you can tell whether or not mlockall() (and thus this option) is supported by checking to see whether or not it is defined in the system mman.h file, like this:

    shell> grep mlockall /usr/include/sys/mman.h
    

    If mlockall() is supported, you should see in the output of the previous command something like the following:

    extern int mlockall (int __flags) __THROW;
    
    Important

    Use of this option may require you to run the server as root, which, for reasons of security, is normally not a good idea. See Section 7.1.5, “How to Run MySQL as a Normal User”.

    On Linux and perhaps other systems, you can avoid the need to run the server as root by changing the limits.conf file. See the notes regarding the memlock limit in Section 9.12.4.2, “Enabling Large Page Support”.

    You must not try to use this option on a system that does not support the mlockall() system call; if you do so, mysqld will very likely crash as soon as you try to start it.

  • --myisam-block-size=N

    Command-Line Format--myisam-block-size=#
    Permitted ValuesTypeinteger
    Default1024
    Min Value1024
    Max Value16384

    The block size to be used for MyISAM index pages.

  • --myisam-recover-options[=option[,option]...]]

    Command-Line Format--myisam-recover-options[=name]
    Permitted ValuesTypeenumeration
    DefaultOFF
    Valid ValuesOFF
    DEFAULT
    BACKUP
    FORCE
    QUICK

    Set the MyISAM storage engine recovery mode. The option value is any combination of the values of OFF, DEFAULT, BACKUP, FORCE, or QUICK. If you specify multiple values, separate them by commas. Specifying the option with no argument is the same as specifying DEFAULT, and specifying with an explicit value of "" disables recovery (same as a value of OFF). If recovery is enabled, each time mysqld opens a MyISAM table, it checks whether the table is marked as crashed or was not closed properly. (The last option works only if you are running with external locking disabled.) If this is the case, mysqld runs a check on the table. If the table was corrupted, mysqld attempts to repair it.

    The following options affect how the repair works.

    OptionDescription
    OFFNo recovery.
    DEFAULTRecovery without backup, forcing, or quick checking.
    BACKUPIf the data file was changed during recovery, save a backup of the tbl_name.MYD file as tbl_name-datetime.BAK.
    FORCERun recovery even if we would lose more than one row from the .MYD file.
    QUICKDo not check the rows in the table if there are not any delete blocks.

    Before the server automatically repairs a table, it writes a note about the repair to the error log. If you want to be able to recover from most problems without user intervention, you should use the options BACKUP,FORCE. This forces a repair of a table even if some rows would be deleted, but it keeps the old data file as a backup so that you can later examine what happened.

    See Section 16.2.1, “MyISAM Startup Options”.

  • --no-defaults

    Do not read any option files. If program startup fails due to reading unknown options from an option file, --no-defaults can be used to prevent them from being read. This must be the first option on the command line if it is used.

    For additional information about this option, see Section 5.2.7, “Command-Line Options that Affect Option-File Handling”.

  • --old-alter-table

    Command-Line Format--old-alter-table
    System VariableNameold_alter_table
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    When this option is given, the server does not use the optimized method of processing an ALTER TABLE operation. It reverts to using a temporary table, copying over the data, and then renaming the temporary table to the original, as used by MySQL 5.0 and earlier. For more information on the operation of ALTER TABLE, see Section 14.1.8, “ALTER TABLE Syntax”.

  • --old-style-user-limits

    Command-Line Format--old-style-user-limits
    Permitted ValuesTypeboolean
    DefaultFALSE

    Enable old-style user limits. (Before MySQL 5.0.3, account resource limits were counted separately for each host from which a user connected rather than per account row in the user table.) See Section 7.3.4, “Setting Account Resource Limits”.

  • --open-files-limit=count

    Command-Line Format--open-files-limit=#
    System VariableNameopen_files_limit
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default5000, with possible adjustment
    Min Value0
    Max Valueplatform dependent

    Changes the number of file descriptors available to mysqld. You should try increasing the value of this option if mysqld gives you the error Too many open files. mysqld uses the option value to reserve descriptors with setrlimit(). Internally, the maximum value for this option is the maximum unsigned integer value, but the actual maximum is platform dependent. If the requested number of file descriptors cannot be allocated, mysqld writes a warning to the error log.

    mysqld may attempt to allocate more than the requested number of descriptors (if they are available), using the values of max_connections and table_open_cache to estimate whether more descriptors will be needed.

    On Unix, the value cannot be set less than ulimit -n.

  • --partition[=value]

    Deprecated5.7.16
    Command-Line Format--partition
    Disabled byskip-partition
    Permitted ValuesTypeboolean
    DefaultON

    Enables or disables user-defined partitioning support in the MySQL Server.

    This option is deprecated in MySQL 5.7.16, and is removed from MySQL 8.0.

  • --performance-schema-xxx

    Configure a Performance Schema option. For details, see Section 25.12, “Performance Schema Command Options”.

  • --pid-file=file_name

    Command-Line Format--pid-file=file_name
    System VariableNamepid_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name

    The path name of the process ID file. The server creates the file in the data directory unless an absolute path name is given to specify a different directory. This file is used by other programs such as mysqld_safe to determine the server's process ID.

  • --plugin-xxx

    Specifies an option that pertains to a server plugin. For example, many storage engines can be built as plugins, and for such engines, options for them can be specified with a --plugin prefix. Thus, the --innodb_file_per_table option for InnoDB can be specified as --plugin-innodb_file_per_table.

    For boolean options that can be enabled or disabled, the --skip prefix and other alternative formats are supported as well (see Section 5.2.5, “Program Option Modifiers”). For example, --skip-plugin-innodb_file_per_table disables innodb_file_per_table.

    The rationale for the --plugin prefix is that it enables plugin options to be specified unambiguously if there is a name conflict with a built-in server option. For example, were a plugin writer to name a plugin sql and implement a mode option, the option name might be --sql-mode, which would conflict with the built-in option of the same name. In such cases, references to the conflicting name are resolved in favor of the built-in option. To avoid the ambiguity, users can specify the plugin option as --plugin-sql-mode. Use of the --plugin prefix for plugin options is recommended to avoid any question of ambiguity.

  • --plugin-load=plugin_list

    Command-Line Format--plugin-load=plugin_list
    Permitted ValuesTypestring

    This option tells the server to load the named plugins at startup. If multiple --plugin-load options are given, only the last one is used. Additional plugins to load may be specified using --plugin-load-add options.

    The option value is a semicolon-separated list of name=plugin_library and plugin_library values. Each name is the name of a plugin to load, and plugin_library is the name of the library file that contains the plugin code. If a plugin library is named without any preceding plugin name, the server loads all plugins in the library. The server looks for plugin library files in the directory named by the plugin_dir system variable.

    For example, if plugins named myplug1 and myplug2 have library files myplug1.so and myplug2.so, use this option to perform an early plugin load:

    shell> mysqld --plugin-load="myplug1=myplug1.so;myplug2=myplug2.so"
    

    Quotes are used around the argument value here because otherwise semicolon (;) is interpreted as a special character by some command interpreters. (Unix shells treat it as a command terminator, for example.)

    Each named plugin is loaded for a single invocation of mysqld only. After a restart, the plugin is not loaded unless --plugin-load is used again. This is in contrast to INSTALL PLUGIN, which adds an entry to the mysql.plugins table to cause the plugin to be loaded for every normal server startup.

    Under normal startup, the server determines which plugins to load by reading the mysql.plugins system table. If the server is started with the --skip-grant-tables option, it does not consult the mysql.plugins table and does not load plugins listed there. --plugin-load enables plugins to be loaded even when --skip-grant-tables is given. --plugin-load also enables plugins to be loaded at startup that cannot be loaded at runtime.

    For additional information about plugin loading, see Section 6.5.2, “Installing and Uninstalling Plugins”.

  • --plugin-load-add=plugin_list

    Command-Line Format--plugin-load-add=plugin_list
    Permitted ValuesTypestring

    This option complements the --plugin-load option. --plugin-load-add adds a plugin or plugins to the set of plugins to be loaded at startup. The argument format is the same as for --plugin-load. --plugin-load-add can be used to avoid specifying a large set of plugins as a single long unwieldy --plugin-load argument.

    --plugin-load-add can be given in the absence of --plugin-load, but any instance of --plugin-load-add that appears before --plugin-load. has no effect because --plugin-load resets the set of plugins to load. In other words, these options:

    --plugin-load=x --plugin-load-add=y
    

    are equivalent to this option:

    --plugin-load="x;y"
    

    But these options:

    --plugin-load-add=y --plugin-load=x
    

    are equivalent to this option:

    --plugin-load=x
    

    For additional information about plugin loading, see Section 6.5.2, “Installing and Uninstalling Plugins”.

  • --port=port_num, -P port_num

    Command-Line Format--port=#
    System VariableNameport
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default3306
    Min Value0
    Max Value65535

    The port number to use when listening for TCP/IP connections. On Unix and Unix-like systems, the port number must be 1024 or higher unless the server is started by the root system user.

  • --port-open-timeout=num

    Command-Line Format--port-open-timeout=#
    Permitted ValuesTypeinteger
    Default0

    On some systems, when the server is stopped, the TCP/IP port might not become available immediately. If the server is restarted quickly afterward, its attempt to reopen the port can fail. This option indicates how many seconds the server should wait for the TCP/IP port to become free if it cannot be opened. The default is not to wait.

  • --print-defaults

    Print the program name and all options that it gets from option files. Password values are masked. This must be the first option on the command line if it is used, except that it may be used immediately after --defaults-file or --defaults-extra-file.

    For additional information about this option, see Section 5.2.7, “Command-Line Options that Affect Option-File Handling”.

  • --remove [service_name]

    Command-Line Format--remove [service_name]
    Platform SpecificWindows

    (Windows only) Remove a MySQL Windows service. The default service name is MySQL if no service_name value is given. For more information, see Section 2.3.5.8, “Starting MySQL as a Windows Service”.

  • --safe-user-create

    Command-Line Format--safe-user-create
    Permitted ValuesTypeboolean
    DefaultFALSE

    If this option is enabled, a user cannot create new MySQL users by using the GRANT statement unless the user has the INSERT privilege for the mysql.user table or any column in the table. If you want a user to have the ability to create new users that have those privileges that the user has the right to grant, you should grant the user the following privilege:

    GRANT INSERT(user) ON mysql.user TO 'user_name'@'host_name';
    

    This ensures that the user cannot change any privilege columns directly, but has to use the GRANT statement to give privileges to other users.

  • --secure-auth

    Deprecated5.7.5
    Command-Line Format--secure-auth
    System VariableNamesecure_auth
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (<= 5.7.4)Typeboolean
    DefaultON
    Valid ValuesOFF
    ON
    Permitted Values (>= 5.7.5)Typeboolean
    DefaultON
    Valid ValuesON

    This option causes the server to block connections by clients that attempt to use accounts that have passwords stored in the old (pre-4.1) format. Use it to prevent all use of passwords employing the old format (and hence insecure communication over the network).

    As of MySQL 5.7.5, this option is deprecated and will be removed in a future MySQL release. It is always enabled and attempting to disable it (--skip-secure-auth, --secure-auth=0) produces an error. Before MySQL 5.7.5, this option is enabled by default but can be disabled.

    Server startup fails with an error if this option is enabled and the privilege tables are in pre-4.1 format. See Section B.5.2.4, “Client does not support authentication protocol”.

    The mysql client also has a --secure-auth option, which prevents connections to a server if the server requires a password in old format for the client account.

    Note

    Passwords that use the pre-4.1 hashing method are less secure than passwords that use the native password hashing method and should be avoided. Pre-4.1 passwords are deprecated and support for them is removed in MySQL 5.7.5. For account upgrade instructions, see Section 7.5.1.3, “Migrating Away from Pre-4.1 Password Hashing and the mysql_old_password Plugin”.

  • --secure-file-priv=dir_name

    Command-Line Format--secure-file-priv=dir_name
    System VariableNamesecure_file_priv
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted Values (<= 5.7.5)Typestring
    Defaultempty
    Valid Valuesempty
    dirname
    Permitted Values (>= 5.7.6)Typestring
    Defaultplatform specific
    Valid Valuesempty
    dirname
    NULL

    This option sets the secure_file_priv system variable, which is used to limit the effect of data import and export operations, such as those performed by the LOAD DATA and SELECT ... INTO OUTFILE statements and the LOAD_FILE() function. For more information, see the description of secure_file_priv.

  • --shared-memory

    Command-Line Format--shared_memory[={0,1}]
    System VariableNameshared_memory
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform SpecificWindows
    Permitted ValuesTypeboolean
    DefaultFALSE

    Enable shared-memory connections by local clients. This option is available only on Windows.

  • --shared-memory-base-name=name

    Command-Line Format--shared_memory_base_name=name
    System VariableNameshared_memory_base_name
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform SpecificWindows
    Permitted ValuesTypestring
    DefaultMYSQL

    The name of shared memory to use for shared-memory connections. This option is available only on Windows. The default name is MYSQL. The name is case sensitive.

  • --skip-concurrent-insert

    Turn off the ability to select and insert at the same time on MyISAM tables. (This is to be used only if you think you have found a bug in this feature.) See Section 9.11.3, “Concurrent Inserts”.

  • --skip-event-scheduler

    Command-Line Format--skip-event-scheduler
     --disable-event-scheduler

    Turns the Event Scheduler OFF. This is not the same as disabling the Event Scheduler, which requires setting --event-scheduler=DISABLED; see The --event-scheduler Option, for more information.

  • --skip-grant-tables

    This option causes the server to start without using the privilege system at all, which gives anyone with access to the server unrestricted access to all databases. You can cause a running server to start using the grant tables again by executing mysqladmin flush-privileges or mysqladmin reload command from a system shell, or by issuing a MySQL FLUSH PRIVILEGES statement after connecting to the server.

    This option also causes the server to suppress during its startup sequence the loading of user-defined functions (UDFs), scheduled events, and plugins that were installed with the INSTALL PLUGIN statement. To cause plugins to be loaded anyway, use the --plugin-load option. --skip-grant-tables also causes the disabled_storage_engines system variable to have no effect.

    FLUSH PRIVILEGES might be executed implicitly by other actions performed after startup. For example, mysql_upgrade flushes the privileges during the upgrade procedure.

  • --skip-host-cache

    Disable use of the internal host cache for faster name-to-IP resolution. In this case, the server performs a DNS lookup every time a client connects. See Section 9.12.5.2, “DNS Lookup Optimization and the Host Cache”.

    Use of --skip-host-cache is similar to setting the host_cache_size system variable to 0, but host_cache_size is more flexible because it can also be used to resize, enable, or disable the host cache at runtime, not just at server startup.

    If you start the server with --skip-host-cache, that does not prevent changes to the value of host_cache_size, but such changes have no effect and the cache is not re-enabled even if host_cache_size is set larger than 0.

  • --skip-innodb

    Disable the InnoDB storage engine. In this case, because the default storage engine is InnoDB, the server will not start unless you also use --default-storage-engine and --default-tmp-storage-engine to set the default to some other engine for both permanent and TEMPORARY tables.

    As of MySQL 5.7.5, the InnoDB storage engine can no longer be disabled, and the --skip-innodb option is deprecated and has no effect. Its use results in a warning. This option will be removed in a future MySQL release.

  • --skip-name-resolve

    Do not resolve host names when checking client connections. Use only IP addresses. If you use this option, all Host column values in the grant tables must be IP addresses. See Section 9.12.5.2, “DNS Lookup Optimization and the Host Cache”.

    Depending on the network configuration of your system and the Host values for your accounts, clients may need to connect using an explicit --host option, such as --host=127.0.0.1 or --host=::1.

    An attempt to connect to the host 127.0.0.1 normally resolves to the localhost account. However, this fails if the server is run with the --skip-name-resolve option, so make sure that an account exists that can accept a connection. For example, to be able to connect as root using --host=127.0.0.1 or --host=::1, create these accounts:

    CREATE USER 'root'@'127.0.0.1' IDENTIFIED BY 'root-password';
    CREATE USER 'root'@'::1' IDENTIFIED BY 'root-password';
    
  • --skip-networking

    Do not listen for TCP/IP connections at all. All interaction with mysqld must be made using named pipes or shared memory (on Windows) or Unix socket files (on Unix). This option is highly recommended for systems where only local clients are permitted. See Section 9.12.5.2, “DNS Lookup Optimization and the Host Cache”.

  • --skip-partition

    Deprecated5.7.16
    Command-Line Format--skip-partition
     --disable-partition

    Disables user-defined partitioning. Partitioned tables can be seen using SHOW TABLES or by querying the INFORMATION_SCHEMA.TABLES table, but cannot be created or modified, nor can data in such tables be accessed. All partition-specific columns in the INFORMATION_SCHEMA.PARTITIONS table display NULL.

    Since DROP TABLE removes table definition (.frm) files, this statement works on partitioned tables even when partitioning is disabled using the option. The statement, however, does not remove partition definitions associated with partitioned tables in such cases. For this reason, you should avoid dropping partitioned tables with partitioning disabled, or take action to remove orphaned .par files manually (if present).

    Note

    As of MySQL 5.7.6, partition definition (.par) files are no longer created. Instead, partition definitions are stored in the internal data dictionary.

    This option is deprecated in MySQL 5.7.16, and is removed from MySQL 8.0.

  • --ssl*

    Options that begin with --ssl specify whether to permit clients to connect using SSL and indicate where to find SSL keys and certificates. See Section 7.4.5, “Command Options for Secure Connections”.

  • --standalone

    Command-Line Format--standalone
    Platform SpecificWindows

    Available on Windows only; instructs the MySQL server not to run as a service.

  • --super-large-pages

    Command-Line Format--super-large-pages
    Platform SpecificSolaris
    Permitted Values (Solaris)Typeboolean
    DefaultFALSE

    Standard use of large pages in MySQL attempts to use the largest size supported, up to 4MB. Under Solaris, a super large pages feature enables uses of pages up to 256MB. This feature is available for recent SPARC platforms. It can be enabled or disabled by using the --super-large-pages or --skip-super-large-pages option.

  • --symbolic-links, --skip-symbolic-links

    Command-Line Format--symbolic-links

    Enable or disable symbolic link support. On Unix, enabling symbolic links means that you can link a MyISAM index file or data file to another directory with the INDEX DIRECTORY or DATA DIRECTORY options of the CREATE TABLE statement. If you delete or rename the table, the files that its symbolic links point to also are deleted or renamed. See Section 9.12.3.2, “Using Symbolic Links for MyISAM Tables on Unix”.

    This option has no meaning on Windows.

  • --skip-show-database

    Command-Line Format--skip-show-database
    System VariableNameskip_show_database
    Variable ScopeGlobal
    Dynamic VariableNo

    This option sets the skip_show_database system variable that controls who is permitted to use the SHOW DATABASES statement. See Section 6.1.5, “Server System Variables”.

  • --skip-stack-trace

    Command-Line Format--skip-stack-trace

    Do not write stack traces. This option is useful when you are running mysqld under a debugger. On some systems, you also must use this option to get a core file. See Section 28.5, “Debugging and Porting MySQL”.

  • --slow-query-log[={0|1}]

    Command-Line Format--slow-query-log
    System VariableNameslow_query_log
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Specify the initial slow query log state. With no argument or an argument of 1, the --slow-query-log option enables the log. If omitted or given with an argument of 0, the option disables the log.

  • --slow-start-timeout=timeout

    Command-Line Format--slow-start-timeout=#
    Permitted Values (Windows)Typeinteger
    Default15000

    This option controls the Windows service control manager's service start timeout. The value is the maximum number of milliseconds that the service control manager waits before trying to kill the windows service during startup. The default value is 15000 (15 seconds). If the MySQL service takes too long to start, you may need to increase this value. A value of 0 means there is no timeout.

  • --socket=path

    Command-Line Format--socket={file_name|pipe_name}
    System VariableNamesocket
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring
    Default/tmp/mysql.sock

    On Unix, this option specifies the Unix socket file to use when listening for local connections. The default value is /tmp/mysql.sock. If this option is given, the server creates the file in the data directory unless an absolute path name is given to specify a different directory. On Windows, the option specifies the pipe name to use when listening for local connections that use a named pipe. The default value is MySQL (not case sensitive).

  • --sql-mode=value[,value[,value...]]

    Command-Line Format--sql-mode=name
    System VariableNamesql_mode
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (<= 5.7.4)Typeset
    DefaultNO_ENGINE_SUBSTITUTION
    Valid ValuesALLOW_INVALID_DATES
    ANSI_QUOTES
    ERROR_FOR_DIVISION_BY_ZERO
    HIGH_NOT_PRECEDENCE
    IGNORE_SPACE
    NO_AUTO_CREATE_USER
    NO_AUTO_VALUE_ON_ZERO
    NO_BACKSLASH_ESCAPES
    NO_DIR_IN_CREATE
    NO_ENGINE_SUBSTITUTION
    NO_FIELD_OPTIONS
    NO_KEY_OPTIONS
    NO_TABLE_OPTIONS
    NO_UNSIGNED_SUBTRACTION
    NO_ZERO_DATE
    NO_ZERO_IN_DATE
    ONLY_FULL_GROUP_BY
    PAD_CHAR_TO_FULL_LENGTH
    PIPES_AS_CONCAT
    REAL_AS_FLOAT
    STRICT_ALL_TABLES
    STRICT_TRANS_TABLES
    Permitted Values (>= 5.7.5, <= 5.7.6)Typeset
    DefaultONLY_FULL_GROUP_BY STRICT_TRANS_TABLES NO_ENGINE_SUBSTITUTION
    Valid ValuesALLOW_INVALID_DATES
    ANSI_QUOTES
    ERROR_FOR_DIVISION_BY_ZERO
    HIGH_NOT_PRECEDENCE
    IGNORE_SPACE
    NO_AUTO_CREATE_USER
    NO_AUTO_VALUE_ON_ZERO
    NO_BACKSLASH_ESCAPES
    NO_DIR_IN_CREATE
    NO_ENGINE_SUBSTITUTION
    NO_FIELD_OPTIONS
    NO_KEY_OPTIONS
    NO_TABLE_OPTIONS
    NO_UNSIGNED_SUBTRACTION
    NO_ZERO_DATE
    NO_ZERO_IN_DATE
    ONLY_FULL_GROUP_BY
    PAD_CHAR_TO_FULL_LENGTH
    PIPES_AS_CONCAT
    REAL_AS_FLOAT
    STRICT_ALL_TABLES
    STRICT_TRANS_TABLES
    Permitted Values (5.7.7)Typeset
    DefaultONLY_FULL_GROUP_BY STRICT_TRANS_TABLES NO_AUTO_CREATE_USER NO_ENGINE_SUBSTITUTION
    Valid ValuesALLOW_INVALID_DATES
    ANSI_QUOTES
    ERROR_FOR_DIVISION_BY_ZERO
    HIGH_NOT_PRECEDENCE
    IGNORE_SPACE
    NO_AUTO_CREATE_USER
    NO_AUTO_VALUE_ON_ZERO
    NO_BACKSLASH_ESCAPES
    NO_DIR_IN_CREATE
    NO_ENGINE_SUBSTITUTION
    NO_FIELD_OPTIONS
    NO_KEY_OPTIONS
    NO_TABLE_OPTIONS
    NO_UNSIGNED_SUBTRACTION
    NO_ZERO_DATE
    NO_ZERO_IN_DATE
    ONLY_FULL_GROUP_BY
    PAD_CHAR_TO_FULL_LENGTH
    PIPES_AS_CONCAT
    REAL_AS_FLOAT
    STRICT_ALL_TABLES
    STRICT_TRANS_TABLES
    Permitted Values (>= 5.7.8)Typeset
    DefaultONLY_FULL_GROUP_BY STRICT_TRANS_TABLES NO_ZERO_IN_DATE NO_ZERO_DATE ERROR_FOR_DIVISION_BY_ZERO NO_AUTO_CREATE_USER NO_ENGINE_SUBSTITUTION
    Valid ValuesALLOW_INVALID_DATES
    ANSI_QUOTES
    ERROR_FOR_DIVISION_BY_ZERO
    HIGH_NOT_PRECEDENCE
    IGNORE_SPACE
    NO_AUTO_CREATE_USER
    NO_AUTO_VALUE_ON_ZERO
    NO_BACKSLASH_ESCAPES
    NO_DIR_IN_CREATE
    NO_ENGINE_SUBSTITUTION
    NO_FIELD_OPTIONS
    NO_KEY_OPTIONS
    NO_TABLE_OPTIONS
    NO_UNSIGNED_SUBTRACTION
    NO_ZERO_DATE
    NO_ZERO_IN_DATE
    ONLY_FULL_GROUP_BY
    PAD_CHAR_TO_FULL_LENGTH
    PIPES_AS_CONCAT
    REAL_AS_FLOAT
    STRICT_ALL_TABLES
    STRICT_TRANS_TABLES

    Set the SQL mode. See Section 6.1.8, “Server SQL Modes”.

    Note

    MySQL installation programs may configure the SQL mode during the installation process. For example, mysql_install_db creates a default option file named my.cnf in the base installation directory. This file contains a line that sets the SQL mode; see Section 5.4.2, “mysql_install_db — Initialize MySQL Data Directory”.

    If the SQL mode differs from the default or from what you expect, check for a setting in an option file that the server reads at startup.

  • --sysdate-is-now

    Command-Line Format--sysdate-is-now
    Permitted ValuesTypeboolean
    DefaultFALSE

    SYSDATE() by default returns the time at which it executes, not the time at which the statement in which it occurs begins executing. This differs from the behavior of NOW(). This option causes SYSDATE() to be an alias for NOW(). For information about the implications for binary logging and replication, see the description for SYSDATE() in Section 13.7, “Date and Time Functions” and for SET TIMESTAMP in Section 6.1.5, “Server System Variables”.

  • --tc-heuristic-recover={COMMIT|ROLLBACK}

    Command-Line Format--tc-heuristic-recover=name
    Permitted ValuesTypeenumeration
    DefaultCOMMIT
    Valid ValuesCOMMIT
    ROLLBACK

    The type of decision to use in the heuristic recovery process. To use this option, two or more storage engines that support XA transactions must be installed.

    Prior to MySQL 5.7.8, the server interprets --tc-heuristic-recover option values incorrectly due to an off-by-one error (Bug #70860).

  • --temp-pool

    Deprecated5.7.18
    Command-Line Format--temp-pool
    Permitted ValuesTypeboolean
    DefaultTRUE

    This option causes most temporary files created by the server to use a small set of names, rather than a unique name for each new file. This works around a problem in the Linux kernel dealing with creating many new files with different names. With the old behavior, Linux seems to leak memory, because it is being allocated to the directory entry cache rather than to the disk cache. This option is ignored except on Linux.

    As of MySQL 5.7.18, this option is deprecated and is MySQL 8.0.

  • --transaction-isolation=level

    Command-Line Format--transaction-isolation=name
    Permitted ValuesTypeenumeration
    DefaultREPEATABLE-READ
    Valid ValuesREAD-UNCOMMITTED
    READ-COMMITTED
    REPEATABLE-READ
    SERIALIZABLE

    Sets the default transaction isolation level. The level value can be READ-UNCOMMITTED, READ-COMMITTED, REPEATABLE-READ, or SERIALIZABLE. See Section 14.3.6, “SET TRANSACTION Syntax”.

    The default transaction isolation level can also be set at runtime using the SET TRANSACTION statement or by setting the tx_isolation system variable.

  • --transaction-read-only

    Command-Line Format--transaction-read-only
    Permitted ValuesTypeboolean
    DefaultOFF

    Sets the default transaction access mode. By default, read-only mode is disabled, so the mode is read/write.

    To set the default transaction access mode at runtime, use the SET TRANSACTION statement or set the tx_read_only system variable. See Section 14.3.6, “SET TRANSACTION Syntax”.

  • --tmpdir=dir_name, -t dir_name

    Command-Line Format--tmpdir=dir_name
    System VariableNametmpdir
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name

    The path of the directory to use for creating temporary files. It might be useful if your default /tmp directory resides on a partition that is too small to hold temporary tables. This option accepts several paths that are used in round-robin fashion. Paths should be separated by colon characters (:) on Unix and semicolon characters (;) on Windows. If the MySQL server is acting as a replication slave, you should not set --tmpdir to point to a directory on a memory-based file system or to a directory that is cleared when the server host restarts. For more information about the storage location of temporary files, see Section B.5.3.5, “Where MySQL Stores Temporary Files”. A replication slave needs some of its temporary files to survive a machine restart so that it can replicate temporary tables or LOAD DATA INFILE operations. If files in the temporary file directory are lost when the server restarts, replication fails.

  • --user={user_name|user_id}, -u {user_name|user_id}

    Command-Line Format--user=name
    Permitted ValuesTypestring

    Run the mysqld server as the user having the name user_name or the numeric user ID user_id. (User in this context refers to a system login account, not a MySQL user listed in the grant tables.)

    This option is mandatory when starting mysqld as root. The server changes its user ID during its startup sequence, causing it to run as that particular user rather than as root. See Section 7.1.1, “Security Guidelines”.

    To avoid a possible security hole where a user adds a --user=root option to a my.cnf file (thus causing the server to run as root), mysqld uses only the first --user option specified and produces a warning if there are multiple --user options. Options in /etc/my.cnf and $MYSQL_HOME/my.cnf are processed before command-line options, so it is recommended that you put a --user option in /etc/my.cnf and specify a value other than root. The option in /etc/my.cnf is found before any other --user options, which ensures that the server runs as a user other than root, and that a warning results if any other --user option is found.

  • --verbose, -v

    Use this option with the --help option for detailed help.

  • --version, -V

    Display version information and exit.

6.1.5 Server System Variables

The MySQL server maintains many system variables that indicate how it is configured. Each system variable has a default value. System variables can be set at server startup using options on the command line or in an option file. Most of them can be changed dynamically at runtime using the SET statement, which enables you to modify operation of the server without having to stop and restart it. Setting the global value of a system variable requires the SUPER privilege. For some system variables, setting the session value also requires the SUPER privilege; if so, it is indicated in the variable description. You can also use system variable values in expressions.

There are several ways to see the names and values of system variables:

  • To see the values that a server will use based on its compiled-in defaults and any option files that it reads, use this command:

    mysqld --verbose --help
    
  • To see the values that a server will use based on its compiled-in defaults, ignoring the settings in any option files, use this command:

    mysqld --no-defaults --verbose --help
    
  • To see the current values used by a running server, use the SHOW VARIABLES statement or the Performance Schema system variable tables. See Section 25.10.13, “Performance Schema System Variable Tables”.

This section includes a table that lists all system variables and following the table provides a description of each one. Variables with no version indicated are present in all MySQL 5.7 releases. For more information about manipulation of system variables, see Section 6.1.6, “Using System Variables”.

Table 6.2 System Variable Summary

NameCmd-LineOption FileSystem VarVar ScopeDynamic
audit_log_buffer_sizeYesYesYesGlobalNo
audit_log_connection_policyYesYesYesGlobalYes
audit_log_current_session  YesBothNo
audit_log_exclude_accountsYesYesYesGlobalYes
audit_log_fileYesYesYesGlobalNo
audit_log_filter_id  YesBothNo
audit_log_flush  YesGlobalYes
audit_log_formatYesYesYesGlobalNo
audit_log_include_accountsYesYesYesGlobalYes
audit_log_policyYesYesYesGlobalNo
audit_log_rotate_on_sizeYesYesYesGlobalYes
audit_log_statement_policyYesYesYesGlobalYes
audit_log_strategyYesYesYesGlobalNo
auto_generate_certsYesYesYesGlobalNo
auto_increment_increment  YesBothYes
auto_increment_offset  YesBothYes
autocommitYesYesYesBothYes
automatic_sp_privileges  YesGlobalYes
avoid_temporal_upgradeYesYesYesGlobalYes
back_log  YesGlobalNo
basedirYesYesYesGlobalNo
big-tablesYesYes  Yes
- Variable: big_tables  YesBothYes
bind-addressYesYes  No
- Variable: bind_address  YesGlobalNo
binlog_cache_sizeYesYesYesGlobalYes
binlog_checksum  YesGlobalYes
binlog_direct_non_transactional_updatesYesYesYesBothYes
binlog_error_actionYesYesYesBothYes
binlog-formatYesYes  Yes
- Variable: binlog_format  YesBothYes
binlog_group_commit_sync_delayYesYesYesGlobalYes
binlog_group_commit_sync_no_delay_countYesYesYesGlobalYes
binlog_gtid_simple_recoveryYesYesYesGlobalNo
binlog_max_flush_queue_time  YesGlobalYes
binlog_order_commits  YesGlobalYes
binlog_row_imageYesYesYesBothYes
binlog_rows_query_log_events  YesBothYes
binlog_stmt_cache_sizeYesYesYesGlobalYes
binlogging_impossible_modeYesYesYesBothYes
block_encryption_modeYesYesYesBothYes
bulk_insert_buffer_sizeYesYesYesBothYes
character_set_client  YesBothYes
character_set_connection  YesBothYes
character_set_database[a]  YesBothYes
character-set-filesystemYesYes  Yes
- Variable: character_set_filesystem  YesBothYes
character_set_results  YesBothYes
character-set-serverYesYes  Yes
- Variable: character_set_server  YesBothYes
character_set_system  YesGlobalNo
character-sets-dirYesYes  No
- Variable: character_sets_dir  YesGlobalNo
check_proxy_usersYesYesYesGlobalYes
collation_connection  YesBothYes
collation_database[b]  YesBothYes
collation-serverYesYes  Yes
- Variable: collation_server  YesBothYes
completion_typeYesYesYesBothYes
concurrent_insertYesYesYesGlobalYes
connect_timeoutYesYesYesGlobalYes
connection_control_failed_connections_thresholdYesYesYesGlobalYes
connection_control_max_connection_delayYesYesYesGlobalYes
connection_control_min_connection_delayYesYesYesGlobalYes
core_file  YesGlobalNo
daemon_memcached_enable_binlogYesYesYesGlobalNo
daemon_memcached_engine_lib_nameYesYesYesGlobalNo
daemon_memcached_engine_lib_pathYesYesYesGlobalNo
daemon_memcached_optionYesYesYesGlobalNo
daemon_memcached_r_batch_sizeYesYesYesGlobalNo
daemon_memcached_w_batch_sizeYesYesYesGlobalNo
datadirYesYesYesGlobalNo
date_format  YesGlobalNo
datetime_format  YesGlobalNo
debugYesYesYesBothYes
debug_sync  YesSessionYes
default_authentication_pluginYesYesYesGlobalNo
default_password_lifetimeYesYesYesGlobalYes
default-storage-engineYesYes  Yes
- Variable: default_storage_engine  YesBothYes
default_tmp_storage_engineYesYesYesBothYes
default_week_formatYesYesYesBothYes
delay-key-writeYesYes  Yes
- Variable: delay_key_write  YesGlobalYes
delayed_insert_limitYesYesYesGlobalYes
delayed_insert_timeoutYesYesYesGlobalYes
delayed_queue_sizeYesYesYesGlobalYes
disabled_storage_enginesYesYesYesGlobalNo
disconnect_on_expired_passwordYesYesYesSessionNo
div_precision_incrementYesYesYesBothYes
end_markers_in_json  YesBothYes
enforce-gtid-consistencyYesYesYesGlobalVaries
enforce_gtid_consistencyYesYesYesGlobalVaries
eq_range_index_dive_limit  YesBothYes
error_count  YesSessionNo
event-schedulerYesYes  Yes
- Variable: event_scheduler  YesGlobalYes
executed_gtids_compression_period  YesGlobalYes
expire_logs_daysYesYesYesGlobalYes
explicit_defaults_for_timestampYesYesYesBothYes
external_user  YesSessionNo
flushYesYesYesGlobalYes
flush_timeYesYesYesGlobalYes
foreign_key_checks  YesBothYes
ft_boolean_syntaxYesYesYesGlobalYes
ft_max_word_lenYesYesYesGlobalNo
ft_min_word_lenYesYesYesGlobalNo
ft_query_expansion_limitYesYesYesGlobalNo
ft_stopword_fileYesYesYesGlobalNo
general-logYesYes  Yes
- Variable: general_log  YesGlobalYes
general_log_fileYesYesYesGlobalYes
group_concat_max_lenYesYesYesBothYes
group_replication_allow_local_disjoint_gtids_joinYesYesYesGlobalYes
group_replication_allow_local_lower_version_joinYesYesYesGlobalYes
group_replication_auto_increment_incrementYesYesYesGlobalYes
group_replication_bootstrap_groupYesYesYesGlobalYes
group_replication_components_stop_timeoutYesYesYesGlobalYes
group_replication_compression_thresholdYesYesYesGlobalYes
group_replication_enforce_update_everywhere_checksYesYesYesGlobalYes
group_replication_flow_control_applier_thresholdYesYesYesGlobalYes
group_replication_flow_control_certifier_thresholdYesYesYesGlobalYes
group_replication_flow_control_modeYesYesYesGlobalYes
group_replication_force_membersYesYesYesGlobalYes
group_replication_group_nameYesYesYesGlobalYes
group_replication_group_seedsYesYesYesGlobalYes
group_replication_gtid_assignment_block_sizeYesYesYesGlobalYes
group_replication_ip_whitelistYesYesYesGlobalYes
group_replication_local_addressYesYesYesGlobalYes
group_replication_poll_spin_loopsYesYesYesGlobalYes
group_replication_recovery_complete_atYesYesYesGlobalYes
group_replication_recovery_reconnect_intervalYesYesYesGlobalYes
group_replication_recovery_retry_countYesYesYesGlobalYes
group_replication_recovery_ssl_caYesYesYesGlobalYes
group_replication_recovery_ssl_capathYesYesYesGlobalYes
group_replication_recovery_ssl_certYesYesYesGlobalYes
group_replication_recovery_ssl_cipherYesYesYesGlobalYes
group_replication_recovery_ssl_crlYesYesYesGlobalYes
group_replication_recovery_ssl_crlpathYesYesYesGlobalYes
group_replication_recovery_ssl_keyYesYesYesGlobalYes
group_replication_recovery_ssl_verify_server_certYesYesYesGlobalYes
group_replication_recovery_use_sslYesYesYesGlobalYes
group_replication_single_primary_modeYesYesYesGlobalYes
group_replication_ssl_modeYesYesYesGlobalYes
group_replication_start_on_bootYesYesYesGlobalYes
gtid_executed  YesVariesNo
gtid_executed_compression_period  YesGlobalYes
gtid-modeYesYes  Varies
- Variable: gtid_mode  YesGlobalVaries
gtid_mode  YesGlobalVaries
gtid_next  YesSessionYes
gtid_owned  YesBothNo
gtid_purged  YesGlobalYes
have_compress  YesGlobalNo
have_crypt  YesGlobalNo
have_dynamic_loading  YesGlobalNo
have_geometry  YesGlobalNo
have_openssl  YesGlobalNo
have_profiling  YesGlobalNo
have_query_cache  YesGlobalNo
have_rtree_keys  YesGlobalNo
have_ssl  YesGlobalNo
have_statement_timeout  YesGlobalNo
have_symlink  YesGlobalNo
host_cache_size  YesGlobalYes
hostname  YesGlobalNo
identity  YesSessionYes
ignore-builtin-innodbYesYes  No
- Variable: ignore_builtin_innodb  YesGlobalNo
ignore_db_dirs  YesGlobalNo
init_connectYesYesYesGlobalYes
init-fileYesYes  No
- Variable: init_file  YesGlobalNo
init_slaveYesYesYesGlobalYes
innodb_adaptive_flushingYesYesYesGlobalYes
innodb_adaptive_flushing_lwmYesYesYesGlobalYes
innodb_adaptive_hash_indexYesYesYesGlobalYes
innodb_adaptive_hash_index_partsYesYesYesGlobalNo
innodb_adaptive_max_sleep_delayYesYesYesGlobalYes
innodb_additional_mem_pool_sizeYesYesYesGlobalNo
innodb_api_bk_commit_intervalYesYesYesGlobalYes
innodb_api_disable_rowlockYesYesYesGlobalNo
innodb_api_enable_binlogYesYesYesGlobalNo
innodb_api_enable_mdlYesYesYesGlobalNo
innodb_api_trx_levelYesYesYesGlobalYes
innodb_autoextend_incrementYesYesYesGlobalYes
innodb_autoinc_lock_modeYesYesYesGlobalNo
innodb_background_drop_list_emptyYesYesYesGlobalYes
innodb_buffer_pool_chunk_sizeYesYesYesGlobalNo
innodb_buffer_pool_dump_at_shutdownYesYesYesGlobalYes
innodb_buffer_pool_dump_nowYesYesYesGlobalYes
innodb_buffer_pool_dump_pctYesYesYesGlobalYes
innodb_buffer_pool_filenameYesYesYesGlobalYes
innodb_buffer_pool_instancesYesYesYesGlobalNo
innodb_buffer_pool_load_abortYesYesYesGlobalYes
innodb_buffer_pool_load_at_startupYesYesYesGlobalNo
innodb_buffer_pool_load_nowYesYesYesGlobalYes
innodb_buffer_pool_sizeYesYesYesGlobalVaries
innodb_change_buffer_max_sizeYesYesYesGlobalYes
innodb_change_bufferingYesYesYesGlobalYes
innodb_change_buffering_debugYesYesYesGlobalYes
innodb_checksum_algorithmYesYesYesGlobalYes
innodb_checksumsYesYesYesGlobalNo
innodb_cmp_per_index_enabledYesYesYesGlobalYes
innodb_commit_concurrencyYesYesYesGlobalYes
innodb_compress_debugYesYesYesGlobalYes
innodb_compression_failure_threshold_pctYesYesYesGlobalYes
innodb_compression_levelYesYesYesGlobalYes
innodb_compression_pad_pct_maxYesYesYesGlobalYes
innodb_concurrency_ticketsYesYesYesGlobalYes
innodb_create_intrinsicYesYesYesSessionYes
innodb_data_file_pathYesYesYesGlobalNo
innodb_data_home_dirYesYesYesGlobalNo
innodb_deadlock_detectYesYesYesGlobalYes
innodb_default_row_formatYesYesYesGlobalYes
innodb_disable_resize_buffer_pool_debugYesYesYesGlobalYes
innodb_disable_sort_file_cacheYesYesYesGlobalYes
innodb_doublewriteYesYesYesGlobalNo
innodb_fast_shutdownYesYesYesGlobalYes
innodb_fil_make_page_dirty_debugYesYesYesGlobalYes
innodb_file_formatYesYesYesGlobalYes
innodb_file_format_checkYesYesYesGlobalNo
innodb_file_format_maxYesYesYesGlobalYes
innodb_file_per_tableYesYesYesGlobalYes
innodb_fill_factorYesYesYesGlobalYes
innodb_flush_log_at_timeout  YesGlobalYes
innodb_flush_log_at_trx_commitYesYesYesGlobalYes
innodb_flush_methodYesYesYesGlobalNo
innodb_flush_neighborsYesYesYesGlobalYes
innodb_flush_syncYesYesYesGlobalYes
innodb_flushing_avg_loopsYesYesYesGlobalYes
innodb_force_load_corruptedYesYesYesGlobalNo
innodb_force_recoveryYesYesYesGlobalNo
innodb_ft_aux_tableYesYesYesGlobalYes
innodb_ft_cache_sizeYesYesYesGlobalNo
innodb_ft_enable_diag_printYesYesYesGlobalYes
innodb_ft_enable_stopwordYesYesYesGlobalYes
innodb_ft_max_token_sizeYesYesYesGlobalNo
innodb_ft_min_token_sizeYesYesYesGlobalNo
innodb_ft_num_word_optimizeYesYesYesGlobalYes
innodb_ft_result_cache_limitYesYesYesGlobalYes
innodb_ft_server_stopword_tableYesYesYesGlobalYes
innodb_ft_sort_pll_degreeYesYesYesGlobalNo
innodb_ft_total_cache_sizeYesYesYesGlobalNo
innodb_ft_user_stopword_tableYesYesYesBothYes
innodb_io_capacityYesYesYesGlobalYes
innodb_io_capacity_maxYesYesYesGlobalYes
innodb_large_prefixYesYesYesGlobalYes
innodb_limit_optimistic_insert_debugYesYesYesGlobalYes
innodb_lock_wait_timeoutYesYesYesBothYes
innodb_locks_unsafe_for_binlogYesYesYesGlobalNo
innodb_log_buffer_sizeYesYesYesGlobalNo
innodb_log_checksum_algorithmYesYesYesGlobalYes
innodb_log_checksumsYesYesYesGlobalYes
innodb_log_compressed_pagesYesYesYesGlobalYes
innodb_log_file_sizeYesYesYesGlobalNo
innodb_log_files_in_groupYesYesYesGlobalNo
innodb_log_group_home_dirYesYesYesGlobalNo
innodb_log_write_ahead_sizeYesYesYesGlobalYes
innodb_lru_scan_depthYesYesYesGlobalYes
innodb_max_dirty_pages_pctYesYesYesGlobalYes
innodb_max_dirty_pages_pct_lwmYesYesYesGlobalYes
innodb_max_purge_lagYesYesYesGlobalYes
innodb_max_purge_lag_delayYesYesYesGlobalYes
innodb_max_undo_log_sizeYesYesYesGlobalYes
innodb_merge_threshold_set_all_debugYesYesYesGlobalYes
innodb_monitor_disableYesYesYesGlobalYes
innodb_monitor_enableYesYesYesGlobalYes
innodb_monitor_resetYesYesYesGlobalYes
innodb_monitor_reset_allYesYesYesGlobalYes
innodb_numa_interleaveYesYesYesGlobalNo
innodb_old_blocks_pctYesYesYesGlobalYes
innodb_old_blocks_timeYesYesYesGlobalYes
innodb_online_alter_log_max_sizeYesYesYesGlobalYes
innodb_open_filesYesYesYesGlobalNo
innodb_optimize_fulltext_onlyYesYesYesGlobalYes
innodb_optimize_point_storageYesYesYesSessionYes
innodb_page_cleanersYesYesYesGlobalNo
innodb_page_sizeYesYesYesGlobalNo
innodb_print_all_deadlocksYesYesYesGlobalYes
innodb_purge_batch_sizeYesYesYesGlobalYes
innodb_purge_rseg_truncate_frequencyYesYesYesGlobalYes
innodb_purge_threadsYesYesYesGlobalNo
innodb_random_read_aheadYesYesYesGlobalYes
innodb_read_ahead_thresholdYesYesYesGlobalYes
innodb_read_io_threadsYesYesYesGlobalNo
innodb_read_onlyYesYesYesGlobalNo
innodb_replication_delayYesYesYesGlobalYes
innodb_rollback_on_timeoutYesYesYesGlobalNo
innodb_rollback_segmentsYesYesYesGlobalYes
innodb_saved_page_number_debugYesYesYesGlobalYes
innodb_sort_buffer_sizeYesYesYesGlobalNo
innodb_spin_wait_delayYesYesYesGlobalYes
innodb_stats_auto_recalcYesYesYesGlobalYes
innodb_stats_include_delete_markedYesYesYesGlobalYes
innodb_stats_methodYesYesYesGlobalYes
innodb_stats_on_metadataYesYesYesGlobalYes
innodb_stats_persistentYesYesYesGlobalYes
innodb_stats_persistent_sample_pagesYesYesYesGlobalYes
innodb_stats_sample_pagesYesYesYesGlobalYes
innodb_stats_transient_sample_pagesYesYesYesGlobalYes
innodb_status_outputYesYesYesGlobalYes
innodb_status_output_locksYesYesYesGlobalYes
innodb_strict_modeYesYesYesBothYes
innodb_support_xaYesYesYesBothYes
innodb_sync_array_sizeYesYesYesGlobalNo
innodb_sync_debugYesYesYesGlobalNo
innodb_sync_spin_loopsYesYesYesGlobalYes
innodb_table_locksYesYesYesBothYes
innodb_temp_data_file_pathYesYesYesGlobalNo
innodb_thread_concurrencyYesYesYesGlobalYes
innodb_thread_sleep_delayYesYesYesGlobalYes
innodb_tmpdirYesYesYesBothYes
innodb_trx_purge_view_update_only_debugYesYesYesGlobalYes
innodb_trx_rseg_n_slots_debugYesYesYesGlobalYes
innodb_undo_directoryYesYesYesGlobalNo
innodb_undo_log_truncateYesYesYesGlobalYes
innodb_undo_logsYesYesYesGlobalYes
innodb_undo_tablespacesYesYesYesGlobalNo
innodb_use_native_aioYesYesYesGlobalNo
innodb_use_sys_mallocYesYesYesGlobalNo
innodb_version  YesGlobalNo
innodb_write_io_threadsYesYesYesGlobalNo
insert_id  YesSessionYes
interactive_timeoutYesYesYesBothYes
internal_tmp_disk_storage_engineYesYesYesGlobalYes
join_buffer_sizeYesYesYesBothYes
keep_files_on_createYesYesYesBothYes
key_buffer_sizeYesYesYesGlobalYes
key_cache_age_thresholdYesYesYesGlobalYes
key_cache_block_sizeYesYesYesGlobalYes
key_cache_division_limitYesYesYesGlobalYes
keyring_file_dataYesYesYesGlobalYes
keyring_okv_conf_dirYesYesYesGlobalYes
languageYesYesYesGlobalNo
large_files_support  YesGlobalNo
large_page_size  YesGlobalNo
large-pagesYesYes  No
- Variable: large_pages  YesGlobalNo
last_insert_id  YesSessionYes
lc-messagesYesYes  Yes
- Variable: lc_messages  YesBothYes
lc-messages-dirYesYes  No
- Variable: lc_messages_dir  YesGlobalNo
lc_time_names  YesBothYes
license  YesGlobalNo
local_infile  YesGlobalYes
lock_wait_timeoutYesYesYesBothYes
locked_in_memory  YesGlobalNo
log_backward_compatible_user_definitionsYesYesYesGlobalYes
log-binYesYesYesGlobalNo
log_bin  YesGlobalNo
log_bin_basename  YesGlobalNo
log_bin_index  YesGlobalNo
log-bin-trust-function-creatorsYesYes  Yes
- Variable: log_bin_trust_function_creators  YesGlobalYes
log-bin-use-v1-row-eventsYesYes  No
- Variable: log_bin_use_v1_row_events  YesGlobalNo
log_bin_use_v1_row_eventsYesYesYesGlobalNo
log_builtin_as_identified_by_passwordYesYesYesGlobalYes
log-errorYesYes  No
- Variable: log_error  YesGlobalNo
log_error_verbosityYesYesYesGlobalYes
log-outputYesYes  Yes
- Variable: log_output  YesGlobalYes
log-queries-not-using-indexesYesYes  Yes
- Variable: log_queries_not_using_indexes  YesGlobalYes
log-slave-updatesYesYes  No
- Variable: log_slave_updates  YesGlobalNo
log_slave_updatesYesYesYesGlobalNo
log_slow_admin_statements  YesGlobalYes
log_slow_slave_statements  YesGlobalYes
log_statements_unsafe_for_binlog  YesGlobalYes
log_syslogYesYesYesGlobalYes
log_syslog_facilityYesYesYesGlobalYes
log_syslog_include_pidYesYesYesGlobalYes
log_syslog_tagYesYesYesGlobalYes
log_throttle_queries_not_using_indexes  YesGlobalYes
log_timestampsYesYesYesGlobalYes
log-warningsYesYes  Yes
- Variable: log_warnings  YesGlobalYes
long_query_timeYesYesYesBothYes
low-priority-updatesYesYes  Yes
- Variable: low_priority_updates  YesBothYes
lower_case_file_system  YesGlobalNo
lower_case_table_namesYesYesYesGlobalNo
master_info_repositoryYesYesYesGlobalYes
master_verify_checksum  YesGlobalYes
max_allowed_packetYesYesYesBothYes
max_binlog_cache_sizeYesYesYesGlobalYes
max_binlog_sizeYesYesYesGlobalYes
max_binlog_stmt_cache_sizeYesYesYesGlobalYes
max_connect_errorsYesYesYesGlobalYes
max_connectionsYesYesYesGlobalYes
max_delayed_threadsYesYesYesBothYes
max_digest_lengthYesYesYesGlobalNo
max_error_countYesYesYesBothYes
max_execution_timeYesYesYesBothYes
max_heap_table_sizeYesYesYesBothYes
max_insert_delayed_threads  YesBothYes
max_join_sizeYesYesYesBothYes
max_length_for_sort_dataYesYesYesBothYes
max_points_in_geometryYesYesYesGlobalYes
max_prepared_stmt_countYesYesYesGlobalYes
max_relay_log_sizeYesYesYesGlobalYes
max_seeks_for_keyYesYesYesBothYes
max_sort_lengthYesYesYesBothYes
max_sp_recursion_depthYesYesYesBothYes
max_statement_time  YesBothYes
max_tmp_tables  YesBothYes
max_user_connectionsYesYesYesBothYes
max_write_lock_countYesYesYesGlobalYes
mecab_rc_fileYesYesYesGlobalNo
metadata_locks_cache_size  YesGlobalNo
metadata_locks_hash_instances  YesGlobalNo
min-examined-row-limitYesYesYesBothYes
multi_range_countYesYesYesBothYes
myisam_data_pointer_sizeYesYesYesGlobalYes
myisam_max_sort_file_sizeYesYesYesGlobalYes
myisam_mmap_sizeYesYesYesGlobalNo
myisam_recover_options  YesGlobalNo
myisam_repair_threadsYesYesYesBothYes
myisam_sort_buffer_sizeYesYesYesBothYes
myisam_stats_methodYesYesYesBothYes
myisam_use_mmapYesYesYesGlobalYes
mysql_firewall_modeYesYesYesGlobalYes
mysql_firewall_traceYesYesYesGlobalYes
mysql_native_password_proxy_usersYesYesYesGlobalYes
mysqlx_bind_addressYesYesYesGlobalNo
mysqlx_connect_timeoutYesYesYesGlobalYes
mysqlx_max_connectionsYesYesYesGlobalYes
mysqlx_portYesYesYesGlobalNo
mysqlx_port_open_timeoutYesYesYesGlobalNo
mysqlx-socketYesYesYesGlobalNo
mysqlx_socket  YesGlobalNo
mysqlx_sslYesYesYesGlobalNo
mysqlx_ssl_caYesYesYesGlobalNo
mysqlx_ssl_capathYesYesYesGlobalNo
mysqlx_ssl_certYesYesYesGlobalNo
mysqlx_ssl_crlYesYesYesGlobalNo
mysqlx_ssl_crlpathYesYesYesGlobalNo
mysqlx_ssl_keyYesYesYesGlobalNo
named_pipe  YesGlobalNo
ndb-allow-copying-alter-tableYesYesYesBothYes
ndb_autoincrement_prefetch_szYesYesYesBothYes
ndb-batch-sizeYesYesYesGlobalNo
ndb-blob-read-batch-bytesYesYesYesBothYes
ndb-blob-write-batch-bytesYesYesYesBothYes
ndb_cache_check_timeYesYesYesGlobalYes
ndb_clear_apply_statusYes YesGlobalYes
ndb-cluster-connection-poolYesYesYesGlobalNo
ndb-cluster-connection-pool-nodeidsYesYesYesGlobalNo
ndb_data_node_neighbourYesYesYesGlobalYes
ndb-default-column-formatYesYes  Yes
- Variable: ndb_default_column_format  YesGlobalYes
ndb_default_column_formatYesYesYesGlobalYes
ndb-deferred-constraintsYesYes  Yes
- Variable: ndb_deferred_constraints  YesBothYes
ndb_deferred_constraintsYesYesYesBothYes
ndb-distributionYesYes  Yes
- Variable: ndb_distribution  YesGlobalYes
ndb_distributionYesYesYesGlobalYes
ndb_eventbuffer_free_percentYesYesYesGlobalYes
ndb_eventbuffer_max_allocYesYesYesGlobalYes
ndb_extra_loggingYesYesYesGlobalYes
ndb_force_sendYesYesYesBothYes
ndb_fully_replicatedYesYesYesBothYes
ndb_index_stat_enableYesYesYesBothYes
ndb_index_stat_optionYesYesYesBothYes
ndb_join_pushdown  YesBothYes
ndb-log-apply-statusYesYes  No
- Variable: ndb_log_apply_status  YesGlobalNo
ndb_log_apply_statusYesYesYesGlobalNo
ndb_log_binYes YesBothYes
ndb_log_binlog_indexYes YesGlobalYes
ndb-log-empty-epochsYesYesYesGlobalYes
ndb_log_empty_epochsYesYesYesGlobalYes
ndb-log-empty-updateYesYesYesGlobalYes
ndb_log_empty_updateYesYesYesGlobalYes
ndb-log-exclusive-readsYesYes  Yes
- Variable: ndb_log_exclusive_reads  YesBothYes
ndb_log_exclusive_readsYesYesYesBothYes
ndb-log-origYesYes  No
- Variable: ndb_log_orig  YesGlobalNo
ndb_log_origYesYesYesGlobalNo
ndb-log-transaction-idYesYes  No
- Variable: ndb_log_transaction_id  YesGlobalNo
ndb_log_transaction_id  YesGlobalNo
ndb_log_updated_onlyYesYesYesGlobalYes
ndb_optimization_delay  YesGlobalYes
ndb_optimized_node_selectionYesYesYesGlobalNo
ndb_read_backupYesYesYesGlobalYes
ndb_recv_thread_cpu_mask  YesGlobalYes
ndb_report_thresh_binlog_epoch_slipYesYesYesGlobalYes
ndb_report_thresh_binlog_mem_usageYesYesYesGlobalYes
ndb_show_foreign_key_mock_tablesYesYesYesGlobalYes
ndb_slave_conflict_roleYesYesYesGlobalYes
Ndb_slave_max_replicated_epoch  YesGlobalNo
ndb_table_no_logging  YesSessionYes
ndb_table_temporary  YesSessionYes
ndb_use_copying_alter_table  YesBothNo
ndb_use_exact_count  YesBothYes
ndb_use_transactionsYesYesYesBothYes
ndb_version  YesGlobalNo
ndb_version_string  YesGlobalNo
ndb-wait-connectedYesYesYesGlobalNo
ndb-wait-setupYesYesYesGlobalNo
ndbinfo_database  YesGlobalNo
ndbinfo_max_bytesYes YesBothYes
ndbinfo_max_rowsYes YesBothYes
ndbinfo_offline  YesGlobalYes
ndbinfo_show_hiddenYes YesBothYes
ndbinfo_table_prefixYes YesBothYes
ndbinfo_version  YesGlobalNo
net_buffer_lengthYesYesYesBothYes
net_read_timeoutYesYesYesBothYes
net_retry_countYesYesYesBothYes
net_write_timeoutYesYesYesBothYes
newYesYesYesBothYes
ngram_token_sizeYesYesYesGlobalNo
offline_modeYesYesYesGlobalYes
oldYesYesYesGlobalNo
old-alter-tableYesYes  Yes
- Variable: old_alter_table  YesBothYes
old_passwords  YesBothYes
open-files-limitYesYes  No
- Variable: open_files_limit  YesGlobalNo
optimizer_prune_levelYesYesYesBothYes
optimizer_search_depthYesYesYesBothYes
optimizer_switchYesYesYesBothYes
optimizer_trace  YesBothYes
optimizer_trace_features  YesBothYes
optimizer_trace_limit  YesBothYes
optimizer_trace_max_mem_size  YesBothYes
optimizer_trace_offset  YesBothYes
parser_max_mem_sizeYesYesYesBothYes
performance_schemaYesYesYesGlobalNo
performance_schema_accounts_sizeYesYesYesGlobalNo
performance_schema_digests_sizeYesYesYesGlobalNo
performance_schema_events_stages_history_long_sizeYesYesYesGlobalNo
performance_schema_events_stages_history_sizeYesYesYesGlobalNo
performance_schema_events_statements_history_long_sizeYesYesYesGlobalNo
performance_schema_events_statements_history_sizeYesYesYesGlobalNo
performance_schema_events_transactions_history_long_sizeYesYesYesGlobalNo
performance_schema_events_transactions_history_sizeYesYesYesGlobalNo
performance_schema_events_waits_history_long_sizeYesYesYesGlobalNo
performance_schema_events_waits_history_sizeYesYesYesGlobalNo
performance_schema_hosts_sizeYesYesYesGlobalNo
performance_schema_max_cond_classesYesYesYesGlobalNo
performance_schema_max_cond_instancesYesYesYesGlobalNo
performance_schema_max_digest_lengthYesYesYesGlobalNo
performance_schema_max_file_classesYesYesYesGlobalNo
performance_schema_max_file_handlesYesYesYesGlobalNo
performance_schema_max_file_instancesYesYesYesGlobalNo
performance_schema_max_index_statYesYesYesGlobalNo
performance_schema_max_memory_classesYesYesYesGlobalNo
performance_schema_max_metadata_locksYesYesYesGlobalNo
performance_schema_max_mutex_classesYesYesYesGlobalNo
performance_schema_max_mutex_instancesYesYesYesGlobalNo
performance_schema_max_prepared_statements_instancesYesYesYesGlobalNo
performance_schema_max_program_instancesYesYesYesGlobalNo
performance_schema_max_rwlock_classesYesYesYesGlobalNo
performance_schema_max_rwlock_instancesYesYesYesGlobalNo
performance_schema_max_socket_classesYesYesYesGlobalNo
performance_schema_max_socket_instancesYesYesYesGlobalNo
performance_schema_max_sql_text_lengthYesYesYesGlobalNo
performance_schema_max_stage_classesYesYesYesGlobalNo
performance_schema_max_statement_classesYesYesYesGlobalNo
performance_schema_max_statement_stackYesYesYesGlobalNo
performance_schema_max_table_handlesYesYesYesGlobalNo
performance_schema_max_table_instancesYesYesYesGlobalNo
performance_schema_max_table_lock_statYesYesYesGlobalNo
performance_schema_max_thread_classesYesYesYesGlobalNo
performance_schema_max_thread_instancesYesYesYesGlobalNo
performance_schema_session_connect_attrs_sizeYesYesYesGlobalNo
performance_schema_setup_actors_sizeYesYesYesGlobalNo
performance_schema_setup_objects_sizeYesYesYesGlobalNo
performance_schema_users_sizeYesYesYesGlobalNo
pid-fileYesYes  No
- Variable: pid_file  YesGlobalNo
plugin_dirYesYesYesGlobalNo
portYesYesYesGlobalNo
preload_buffer_sizeYesYesYesBothYes
profiling  YesBothYes
profiling_history_sizeYesYesYesBothYes
protocol_version  YesGlobalNo
proxy_user  YesSessionNo
pseudo_slave_mode  YesSessionYes
pseudo_thread_id  YesSessionYes
query_alloc_block_sizeYesYesYesBothYes
query_cache_limitYesYesYesGlobalYes
query_cache_min_res_unitYesYesYesGlobalYes
query_cache_sizeYesYesYesGlobalYes
query_cache_typeYesYesYesBothYes
query_cache_wlock_invalidateYesYesYesBothYes
query_prealloc_sizeYesYesYesBothYes
rand_seed1  YesSessionYes
rand_seed2  YesSessionYes
range_alloc_block_sizeYesYesYesBothYes
range_optimizer_max_mem_sizeYesYesYesBothYes
rbr_exec_mode  YesSessionYes
read_buffer_sizeYesYesYesBothYes
read_onlyYesYesYesGlobalYes
read_rnd_buffer_sizeYesYesYesBothYes
relay-logYesYes  No
- Variable: relay_log  YesGlobalNo
relay_log_basename  YesGlobalNo
relay-log-indexYesYes  No
- Variable: relay_log_index  YesGlobalNo
relay_log_indexYesYesYesGlobalNo
relay_log_info_fileYesYesYesGlobalNo
relay_log_info_repository  YesGlobalYes
relay_log_purgeYesYesYesGlobalYes
relay_log_recoveryYesYesYesGlobalNo
relay_log_space_limitYesYesYesGlobalNo
report-hostYesYes  No
- Variable: report_host  YesGlobalNo
report-passwordYesYes  No
- Variable: report_password  YesGlobalNo
report-portYesYes  No
- Variable: report_port  YesGlobalNo
report-userYesYes  No
- Variable: report_user  YesGlobalNo
require_secure_transportYesYesYesGlobalYes
rewriter_enabled  YesGlobalYes
rewriter_verbose  YesGlobalYes
rpl_semi_sync_master_enabled  YesGlobalYes
rpl_semi_sync_master_timeout  YesGlobalYes
rpl_semi_sync_master_trace_level  YesGlobalYes
rpl_semi_sync_master_wait_for_slave_count  YesGlobalYes
rpl_semi_sync_master_wait_no_slave  YesGlobalYes
rpl_semi_sync_master_wait_point  YesGlobalYes
rpl_semi_sync_slave_enabled  YesGlobalYes
rpl_semi_sync_slave_trace_level  YesGlobalYes
rpl_stop_slave_timeoutYesYesYesGlobalYes
secure-authYesYes  Yes
- Variable: secure_auth  YesGlobalYes
secure-file-privYesYes  No
- Variable: secure_file_priv  YesGlobalNo
server-idYesYes  Yes
- Variable: server_id  YesGlobalYes
server-id-bitsYesYes  No
- Variable: server_id_bits  YesGlobalNo
server_id_bitsYesYesYesGlobalNo
server_uuid  YesGlobalNo
session_track_gtidsYesYesYesBothYes
session_track_schemaYesYesYesBothYes
session_track_state_changeYesYesYesBothYes
session_track_system_variablesYesYesYesBothYes
sha256_password_auto_generate_rsa_keysYesYesYesGlobalNo
sha256_password_private_key_path  YesGlobalNo
sha256_password_proxy_usersYesYesYesGlobalYes
sha256_password_public_key_path  YesGlobalNo
shared_memoryYesYesYesGlobalNo
shared_memory_base_nameYesYesYesGlobalNo
show_compatibility_56YesYesYesGlobalYes
show_old_temporalsYesYesYesBothYes
simplified_binlog_gtid_recoveryYesYesYesGlobalNo
skip_external_lockingYesYesYesGlobalNo
skip-name-resolveYesYes  No
- Variable: skip_name_resolve  YesGlobalNo
skip-networkingYesYes  No
- Variable: skip_networking  YesGlobalNo
skip-show-databaseYesYes  No
- Variable: skip_show_database  YesGlobalNo
slave_allow_batchingYesYesYesGlobalYes
slave_checkpoint_groupYesYesYesGlobalYes
slave_checkpoint_periodYesYesYesGlobalYes
slave_compressed_protocolYesYesYesGlobalYes
slave_exec_modeYesYesYesGlobalYes
slave-load-tmpdirYesYes  No
- Variable: slave_load_tmpdir  YesGlobalNo
slave_max_allowed_packet  YesGlobalYes
slave-net-timeoutYesYes  Yes
- Variable: slave_net_timeout  YesGlobalYes
slave_parallel_type  YesGlobalYes
slave_parallel_workersYes YesGlobalYes
slave_pending_jobs_size_max  YesGlobalYes
slave_preserve_commit_orderYes YesGlobalYes
slave_rows_search_algorithms  YesGlobalYes
slave-skip-errorsYesYes  No
- Variable: slave_skip_errors  YesGlobalNo
slave_sql_verify_checksum  YesGlobalYes
slave_transaction_retriesYesYesYesGlobalYes
slave_type_conversionsYesYesYesGlobalNo
slow_launch_timeYesYesYesGlobalYes
slow-query-logYesYes  Yes
- Variable: slow_query_log  YesGlobalYes
slow_query_log_fileYesYesYesGlobalYes
socketYesYesYesGlobalNo
sort_buffer_sizeYesYesYesBothYes
sql_auto_is_null  YesBothYes
sql_big_selects  YesBothYes
sql_buffer_result  YesBothYes
sql_log_bin  YesSessionYes
sql_log_off  YesBothYes
sql-modeYesYes  Yes
- Variable: sql_mode  YesBothYes
sql_notes  YesBothYes
sql_quote_show_create  YesBothYes
sql_safe_updates  YesBothYes
sql_select_limit  YesBothYes
sql_slave_skip_counter  YesGlobalYes
sql_warnings  YesBothYes
ssl-caYesYes  No
- Variable: ssl_ca  YesGlobalNo
ssl-capathYesYes  No
- Variable: ssl_capath  YesGlobalNo
ssl-certYesYes  No
- Variable: ssl_cert  YesGlobalNo
ssl-cipherYesYes  No
- Variable: ssl_cipher  YesGlobalNo
ssl-crlYesYes  No
- Variable: ssl_crl  YesGlobalNo
ssl-crlpathYesYes  No
- Variable: ssl_crlpath  YesGlobalNo
ssl-keyYesYes  No
- Variable: ssl_key  YesGlobalNo
storage_engine  YesBothYes
stored_program_cacheYesYesYesGlobalYes
super_read_onlyYesYesYesGlobalYes
sync_binlogYesYesYesGlobalYes
sync_frmYesYesYesGlobalYes
sync_master_infoYesYesYesGlobalYes
sync_relay_logYesYesYesGlobalYes
sync_relay_log_infoYesYesYesGlobalYes
system_time_zone  YesGlobalNo
table_definition_cache  YesGlobalYes
table_open_cache  YesGlobalYes
table_open_cache_instances  YesGlobalNo
thread_cache_sizeYesYesYesGlobalYes
thread_concurrencyYesYesYesGlobalNo
thread_handlingYesYesYesGlobalNo
thread_pool_algorithmYesYesYesGlobalNo
thread_pool_high_priority_connectionYesYesYesBothYes
thread_pool_max_unused_threadsYesYesYesGlobalYes
thread_pool_prio_kickup_timerYesYesYesBothYes
thread_pool_sizeYesYesYesGlobalNo
thread_pool_stall_limitYesYesYesGlobalYes
thread_stackYesYesYesGlobalNo
time_format  YesGlobalNo
time_zone  YesBothYes
timed_mutexesYesYesYesGlobalYes
timestamp  YesSessionYes
tls_versionYesYesYesGlobalNo
tmp_table_sizeYesYesYesBothYes
tmpdirYesYesYesGlobalNo
transaction_alloc_block_sizeYesYesYesBothYes
transaction_allow_batching  YesSessionYes
transaction_prealloc_sizeYesYesYesBothYes
transaction_write_set_extractionYes YesBothYes
tx_isolation  YesBothYes
tx_read_only  YesBothYes
unique_checks  YesBothYes
updatable_views_with_limitYesYesYesBothYes
validate_password_check_user_nameYesYesYesGlobalYes
validate_password_dictionary_file  YesGlobalVaries
validate_password_length  YesGlobalYes
validate_password_mixed_case_count  YesGlobalYes
validate_password_number_count  YesGlobalYes
validate_password_policy  YesGlobalYes
validate_password_special_char_count  YesGlobalYes
validate_user_plugins  YesGlobalNo
version  YesGlobalNo
version_comment  YesGlobalNo
version_compile_machine  YesGlobalNo
version_compile_os  YesGlobalNo
version_tokens_sessionYesYesYesBothYes
version_tokens_session_numberYesYesYesBothNo
wait_timeoutYesYesYesBothYes
warning_count  YesSessionNo

[a] This option is dynamic, but only the server should set this information. You should not set the value of this variable manually.

[b] This option is dynamic, but only the server should set this information. You should not set the value of this variable manually.


For additional system variable information, see these sections:

Note

Some of the following variable descriptions refer to enabling or disabling a variable. These variables can be enabled with the SET statement by setting them to ON or 1, or disabled by setting them to OFF or 0. Boolean variables can be set at startup to the values ON, TRUE, OFF, and FALSE (not case sensitive), as well as 1 and 0. See Section 5.2.5, “Program Option Modifiers”.

Some system variables control the size of buffers or caches. For a given buffer, the server might need to allocate internal data structures. These structures typically are allocated from the total memory allocated to the buffer, and the amount of space required might be platform dependent. This means that when you assign a value to a system variable that controls a buffer size, the amount of space actually available might differ from the value assigned. In some cases, the amount might be less than the value assigned. It is also possible that the server will adjust a value upward. For example, if you assign a value of 0 to a variable for which the minimal value is 1024, the server will set the value to 1024.

Values for buffer sizes, lengths, and stack sizes are given in bytes unless otherwise specified.

Some system variables take file name values. Unless otherwise specified, the default file location is the data directory if the value is a relative path name. To specify the location explicitly, use an absolute path name. Suppose that the data directory is /var/mysql/data. If a file-valued variable is given as a relative path name, it will be located under /var/mysql/data. If the value is an absolute path name, its location is as given by the path name.

  • authentication_windows_log_level

    Introduced5.7.9
    Command-Line Format--authentication_windows_log_level
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value4

    This variable is available only if the authentication_windows Windows authentication plugin is enabled and debugging code is enabled. See Section 7.5.1.6, “The Windows Native Authentication Plugin”.

    This variable sets the logging level for the Windows authentication plugin. The following table shows the permitted values.

    ValueDescription
    0No logging
    1Log only error messages
    2Log level 1 messages and warning messages
    3Log level 2 messages and information notes
    4Log level 3 messages and debug messages

    This variable was added in MySQL 5.7.9.

  • authentication_windows_use_principal_name

    Introduced5.7.9
    Command-Line Format--authentication_windows_use_principal_name
    Permitted ValuesTypeboolean
    DefaultON

    This variable is available only if the authentication_windows Windows authentication plugin is enabled. See Section 7.5.1.6, “The Windows Native Authentication Plugin”.

    A client that authenticates using the InitSecurityContext() function should provide a string identifying the service to which it connects (targetName). MySQL uses the principal name (UPN) of the account under which the server is running. The UPN has the form user_id@computer_name and need not be registered anywhere to be used. This UPN is sent by the server at the beginning of authentication handshake.

    This variable controls whether the server sends the UPN in the initial challenge. By default, the variable is enabled. For security reasons, it can be disabled to avoid sending the server's account name to a client in clear text. If the variable is disabled, the server always sends a 0x00 byte in the first challenge, the client does not specify targetName, and as a result, NTLM authentication is used.

    If the server fails to obtain its UPN (which will happen primarily in environments that do not support Kerberos authentication), the UPN is not sent by the server and NTLM authentication is used.

    This variable was added in MySQL 5.7.9.

  • autocommit

    Command-Line Format--autocommit[=#]
    System VariableNameautocommit
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultON

    The autocommit mode. If set to 1, all changes to a table take effect immediately. If set to 0, you must use COMMIT to accept a transaction or ROLLBACK to cancel it. If autocommit is 0 and you change it to 1, MySQL performs an automatic COMMIT of any open transaction. Another way to begin a transaction is to use a START TRANSACTION or BEGIN statement. See Section 14.3.1, “START TRANSACTION, COMMIT, and ROLLBACK Syntax”.

    By default, client connections begin with autocommit set to 1. To cause clients to begin with a default of 0, set the global autocommit value by starting the server with the --autocommit=0 option. To set the variable using an option file, include these lines:

    [mysqld]
    autocommit=0
    
  • automatic_sp_privileges

    System VariableNameautomatic_sp_privileges
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultTRUE

    When this variable has a value of 1 (the default), the server automatically grants the EXECUTE and ALTER ROUTINE privileges to the creator of a stored routine, if the user cannot already execute and alter or drop the routine. (The ALTER ROUTINE privilege is required to drop the routine.) The server also automatically drops those privileges from the creator when the routine is dropped. If automatic_sp_privileges is 0, the server does not automatically add or drop these privileges.

    The creator of a routine is the account used to execute the CREATE statement for it. This might not be the same as the account named as the DEFINER in the routine definition.

    See also Section 23.2.2, “Stored Routines and MySQL Privileges”.

  • auto_generate_certs

    Introduced5.7.5
    Command-Line Format--auto_generate_certs[={OFF|ON}]
    System VariableNameauto_generate_certs
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultON

    This variable is available if the server was compiled using OpenSSL (see Section 7.4.1, “OpenSSL Versus yaSSL”). It controls whether the server autogenerates SSL key and certificate files in the data directory, if they do not already exist.

    At startup, the server automatically generates server-side and client-side SSL certificate and key files in the data directory if the auto_generate_certs system variable is enabled, no SSL options other than --ssl are specified, and the server-side SSL files are missing from the data directory. These files enable secure client connections using SSL; see Section 7.4.4, “Configuring MySQL to Use Secure Connections”.

    For more information about SSL file autogeneration, including file names and characteristics, see Section 7.4.6.1, “Creating SSL and RSA Certificates and Keys using MySQL”

    The sha256_password_auto_generate_rsa_keys system variable is related but controls autogeneration of RSA key-pair files needed for secure password exchange using RSA over unencypted connections.

  • avoid_temporal_upgrade

    Introduced5.7.6
    Deprecated5.7.6
    Command-Line Format--avoid_temporal_upgrade={OFF|ON}
    System VariableNameavoid_temporal_upgrade
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    This variable controls whether ALTER TABLE implicitly upgrades temporal columns found to be in pre-5.6.4 format (TIME, DATETIME, and TIMESTAMP columns without support for fractional seconds precision). Upgrading such columns requires a table rebuild, which prevents any use of fast alterations that might otherwise apply to the operation to be performed.

    This variable is disabled by default. Enabling it causes ALTER TABLE not to rebuild temporal columns and thereby be able to take advantage of possible fast alterations.

    This variable is deprecated and will be removed in a future MySQL release.

  • back_log

    System VariableNameback_log
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default-1 (autosized)
    Min Value1
    Max Value65535

    The number of outstanding connection requests MySQL can have. This comes into play when the main MySQL thread gets very many connection requests in a very short time. It then takes some time (although very little) for the main thread to check the connection and start a new thread. The back_log value indicates how many requests can be stacked during this short time before MySQL momentarily stops answering new requests. You need to increase this only if you expect a large number of connections in a short period of time.

    In other words, this value is the size of the listen queue for incoming TCP/IP connections. Your operating system has its own limit on the size of this queue. The manual page for the Unix listen() system call should have more details. Check your OS documentation for the maximum value for this variable. back_log cannot be set higher than your operating system limit.

    The default value is based on the following formula, capped to a limit of 900:

    50 + (max_connections / 5)
    
  • basedir

    Command-Line Format--basedir=dir_name
    System VariableNamebasedir
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name

    The MySQL installation base directory. This variable can be set with the --basedir option. Relative path names for other variables usually are resolved relative to the base directory.

  • big_tables

    Command-Line Format--big-tables
    System VariableNamebig_tables
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    If set to 1, all temporary tables are stored on disk rather than in memory. This is a little slower, but the error The table tbl_name is full does not occur for SELECT operations that require a large temporary table. The default value for a new connection is 0 (use in-memory temporary tables). Normally, you should never need to set this variable, because in-memory tables are automatically converted to disk-based tables as required.

  • bind_address

    Command-Line Format--bind-address=addr
    System VariableNamebind_address
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring
    Default*

    The value of the --bind-address option.

    This variable has no effect for the embedded server (libmysqld) and as of MySQL 5.7.2 is no longer visible within the embedded server.

  • block_encryption_mode

    Introduced5.7.4
    Command-Line Format--block_encryption_mode=#
    System VariableNameblock_encryption_mode
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring
    Defaultaes-128-ecb

    This variable controls the block encryption mode for block-based algorithms such as AES. It affects encryption for AES_ENCRYPT() and AES_DECRYPT().

    block_encryption_mode takes a value in aes-keylen-mode format, where keylen is the key length in bits and mode is the encryption mode. The value is not case sensitive. Permitted keylen values are 128, 192, and 256. Permitted encryption modes depend on whether MySQL was compiled using OpenSSL or yaSSL:

    • For OpenSSL, permitted mode values are: ECB, CBC, CFB1, CFB8, CFB128, OFB

    • For yaSSL, permitted mode values are: ECB, CBC

    For example, this statement causes the AES encryption functions to use a key length of 256 bits and the CBC mode:

    SET block_encryption_mode = 'aes-256-cbc';
    

    An error occurs for attempts to set block_encryption_mode to a value containing an unsupported key length or a mode that the SSL library does not support.

  • bulk_insert_buffer_size

    Command-Line Format--bulk_insert_buffer_size=#
    System VariableNamebulk_insert_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default8388608
    Min Value0
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default8388608
    Min Value0
    Max Value18446744073709551615

    MyISAM uses a special tree-like cache to make bulk inserts faster for INSERT ... SELECT, INSERT ... VALUES (...), (...), ..., and LOAD DATA INFILE when adding data to nonempty tables. This variable limits the size of the cache tree in bytes per thread. Setting it to 0 disables this optimization. The default value is 8MB.

  • character_set_client

    System VariableNamecharacter_set_client
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring

    The character set for statements that arrive from the client. The session value of this variable is set using the character set requested by the client when the client connects to the server. (Many clients support a --default-character-set option to enable this character set to be specified explicitly. See also Section 11.1.4, “Connection Character Sets and Collations”.) The global value of the variable is used to set the session value in cases when the client-requested value is unknown or not available, or the server is configured to ignore client requests:

    • The client is from a version of MySQL older than MySQL 4.1, and thus does not request a character set.

    • The client requests a character set not known to the server. For example, a Japanese-enabled client requests sjis when connecting to a server not configured with sjis support.

    • mysqld was started with the --skip-character-set-client-handshake option, which causes it to ignore client character set configuration. This reproduces MySQL 4.0 behavior and is useful should you wish to upgrade the server without upgrading all the clients.

    ucs2, utf16, utf16le, and utf32 cannot be used as a client character set, which means that they also do not work for SET NAMES or SET CHARACTER SET.

  • character_set_connection

    System VariableNamecharacter_set_connection
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring

    The character set used for literals that do not have a character set introducer and for number-to-string conversion. For information about introducers, see Section 11.1.3.8, “Character Set Introducers”.

  • character_set_database

    System VariableNamecharacter_set_database
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    FootnoteThis option is dynamic, but only the server should set this information. You should not set the value of this variable manually.
    Permitted ValuesTypestring

    The character set used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as character_set_server.

    The global character_set_database and collation_database system variables are deprecated as of MySQL 5.7.6 and will be removed in a future version of MySQL.

    Assigning a value to the session character_set_database and collation_database system variables is deprecated as of MySQL 5.7.6 and assignments produce a warning. The session variables will become read only in a future version of MySQL and assignments will produce an error. It will remain possible to access the session variables to determine the database character set and collation for the default database.

  • character_set_filesystem

    Command-Line Format--character-set-filesystem=name
    System VariableNamecharacter_set_filesystem
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring
    Defaultbinary

    The file system character set. This variable is used to interpret string literals that refer to file names, such as in the LOAD DATA INFILE and SELECT ... INTO OUTFILE statements and the LOAD_FILE() function. Such file names are converted from character_set_client to character_set_filesystem before the file opening attempt occurs. The default value is binary, which means that no conversion occurs. For systems on which multibyte file names are permitted, a different value may be more appropriate. For example, if the system represents file names using UTF-8, set character_set_filesystem to 'utf8'.

  • character_set_results

    System VariableNamecharacter_set_results
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring

    The character set used for returning query results such as result sets or error messages to the client.

  • character_set_server

    Command-Line Format--character-set-server
    System VariableNamecharacter_set_server
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring
    Defaultlatin1

    The server's default character set.

  • character_set_system

    System VariableNamecharacter_set_system
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring
    Defaultutf8

    The character set used by the server for storing identifiers. The value is always utf8.

  • character_sets_dir

    Command-Line Format--character-sets-dir=dir_name
    System VariableNamecharacter_sets_dir
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name

    The directory where character sets are installed.

  • check_proxy_users

    Introduced5.7.7
    Command-Line Format--check_proxy_users=[={OFF|ON}]
    System VariableNamecheck_proxy_users
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    This variable controls whether the server performs proxy user mapping for authentication plugins that request it. With check_proxy_users enabled, it may also be necessary to enable plugin-specific system variables to take advantage of server proxy user mapping support:

    For information about user proxying, see Section 7.3.9, “Proxy Users”.

    This variable was added in MySQL 5.7.7. Before 5.7.7, proxy user mapping is available only for plugins that implement it for themselves.

  • collation_connection

    System VariableNamecollation_connection
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring

    The collation of the connection character set.

  • collation_database

    System VariableNamecollation_database
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    FootnoteThis option is dynamic, but only the server should set this information. You should not set the value of this variable manually.
    Permitted ValuesTypestring

    The collation used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as collation_server.

    The global character_set_database and collation_database system variables are deprecated as of MySQL 5.7.6 and will be removed in a future version of MySQL.

    Assigning a value to the session character_set_database and collation_database system variables is deprecated as of MySQL 5.7.6 and assignments produce a warning. The session variables will become read only in a future version of MySQL and assignments will produce an error. It will remain possible to access the session variables to determine the database character set and collation for the default database.

  • collation_server

    Command-Line Format--collation-server
    System VariableNamecollation_server
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring
    Defaultlatin1_swedish_ci

    The server's default collation.

  • completion_type

    Command-Line Format--completion_type=#
    System VariableNamecompletion_type
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultNO_CHAIN
    Valid ValuesNO_CHAIN
    CHAIN
    RELEASE
    0
    1
    2

    The transaction completion type. This variable can take the values shown in the following table. The variable can be assigned using either the name values or corresponding integer values.

    ValueDescription
    NO_CHAIN (or 0)COMMIT and ROLLBACK are unaffected. This is the default value.
    CHAIN (or 1)COMMIT and ROLLBACK are equivalent to COMMIT AND CHAIN and ROLLBACK AND CHAIN, respectively. (A new transaction starts immediately with the same isolation level as the just-terminated transaction.)
    RELEASE (or 2)COMMIT and ROLLBACK are equivalent to COMMIT RELEASE and ROLLBACK RELEASE, respectively. (The server disconnects after terminating the transaction.)

    completion_type affects transactions that begin with START TRANSACTION or BEGIN and end with COMMIT or ROLLBACK. It does not apply to implicit commits resulting from execution of the statements listed in Section 14.3.3, “Statements That Cause an Implicit Commit”. It also does not apply for XA COMMIT, XA ROLLBACK, or when autocommit=1.

  • concurrent_insert

    Command-Line Format--concurrent_insert[=#]
    System VariableNameconcurrent_insert
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultAUTO
    Valid ValuesNEVER
    AUTO
    ALWAYS
    0
    1
    2

    If AUTO (the default), MySQL permits INSERT and SELECT statements to run concurrently for MyISAM tables that have no free blocks in the middle of the data file. If you start mysqld with --skip-new, this variable is set to NEVER.

    This variable can take the values shown in the following table. The variable can be assigned using either the name values or corresponding integer values.

    ValueDescription
    NEVER (or 0)Disables concurrent inserts
    AUTO (or 1)(Default) Enables concurrent insert for MyISAM tables that do not have holes
    ALWAYS (or 2)Enables concurrent inserts for all MyISAM tables, even those that have holes. For a table with a hole, new rows are inserted at the end of the table if it is in use by another thread. Otherwise, MySQL acquires a normal write lock and inserts the row into the hole.

    See also Section 9.11.3, “Concurrent Inserts”.

  • connect_timeout

    Command-Line Format--connect_timeout=#
    System VariableNameconnect_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default10
    Min Value2
    Max Value31536000

    The number of seconds that the mysqld server waits for a connect packet before responding with Bad handshake. The default value is 10 seconds.

    Increasing the connect_timeout value might help if clients frequently encounter errors of the form Lost connection to MySQL server at 'XXX', system error: errno.

  • core_file

    System VariableNamecore_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultOFF

    Whether to write a core file if the server crashes. This variable is set by the --core-file option.

  • datadir

    Command-Line Format--datadir=dir_name
    System VariableNamedatadir
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name

    The MySQL data directory. This variable can be set with the --datadir option.

  • date_format

    This variable is unused. It is deprecated and will be removed in a future MySQL release.

  • datetime_format

    This variable is unused. It is deprecated and will be removed in a future MySQL release.

  • debug

    Command-Line Format--debug[=debug_options]
    System VariableNamedebug
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (Unix)Typestring
    Defaultd:t:i:o,/tmp/mysqld.trace
    Permitted Values (Windows)Typestring
    Defaultd:t:i:O,\mysqld.trace

    This variable indicates the current debugging settings. It is available only for servers built with debugging support. The initial value comes from the value of instances of the --debug option given at server startup. The global and session values may be set at runtime; the SUPER privilege is required, even for the session value.

    Assigning a value that begins with + or - cause the value to added to or subtracted from the current value:

    mysql> SET debug = 'T';
    mysql> SELECT @@debug;
    +---------+
    | @@debug |
    +---------+
    | T       |
    +---------+
    
    mysql> SET debug = '+P';
    mysql> SELECT @@debug;
    +---------+
    | @@debug |
    +---------+
    | P:T     |
    +---------+
    
    mysql> SET debug = '-P';
    mysql> SELECT @@debug;
    +---------+
    | @@debug |
    +---------+
    | T       |
    +---------+
    

    For more information, see Section 28.5.3, “The DBUG Package”.

  • debug_sync

    System VariableNamedebug_sync
    Variable ScopeSession
    Dynamic VariableYes
    Permitted ValuesTypestring

    This variable is the user interface to the Debug Sync facility. Use of Debug Sync requires that MySQL be configured with the -DENABLE_DEBUG_SYNC=1 CMake option (see Section 2.9.4, “MySQL Source-Configuration Options”). If Debug Sync is not compiled in, this system variable is not available.

    The global variable value is read only and indicates whether the facility is enabled. By default, Debug Sync is disabled and the value of debug_sync is OFF. If the server is started with --debug-sync-timeout=N, where N is a timeout value greater than 0, Debug Sync is enabled and the value of debug_sync is ON - current signal followed by the signal name. Also, N becomes the default timeout for individual synchronization points.

    The session value can be read by any user and will have the same value as the global variable. The session value can be set by users that have the SUPER privilege to control synchronization points.

    For a description of the Debug Sync facility and how to use synchronization points, see MySQL Internals: Test Synchronization.

  • default_authentication_plugin

    Introduced5.7.2
    Command-Line Format--default-authentication-plugin=plugin_name
    System VariableNamedefault_authentication_plugin
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeenumeration
    Defaultmysql_native_password
    Valid Valuesmysql_native_password
    sha256_password

    The default authentication plugin. Permitted values are mysql_native_password (use MySQL native passwords; this is the default) and sha256_password (use SHA-256 passwords). For more information about these plugins, see Section 7.5.1.1, “The Native Authentication Plugin”, and Section 7.5.1.4, “The SHA-256 Authentication Plugin”.

    Note

    If you use this variable to change the default authentication plugin to a value other than mysql_native_password, clients older than MySQL 5.5.6 will no longer be able to connect because they will not understand the resulting change to the authentication protocol.

    The value of default_authentication_plugin affects these aspects of server operation:

    • It determines which authentication plugin the server assigns to new accounts created by CREATE USER and GRANT statements that do not name a plugin explicitly with an IDENTIFIED WITH clause.

    • It sets the old_passwords system variable at startup to the value that is consistent with the password hashing method required by the default plugin. The old_passwords value affects hashing of passwords specified in the IDENTIFIED BY clause of CREATE USER and GRANT, and passwords specified as the argument to the PASSWORD() function.

    • For an account created with either of the following statements, the server associates the account with the default authentication plugin and assigns the account the given password, hashed according to the value of old_passwords.

      CREATE USER ... IDENTIFIED BY 'cleartext password';
      GRANT ...  IDENTIFIED BY 'cleartext password';
      
    • For an account created with either of the following statements, the statement fails if the password hash is not encrypted using the hash format required by the default authentication plugin. Otherwise, the server associates the account with the default authentication plugin and assigns the account the given password hash.

      CREATE USER ... IDENTIFIED BY PASSWORD 'encrypted password';
      GRANT ...  IDENTIFIED BY PASSWORD 'encrypted password';
      

    This variable was added in MySQL 5.7.2. Earlier in MySQL 5.7, use the --default-authentication-plugin command-line option instead, which is used the same way at server startup, but cannot be accessed at runtime.

  • default_password_lifetime

    Introduced5.7.4
    Command-Line Format--default_password_lifetime=#
    System VariableNamedefault_password_lifetime
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (<= 5.7.10)Typeinteger
    Default360
    Min Value0
    Max Value65535
    Permitted Values (>= 5.7.11)Typeinteger
    Default0
    Min Value0
    Max Value65535

    This variable defines the global automatic password expiration policy. It applies to accounts that use MySQL built-in authentication methods (accounts that use an authentication plugin of mysql_native_password, mysql_old_password, or sha256_password).

    The default default_password_lifetime value is 0, which disables automatic password expiration. If the value of default_password_lifetime is a positive integer N, it indicates the permitted password lifetime; passwords must be changed every N days.

    The global password expiration policy can be overridden as desired for individual accounts using the ALTER USER statement. See Section 7.3.6, “Password Expiration Policy”.

    Note

    From MySQL 5.7.4 to 5.7.10, the default default_password_lifetime value is 360 (passwords must be changed approximately once per year). For those versions, be aware that, if you make no changes to the default_password_lifetime variable or to individual user accounts, all user passwords will expire after 360 days, and all user accounts will start running in restricted mode when this happens. Clients (which are effectively users) connecting to the server will then get an error indicating that the password must be changed: ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.

    However, this is easy to miss for clients that automatically connect to the server, such as connections made from scripts. To avoid having such clients suddenly stop working due to a password expiring, make sure to change the password expiration settings for those clients, like this:

    ALTER USER 'script'@'localhost' PASSWORD EXPIRE NEVER

    Alternatively, set the default_password_lifetime variable to 0, thus disabling automatic password expiration for all users.

  • default_storage_engine

    Command-Line Format--default-storage-engine=name
    System VariableNamedefault_storage_engine
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultInnoDB

    The default storage engine. This variable sets the storage engine for permanent tables only. To set the storage engine for TEMPORARY tables, set the default_tmp_storage_engine system variable.

    To see which storage engines are available and enabled, use the SHOW ENGINES statement or query the INFORMATION_SCHEMA ENGINES table.

    default_storage_engine should be used in preference to storage_engine, which is deprecated and was removed in MySQL 5.7.5.

    If you disable the default storage engine at server startup, you must set the default engine for both permanent and TEMPORARY tables to a different engine or the server will not start.

  • default_tmp_storage_engine

    Command-Line Format--default_tmp_storage_engine=name
    System VariableNamedefault_tmp_storage_engine
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultInnoDB

    The default storage engine for TEMPORARY tables (created with CREATE TEMPORARY TABLE). To set the storage engine for permanent tables, set the default_storage_engine system variable. Also see the discussion of that variable regarding possible values.

    If you disable the default storage engine at server startup, you must set the default engine for both permanent and TEMPORARY tables to a different engine or the server will not start.

  • default_week_format

    Command-Line Format--default_week_format=#
    System VariableNamedefault_week_format
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value7

    The default mode value to use for the WEEK() function. See Section 13.7, “Date and Time Functions”.

  • delay_key_write

    Command-Line Format--delay-key-write[=name]
    System VariableNamedelay_key_write
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultON
    Valid ValuesON
    OFF
    ALL

    This option applies only to MyISAM tables. It can have one of the following values to affect handling of the DELAY_KEY_WRITE table option that can be used in CREATE TABLE statements.

    OptionDescription
    OFFDELAY_KEY_WRITE is ignored.
    ONMySQL honors any DELAY_KEY_WRITE option specified in CREATE TABLE statements. This is the default value.
    ALLAll new opened tables are treated as if they were created with the DELAY_KEY_WRITE option enabled.

    If DELAY_KEY_WRITE is enabled for a table, the key buffer is not flushed for the table on every index update, but only when the table is closed. This speeds up writes on keys a lot, but if you use this feature, you should add automatic checking of all MyISAM tables by starting the server with the --myisam-recover-options option (for example, --myisam-recover-options=BACKUP,FORCE). See Section 6.1.4, “Server Command Options”, and Section 16.2.1, “MyISAM Startup Options”.

    Warning

    If you enable external locking with --external-locking, there is no protection against index corruption for tables that use delayed key writes.

  • delayed_insert_limit

    Deprecated5.6.7
    Command-Line Format--delayed_insert_limit=#
    System VariableNamedelayed_insert_limit
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default100
    Min Value1
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default100
    Min Value1
    Max Value18446744073709551615

    This system variable is deprecated (because DELAYED inserts are not supported), and will be removed in a future release.

  • delayed_insert_timeout

    Deprecated5.6.7
    Command-Line Format--delayed_insert_timeout=#
    System VariableNamedelayed_insert_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default300

    This system variable is deprecated (because DELAYED inserts are not supported), and will be removed in a future release.

  • delayed_queue_size

    Deprecated5.6.7
    Command-Line Format--delayed_queue_size=#
    System VariableNamedelayed_queue_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default1000
    Min Value1
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default1000
    Min Value1
    Max Value18446744073709551615

    This system variable is deprecated (because DELAYED inserts are not supported), and will be removed in a future release.

  • disabled_storage_engines

    Introduced5.7.8
    Command-Line Format--disabled_storage_engines=engine[,engine]...
    System VariableNamedisabled_storage_engines
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring
    Defaultempty string

    This variable indicates which storage engines cannot be used to create tables or tablespaces. For example, to prevent new MyISAM or FEDERATED tables from being created, start the server with these lines in the server option file:

    [mysqld]
    disabled_storage_engines="MyISAM,FEDERATED"
    

    By default, disabled_storage_engines is empty (no engines disabled), but it can be set to a comma-separated list of one or more engines (not case sensitive). Any engine named in the value cannot be used to create tables or tablespaces with CREATE TABLE or CREATE TABLESPACE, and cannot be used with ALTER TABLE ... ENGINE or ALTER TABLESPACE ... ENGINE to change the storage engine of existing tables or tablespaces. Attempts to do so result in an ER_DISABLED_STORAGE_ENGINE error.

    disabled_storage_engines does not restrict other DDL statements for existing tables, such as CREATE INDEX, TRUNCATE TABLE, ANALYZE TABLE, DROP TABLE, or DROP TABLESPACE. This permits a smooth transition so that existing tables or tablespaces that use a disabled engine can be migrated to a permitted engine by means such as ALTER TABLE ... ENGINE permitted_engine.

    It is permitted to set the default_storage_engine or default_tmp_storage_engine system variable to a storage engine that is disabled. This could cause applications to behave erratically or fail, although that might be a useful technique in a development environment for identifying applications that use disabled engines, so that they can be modified.

    disabled_storage_engines is disabled and has no effect if the server is started with any of these options: --bootstrap, --initialize, --initialize-insecure, --skip-grant-tables.

  • disconnect_on_expired_password

    Introduced5.7.1
    Command-Line Format--disconnect_on_expired_password[=#]
    System VariableNamedisconnect_on_expired_password
    Variable ScopeSession
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultON

    This variable controls how the server handles clients with expired passwords:

    For more information about the interaction of client and server settings relating to expired-password handling, see Section 7.3.7, “Password Expiration and Sandbox Mode”.

  • div_precision_increment

    Command-Line Format--div_precision_increment=#
    System VariableNamediv_precision_increment
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default4
    Min Value0
    Max Value30

    This variable indicates the number of digits by which to increase the scale of the result of division operations performed with the / operator. The default value is 4. The minimum and maximum values are 0 and 30, respectively. The following example illustrates the effect of increasing the default value.

    mysql> SELECT 1/7;
    +--------+
    | 1/7    |
    +--------+
    | 0.1429 |
    +--------+
    mysql> SET div_precision_increment = 12;
    mysql> SELECT 1/7;
    +----------------+
    | 1/7            |
    +----------------+
    | 0.142857142857 |
    +----------------+
    
  • end_markers_in_json

    System VariableNameend_markers_in_json
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Whether optimizer JSON output should add end markers. See MySQL Internals: The end_markers_in_json System Variable.

  • eq_range_index_dive_limit

    System VariableNameeq_range_index_dive_limit
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (<= 5.7.3)Typeinteger
    Default10
    Min Value0
    Max Value4294967295
    Permitted Values (>= 5.7.4)Typeinteger
    Default200
    Min Value0
    Max Value4294967295

    This variable indicates the number of equality ranges in an equality comparison condition when the optimizer should switch from using index dives to index statistics in estimating the number of qualifying rows. It applies to evaluation of expressions that have either of these equivalent forms, where the optimizer uses a nonunique index to look up col_name values:

    col_name IN(val1, ..., valN)
    col_name = val1 OR ... OR col_name = valN
    

    In both cases, the expression contains N equality ranges. The optimizer can make row estimates using index dives or index statistics. If eq_range_index_dive_limit is greater than 0, the optimizer uses existing index statistics instead of index dives if there are eq_range_index_dive_limit or more equality ranges. Thus, to permit use of index dives for up to N equality ranges, set eq_range_index_dive_limit to N + 1. To disable use of index statistics and always use index dives regardless of N, set eq_range_index_dive_limit to 0.

    For more information, see Section 9.2.1.2.3, “Equality Range Optimization of Many-Valued Comparisons”.

    To update table index statistics for best estimates, use ANALYZE TABLE.

  • error_count

    The number of errors that resulted from the last statement that generated messages. This variable is read only. See Section 14.7.5.17, “SHOW ERRORS Syntax”.

  • event_scheduler

    Command-Line Format--event-scheduler[=value]
    System VariableNameevent_scheduler
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultOFF
    Valid ValuesON
    OFF
    DISABLED

    This variable indicates the status of the Event Scheduler; possible values are ON, OFF, and DISABLED, with the default being OFF. This variable and its effects on the Event Scheduler's operation are discussed in greater detail in the Overview section of the Events chapter.

  • expire_logs_days

    Command-Line Format--expire_logs_days=#
    System VariableNameexpire_logs_days
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value99

    The number of days for automatic binary log file removal. The default is 0, which means no automatic removal. Possible removals happen at startup and when the binary log is flushed. Log flushing occurs as indicated in Section 6.4, “MySQL Server Logs”.

    To remove binary log files manually, use the PURGE BINARY LOGS statement. See Section 14.4.1.1, “PURGE BINARY LOGS Syntax”.

  • explicit_defaults_for_timestamp

    Deprecated5.6.6
    Command-Line Format--explicit_defaults_for_timestamp=#
    System VariableNameexplicit_defaults_for_timestamp
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultFALSE

    In MySQL, the TIMESTAMP data type differs in nonstandard ways from other data types:

    • TIMESTAMP columns not explicitly declared with the NULL attribute are assigned the NOT NULL attribute. (Columns of other data types, if not explicitly declared as NOT NULL, permit NULL values.) Setting such a column to NULL sets it to the current timestamp.

    • The first TIMESTAMP column in a table, if not declared with the NULL attribute or an explicit DEFAULT or ON UPDATE clause, is automatically assigned the DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP attributes.

    • TIMESTAMP columns following the first one, if not declared with the NULL attribute or an explicit DEFAULT clause, are automatically assigned DEFAULT '0000-00-00 00:00:00' (the zero timestamp). For inserted rows that specify no explicit value for such a column, the column is assigned '0000-00-00 00:00:00' and no warning occurs.

    Those nonstandard behaviors remain the default for TIMESTAMP but as of MySQL 5.6.6 are deprecated and this warning appears at startup:

    [Warning] TIMESTAMP with implicit DEFAULT value is deprecated.
    Please use --explicit_defaults_for_timestamp server option (see
    documentation for more details).
    

    As indicated by the warning, to turn off the nonstandard behaviors, enable the explicit_defaults_for_timestamp system variable at server startup. With this variable enabled, the server handles TIMESTAMP as follows instead:

    • TIMESTAMP columns not explicitly declared as NOT NULL permit NULL values. Setting such a column to NULL sets it to NULL, not the current timestamp.

    • No TIMESTAMP column is assigned the DEFAULT CURRENT_TIMESTAMP or ON UPDATE CURRENT_TIMESTAMP attributes automatically. Those attributes must be explicitly specified.

    • TIMESTAMP columns declared as NOT NULL and without an explicit DEFAULT clause are treated as having no default value. For inserted rows that specify no explicit value for such a column, the result depends on the SQL mode. If strict SQL mode is enabled, an error occurs. If strict SQL mode is not enabled, the column is assigned the implicit default of '0000-00-00 00:00:00' and a warning occurs. This is similar to how MySQL treats other temporal types such as DATETIME.

    Note

    explicit_defaults_for_timestamp is itself deprecated because its only purpose is to permit control over now-deprecated TIMESTAMP behaviors that will be removed in a future MySQL release. When that removal occurs, explicit_defaults_for_timestamp will have no purpose and will be removed as well.

  • external_user

    System VariableNameexternal_user
    Variable ScopeSession
    Dynamic VariableNo
    Permitted ValuesTypestring

    The external user name used during the authentication process, as set by the plugin used to authenticate the client. With native (built-in) MySQL authentication, or if the plugin does not set the value, this variable is NULL. See Section 7.3.9, “Proxy Users”.

  • flush

    Command-Line Format--flush
    System VariableNameflush
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    If ON, the server flushes (synchronizes) all changes to disk after each SQL statement. Normally, MySQL does a write of all changes to disk only after each SQL statement and lets the operating system handle the synchronizing to disk. See Section B.5.3.3, “What to Do If MySQL Keeps Crashing”. This variable is set to ON if you start mysqld with the --flush option.

  • flush_time

    Command-Line Format--flush_time=#
    System VariableNameflush_time
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Permitted Values (Windows)Typeinteger
    Default0
    Min Value0

    If this is set to a nonzero value, all tables are closed every flush_time seconds to free up resources and synchronize unflushed data to disk. This option is best used only on systems with minimal resources.

  • foreign_key_checks

    If set to 1 (the default), foreign key constraints for InnoDB tables are checked. If set to 0, foreign key constraints are ignored, with a couple of exceptions. When re-creating a table that was dropped, an error is returned if the table definition does not conform to the foreign key constraints referencing the table. Likewise, an ALTER TABLE operation returns an error if a foreign key definition is incorrectly formed. For more information, see Section 14.1.18.5, “Using FOREIGN KEY Constraints”.

    Setting this variable has the same effect on NDB tables as it does for InnoDB tables. Typically you leave this setting enabled during normal operation, to enforce referential integrity. Disabling foreign key checking can be useful for reloading InnoDB tables in an order different from that required by their parent/child relationships. See Section 15.8.7, “InnoDB and FOREIGN KEY Constraints”.

    Setting foreign_key_checks to 0 also affects data definition statements: DROP SCHEMA drops a schema even if it contains tables that have foreign keys that are referred to by tables outside the schema, and DROP TABLE drops tables that have foreign keys that are referred to by other tables.

    Note

    Setting foreign_key_checks to 1 does not trigger a scan of the existing table data. Therefore, rows added to the table while foreign_key_checks=0 will not be verified for consistency.

    As of MySQL 5.7.5, dropping an index required by a foreign key constraint is not permitted, even with foreign_key_checks=0. The foreign key constraint must be removed before dropping the index (Bug #70260).

  • ft_boolean_syntax

    Command-Line Format--ft_boolean_syntax=name
    System VariableNameft_boolean_syntax
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypestring
    Default+ -><()~*:""&|

    The list of operators supported by boolean full-text searches performed using IN BOOLEAN MODE. See Section 13.9.2, “Boolean Full-Text Searches”.

    The default variable value is '+ -><()~*:""&|'. The rules for changing the value are as follows:

    • Operator function is determined by position within the string.

    • The replacement value must be 14 characters.

    • Each character must be an ASCII nonalphanumeric character.

    • Either the first or second character must be a space.

    • No duplicates are permitted except the phrase quoting operators in positions 11 and 12. These two characters are not required to be the same, but they are the only two that may be.

    • Positions 10, 13, and 14 (which by default are set to :, &, and |) are reserved for future extensions.

  • ft_max_word_len

    Command-Line Format--ft_max_word_len=#
    System VariableNameft_max_word_len
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Min Value10

    The maximum length of the word to be included in a MyISAM FULLTEXT index.

    Note

    FULLTEXT indexes on MyISAM tables must be rebuilt after changing this variable. Use REPAIR TABLE tbl_name QUICK.

  • ft_min_word_len

    Command-Line Format--ft_min_word_len=#
    System VariableNameft_min_word_len
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default4
    Min Value1

    The minimum length of the word to be included in a MyISAM FULLTEXT index.

    Note

    FULLTEXT indexes on MyISAM tables must be rebuilt after changing this variable. Use REPAIR TABLE tbl_name QUICK.

  • ft_query_expansion_limit

    Command-Line Format--ft_query_expansion_limit=#
    System VariableNameft_query_expansion_limit
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default20
    Min Value0
    Max Value1000

    The number of top matches to use for full-text searches performed using WITH QUERY EXPANSION.

  • ft_stopword_file

    Command-Line Format--ft_stopword_file=file_name
    System VariableNameft_stopword_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name

    The file from which to read the list of stopwords for full-text searches on MyISAM tables. The server looks for the file in the data directory unless an absolute path name is given to specify a different directory. All the words from the file are used; comments are not honored. By default, a built-in list of stopwords is used (as defined in the storage/myisam/ft_static.c file). Setting this variable to the empty string ('') disables stopword filtering. See also Section 13.9.4, “Full-Text Stopwords”.

    Note

    FULLTEXT indexes on MyISAM tables must be rebuilt after changing this variable or the contents of the stopword file. Use REPAIR TABLE tbl_name QUICK.

  • general_log

    Command-Line Format--general-log
    System VariableNamegeneral_log
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Whether the general query log is enabled. The value can be 0 (or OFF) to disable the log or 1 (or ON) to enable the log. The default value depends on whether the --general_log option is given. The destination for log output is controlled by the log_output system variable; if that value is NONE, no log entries are written even if the log is enabled.

  • general_log_file

    Command-Line Format--general-log-file=file_name
    System VariableNamegeneral_log_file
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypefile name
    Defaulthost_name.log

    The name of the general query log file. The default value is host_name.log, but the initial value can be changed with the --general_log_file option.

  • group_concat_max_len

    Command-Line Format--group_concat_max_len=#
    System VariableNamegroup_concat_max_len
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default1024
    Min Value4
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default1024
    Min Value4
    Max Value18446744073709551615

    The maximum permitted result length in bytes for the GROUP_CONCAT() function. The default is 1024.

  • have_compress

    YES if the zlib compression library is available to the server, NO if not. If not, the COMPRESS() and UNCOMPRESS() functions cannot be used.

  • have_crypt

    YES if the crypt() system call is available to the server, NO if not. If not, the ENCRYPT() function cannot be used.

  • have_dynamic_loading

    YES if mysqld supports dynamic loading of plugins, NO if not. If the value is NO, you cannot use options such as --plugin-load to load plugins at server startup, or the INSTALL PLUGIN statement to load plugins at runtime.

  • have_geometry

    YES if the server supports spatial data types, NO if not.

  • have_openssl

    This variable is an alias for have_ssl.

  • have_profiling

    YES if statement profiling capability is present, NO if not. If present, the profiling system variable controls whether this capability is enabled or disabled. See Section 14.7.5.31, “SHOW PROFILES Syntax”.

    This variable is deprecated and will be removed in a future MySQL release.

  • have_query_cache

    YES if mysqld supports the query cache, NO if not.

  • have_rtree_keys

    YES if RTREE indexes are available, NO if not. (These are used for spatial indexes in MyISAM tables.)

  • have_ssl

    YES if mysqld supports SSL connections, NO if not. DISABLED indicates that the server was compiled with SSL support, but was not started with the appropriate --ssl-xxx options. For more information, see Section 7.4.2, “Building MySQL with Support for Secure Connections”.

  • have_statement_timeout

    Introduced5.7.4
    System VariableNamehave_statement_timeout
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean

    Whether the statement execution timeout feature is available (see Statement Execution Time Optimizer Hints). The value can be NO if the background thread used by this feature could not be initialized.

  • have_symlink

    YES if symbolic link support is enabled, NO if not. This is required on Unix for support of the DATA DIRECTORY and INDEX DIRECTORY table options. If the server is started with the --skip-symbolic-links option, the value is DISABLED.

    This variable has no meaning on Windows.

  • host_cache_size

    System VariableNamehost_cache_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default-1 (autosized)
    Min Value0
    Max Value65536

    The size of the internal host cache (see Section 9.12.5.2, “DNS Lookup Optimization and the Host Cache”). Setting the size to 0 disables the host cache. Changing the cache size at runtime implicitly causes a FLUSH HOSTS operation to clear the host cache and truncate the host_cache table.

    The default value is 128, plus 1 for a value of max_connections up to 500, plus 1 for every increment of 20 over 500 in the max_connections value, capped to a limit of 2000.

    Use of --skip-host-cache is similar to setting the host_cache_size system variable to 0, but host_cache_size is more flexible because it can also be used to resize, enable, or disable the host cache at runtime, not just at server startup.

    If you start the server with --skip-host-cache, that does not prevent changes to the value of host_cache_size, but such changes have no effect and the cache is not re-enabled even if host_cache_size is set larger than 0.

  • hostname

    System VariableNamehostname
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring

    The server sets this variable to the server host name at startup.

  • identity

    This variable is a synonym for the last_insert_id variable. It exists for compatibility with other database systems. You can read its value with SELECT @@identity, and set it using SET identity.

  • ignore_db_dirs

    System VariableNameignore_db_dirs
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring

    A comma-separated list of names that are not considered as database directories in the data directory. The value is set from any instances of --ignore-db-dir given at server startup.

    As of MySQL 5.7.11, --ignore-db-dir can be used at data directory initialization time with mysqld --initialize to specify directories that the server should ignore for purposes of assessing whether an existing data directory is considered empty. See Section 2.10.1.1, “Initializing the Data Directory Manually Using mysqld”.

  • init_connect

    Command-Line Format--init-connect=name
    System VariableNameinit_connect
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypestring

    A string to be executed by the server for each client that connects. The string consists of one or more SQL statements, separated by semicolon characters. For example, each client session begins by default with autocommit mode enabled. For older servers (before MySQL 5.5.8), there is no global autocommit system variable to specify that autocommit should be disabled by default, but as a workaround init_connect can be used to achieve the same effect:

    SET GLOBAL init_connect='SET autocommit=0';
    

    The init_connect variable can also be set on the command line or in an option file. To set the variable as just shown using an option file, include these lines:

    [mysqld]
    init_connect='SET autocommit=0'
    

    For users that have the SUPER privilege, the content of init_connect is not executed. This is done so that an erroneous value for init_connect does not prevent all clients from connecting. For example, the value might contain a statement that has a syntax error, thus causing client connections to fail. Not executing init_connect for users that have the SUPER privilege enables them to open a connection and fix the init_connect value.

    The server discards any result sets produced by statements in the value of of init_connect.

  • init_file

    Command-Line Format--init-file=file_name
    System VariableNameinit_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name

    The name of the file specified with the --init-file option when you start the server. This should be a file containing SQL statements that you want the server to execute when it starts. Each statement must be on a single line and should not include comments. For more information, see the description of --init-file.

  • innodb_xxx

    InnoDB system variables are listed in Section 15.14, “InnoDB Startup Options and System Variables”. These variables control many aspects of storage, memory use, and I/O patterns for InnoDB tables, and are especially important now that InnoDB is the default storage engine.

  • insert_id

    The value to be used by the following INSERT or ALTER TABLE statement when inserting an AUTO_INCREMENT value. This is mainly used with the binary log.

  • interactive_timeout

    Command-Line Format--interactive_timeout=#
    System VariableNameinteractive_timeout
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default28800
    Min Value1

    The number of seconds the server waits for activity on an interactive connection before closing it. An interactive client is defined as a client that uses the CLIENT_INTERACTIVE option to mysql_real_connect(). See also wait_timeout.

  • internal_tmp_disk_storage_engine

    Introduced5.7.5
    Command-Line Format--internal_tmp_disk_storage_engine=#
    System VariableNameinternal_tmp_disk_storage_engine
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (5.7.5)Typeenumeration
    DefaultMYISAM
    Valid ValuesMYISAM
    INNODB
    Permitted Values (>= 5.7.6)Typeenumeration
    DefaultINNODB
    Valid ValuesMYISAM
    INNODB

    The storage engine for on-disk internal temporary tables (see Section 9.4.4, “Internal Temporary Table Use in MySQL”). Permitted values are MYISAM and INNODB.

    This variable was added in MySQL 5.7.5 with a default of MYISAM. In MySQL 5.7.6, the default value was changed to INNODB. With this change, the optimizer uses the InnoDB storage engine by default for on-disk internal temporary tables.

    Under internal_tmp_disk_storage_engine=INNODB, queries that generate temporary tables that exceed InnoDB row or column limits will return Row size too large or Too many columns errors. The workaround is to set internal_tmp_disk_storage_engine to MYISAM.

  • join_buffer_size

    Command-Line Format--join_buffer_size=#
    System VariableNamejoin_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (Windows)Typeinteger
    Default262144
    Min Value128
    Max Value4294967295
    Permitted Values (Other, 32-bit platforms)Typeinteger
    Default262144
    Min Value128
    Max Value4294967295
    Permitted Values (Other, 64-bit platforms)Typeinteger
    Default262144
    Min Value128
    Max Value18446744073709547520

    The minimum size of the buffer that is used for plain index scans, range index scans, and joins that do not use indexes and thus perform full table scans. Normally, the best way to get fast joins is to add indexes. Increase the value of join_buffer_size to get a faster full join when adding indexes is not possible. One join buffer is allocated for each full join between two tables. For a complex join between several tables for which indexes are not used, multiple join buffers might be necessary.

    Unless Batched Key Access (BKA) is used, there is no gain from setting the buffer larger than required to hold each matching row, and all joins allocate at least the minimum size, so use caution in setting this variable to a large value globally. It is better to keep the global setting small and change to a larger setting only in sessions that are doing large joins. Memory allocation time can cause substantial performance drops if the global size is larger than needed by most queries that use it.

    When BKA is used, the value of join_buffer_size defines how large the batch of keys is in each request to the storage engine. The larger the buffer, the more sequential access will be to the right hand table of a join operation, which can significantly improve performance.

    The default is 256KB. The maximum permissible setting for join_buffer_size is 4GB−1. Larger values are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB−1 with a warning).

    For additional information about join buffering, see Section 9.2.1.6, “Nested-Loop Join Algorithms”. For information about Batched Key Access, see Section 9.2.1.11, “Block Nested-Loop and Batched Key Access Joins”.

  • keep_files_on_create

    Command-Line Format--keep_files_on_create=#
    System VariableNamekeep_files_on_create
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    If a MyISAM table is created with no DATA DIRECTORY option, the .MYD file is created in the database directory. By default, if MyISAM finds an existing .MYD file in this case, it overwrites it. The same applies to .MYI files for tables created with no INDEX DIRECTORY option. To suppress this behavior, set the keep_files_on_create variable to ON (1), in which case MyISAM will not overwrite existing files and returns an error instead. The default value is OFF (0).

    If a MyISAM table is created with a DATA DIRECTORY or INDEX DIRECTORY option and an existing .MYD or .MYI file is found, MyISAM always returns an error. It will not overwrite a file in the specified directory.

  • key_buffer_size

    Command-Line Format--key_buffer_size=#
    System VariableNamekey_buffer_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default8388608
    Min Value8
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default8388608
    Min Value8
    Max ValueOS_PER_PROCESS_LIMIT

    Index blocks for MyISAM tables are buffered and are shared by all threads. key_buffer_size is the size of the buffer used for index blocks. The key buffer is also known as the key cache.

    The maximum permissible setting for key_buffer_size is 4GB−1 on 32-bit platforms. Larger values are permitted for 64-bit platforms. The effective maximum size might be less, depending on your available physical RAM and per-process RAM limits imposed by your operating system or hardware platform. The value of this variable indicates the amount of memory requested. Internally, the server allocates as much memory as possible up to this amount, but the actual allocation might be less.

    You can increase the value to get better index handling for all reads and multiple writes; on a system whose primary function is to run MySQL using the MyISAM storage engine, 25% of the machine's total memory is an acceptable value for this variable. However, you should be aware that, if you make the value too large (for example, more than 50% of the machine's total memory), your system might start to page and become extremely slow. This is because MySQL relies on the operating system to perform file system caching for data reads, so you must leave some room for the file system cache. You should also consider the memory requirements of any other storage engines that you may be using in addition to MyISAM.

    For even more speed when writing many rows at the same time, use LOCK TABLES. See Section 9.2.4.1, “Optimizing INSERT Statements”.

    You can check the performance of the key buffer by issuing a SHOW STATUS statement and examining the Key_read_requests, Key_reads, Key_write_requests, and Key_writes status variables. (See Section 14.7.5, “SHOW Syntax”.) The Key_reads/Key_read_requests ratio should normally be less than 0.01. The Key_writes/Key_write_requests ratio is usually near 1 if you are using mostly updates and deletes, but might be much smaller if you tend to do updates that affect many rows at the same time or if you are using the DELAY_KEY_WRITE table option.

    The fraction of the key buffer in use can be determined using key_buffer_size in conjunction with the Key_blocks_unused status variable and the buffer block size, which is available from the key_cache_block_size system variable:

    1 - ((Key_blocks_unused * key_cache_block_size) / key_buffer_size)
    

    This value is an approximation because some space in the key buffer is allocated internally for administrative structures. Factors that influence the amount of overhead for these structures include block size and pointer size. As block size increases, the percentage of the key buffer lost to overhead tends to decrease. Larger blocks results in a smaller number of read operations (because more keys are obtained per read), but conversely an increase in reads of keys that are not examined (if not all keys in a block are relevant to a query).

    It is possible to create multiple MyISAM key caches. The size limit of 4GB applies to each cache individually, not as a group. See Section 9.10.2, “The MyISAM Key Cache”.

  • key_cache_age_threshold

    Command-Line Format--key_cache_age_threshold=#
    System VariableNamekey_cache_age_threshold
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default300
    Min Value100
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default300
    Min Value100
    Max Value18446744073709551615

    This value controls the demotion of buffers from the hot sublist of a key cache to the warm sublist. Lower values cause demotion to happen more quickly. The minimum value is 100. The default value is 300. See Section 9.10.2, “The MyISAM Key Cache”.

  • key_cache_block_size

    Command-Line Format--key_cache_block_size=#
    System VariableNamekey_cache_block_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default1024
    Min Value512
    Max Value16384

    The size in bytes of blocks in the key cache. The default value is 1024. See Section 9.10.2, “The MyISAM Key Cache”.

  • key_cache_division_limit

    Command-Line Format--key_cache_division_limit=#
    System VariableNamekey_cache_division_limit
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default100
    Min Value1
    Max Value100

    The division point between the hot and warm sublists of the key cache buffer list. The value is the percentage of the buffer list to use for the warm sublist. Permissible values range from 1 to 100. The default value is 100. See Section 9.10.2, “The MyISAM Key Cache”.

  • large_files_support

    System VariableNamelarge_files_support
    Variable ScopeGlobal
    Dynamic VariableNo

    Whether mysqld was compiled with options for large file support.

  • large_pages

    Command-Line Format--large-pages
    System VariableNamelarge_pages
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform SpecificLinux
    Permitted Values (Linux)Typeboolean
    DefaultFALSE

    Whether large page support is enabled (via the --large-pages option). See Section 9.12.4.2, “Enabling Large Page Support”.

  • large_page_size

    System VariableNamelarge_page_size
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted Values (Linux)Typeinteger
    Default0

    If large page support is enabled, this shows the size of memory pages. Large memory pages are supported only on Linux; on other platforms, the value of this variable is always 0. See Section 9.12.4.2, “Enabling Large Page Support”.

  • last_insert_id

    The value to be returned from LAST_INSERT_ID(). This is stored in the binary log when you use LAST_INSERT_ID() in a statement that updates a table. Setting this variable does not update the value returned by the mysql_insert_id() C API function.

  • lc_messages

    Command-Line Format--lc-messages=name
    System VariableNamelc_messages
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring
    Defaulten_US

    The locale to use for error messages. The default is en_US. The server converts the argument to a language name and combines it with the value of lc_messages_dir to produce the location for the error message file. See Section 11.2, “Setting the Error Message Language”.

  • lc_messages_dir

    Command-Line Format--lc-messages-dir=dir_name
    System VariableNamelc_messages_dir
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name

    The directory where error messages are located. The server uses the value together with the value of lc_messages to produce the location for the error message file. See Section 11.2, “Setting the Error Message Language”.

  • lc_time_names

    System VariableNamelc_time_names
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring

    This variable specifies the locale that controls the language used to display day and month names and abbreviations. This variable affects the output from the DATE_FORMAT(), DAYNAME() and MONTHNAME() functions. Locale names are POSIX-style values such as 'ja_JP' or 'pt_BR'. The default value is 'en_US' regardless of your system's locale setting. For further information, see Section 11.7, “MySQL Server Locale Support”.

  • license

    System VariableNamelicense
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring
    DefaultGPL

    The type of license the server has.

  • local_infile

    System VariableNamelocal_infile
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    Defaulttrue

    Whether LOCAL is supported for LOAD DATA INFILE statements. If this variable is disabled, clients cannot use LOCAL in LOAD DATA statements. While the default for this variable is true, whether LOAD DATA INFILE LOCAL is actually permitted depends on how MySQL was compiled, as well as a number of settings on both the server and the client; see Section 7.1.6, “Security Issues with LOAD DATA LOCAL”, for details.

  • lock_wait_timeout

    Command-Line Format--lock_wait_timeout=#
    System VariableNamelock_wait_timeout
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default31536000
    Min Value1
    Max Value31536000

    This variable specifies the timeout in seconds for attempts to acquire metadata locks. The permissible values range from 1 to 31536000 (1 year). The default is 31536000.

    This timeout applies to all statements that use metadata locks. These include DML and DDL operations on tables, views, stored procedures, and stored functions, as well as LOCK TABLES, FLUSH TABLES WITH READ LOCK, and HANDLER statements.

    This timeout does not apply to implicit accesses to system tables in the mysql database, such as grant tables modified by GRANT or REVOKE statements or table logging statements. The timeout does apply to system tables accessed directly, such as with SELECT or UPDATE.

    The timeout value applies separately for each metadata lock attempt. A given statement can require more than one lock, so it is possible for the statement to block for longer than the lock_wait_timeout value before reporting a timeout error. When lock timeout occurs, ER_LOCK_WAIT_TIMEOUT is reported.

    lock_wait_timeout does not apply to delayed inserts, which always execute with a timeout of 1 year. This is done to avoid unnecessary timeouts because a session that issues a delayed insert receives no notification of delayed insert timeouts.

  • locked_in_memory

    System VariableNamelocked_in_memory
    Variable ScopeGlobal
    Dynamic VariableNo

    Whether mysqld was locked in memory with --memlock.

  • log_backward_compatible_user_definitions

    Introduced5.7.6
    Removed5.7.9
    Command-Line Format--log_backward_compatible_user_definitions[={OFF|ON}]
    System VariableNamelog_backward_compatible_user_definitions
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Whether to log the user_specification part of CREATE USER, ALTER USER, and GRANT statements in backward-compatible (pre-5.7.6) fashion:

    • By default, this variable is disabled. The server writes user specifications as user IDENTIFIED WITH auth_plugin AS 'hash_string'.

    • When enabled, the server writes user specifications as user IDENTIFIED BY PASSWORD 'hash_string'. Enabling this variable ensures better compatibility for cross-version replication.

    This variable was removed in MySQL 5.7.9 and replaced by log_builtin_as_identified_by_password.

  • log_bin_trust_function_creators

    Command-Line Format--log-bin-trust-function-creators
    System VariableNamelog_bin_trust_function_creators
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultFALSE

    This variable applies when binary logging is enabled. It controls whether stored function creators can be trusted not to create stored functions that will cause unsafe events to be written to the binary log. If set to 0 (the default), users are not permitted to create or alter stored functions unless they have the SUPER privilege in addition to the CREATE ROUTINE or ALTER ROUTINE privilege. A setting of 0 also enforces the restriction that a function must be declared with the DETERMINISTIC characteristic, or with the READS SQL DATA or NO SQL characteristic. If the variable is set to 1, MySQL does not enforce these restrictions on stored function creation. This variable also applies to trigger creation. See Section 23.7, “Binary Logging of Stored Programs”.

  • log_builtin_as_identified_by_password

    Introduced5.7.9
    Command-Line Format--log_builtin_as_identified_by_password[={OFF|ON}]
    System VariableNamelog_builtin_as_identified_by_password
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    This variable affects binary logging of user-management statements. If enabled, binary logging for CREATE USER statements involving built-in authentication plugins rewrites the statements to include an IDENTIFIED BY PASSWORD clause, and SET PASSWORD statements are logged as SET PASSWORD statements, rather than being rewritten to ALTER USER statements.

    This variable was added in MySQL 5.7.9. It replaces the log_backward_compatible_user_definitions variable.

  • log_error

    Command-Line Format--log-error[=file_name]
    System VariableNamelog_error
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name

    The location of the error log, or stderr if the server is writing error message to the standard error output. See Section 6.4.2, “The Error Log”.

  • log_error_verbosity

    Introduced5.7.2
    Command-Line Format--log_error_verbosity=#
    System VariableNamelog_error_verbosity
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default3
    Min Value1
    Max Value3

    This variable controls verbosity of the server in writing error, warning, and note messages to the error log. The following table shows the permitted values. The default is 3.

    Verbosity ValueMessage Types Logged
    1Errors only
    2Errors and warnings
    3Errors, warnings, and notes

    log_error_verbosity was added in MySQL 5.7.2. It is preferred over, and should be used instead of, the older log_warnings system variable. See the description of log_warnings for information about how that variable relates to log_error_verbosity. In particular, assigning a value to log_warnings assigns a value to log_error_verbosity and vice versa.

  • log_output

    Command-Line Format--log-output=name
    System VariableNamelog_output
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeset
    DefaultFILE
    Valid ValuesTABLE
    FILE
    NONE

    The destination for general query log and slow query log output. The value can be a comma-separated list of one or more of the words TABLE (log to tables), FILE (log to files), or NONE (do not log to tables or files). The default value is FILE. NONE, if present, takes precedence over any other specifiers. If the value is NONE log entries are not written even if the logs are enabled. If the logs are not enabled, no logging occurs even if the value of log_output is not NONE. For more information, see Section 6.4.1, “Selecting General Query and Slow Query Log Output Destinations”.

  • log_queries_not_using_indexes

    Command-Line Format--log-queries-not-using-indexes
    System VariableNamelog_queries_not_using_indexes
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Whether queries that do not use indexes are logged to the slow query log. See Section 6.4.5, “The Slow Query Log”.

  • log_syslog

    Introduced5.7.5
    Command-Line Format--log_syslog[={0|1}]
    System VariableNamelog_syslog
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (Unix)Typeboolean
    DefaultOFF
    Permitted Values (Windows)Typeboolean
    DefaultON

    Whether to write error log output to syslog (on Unix and Unix-like systems) or Event Log (on Windows). The default value is platform specific:

    • On Unix and Unix-like systems, syslog output is disabled by default.

    • On Windows, Event Log output is enabled by default, which is consistent with older MySQL versions.

    Regardless of the default, log_syslog can be set explicitly to control output on any supported platform.

    syslog output control is orthogonal to sending error output to a file or (on Windows) to the console. Error output can be directed to the latter destination in addition to or instead of syslog as desired. See Section 6.4.2, “The Error Log”.

  • log_syslog_facility

    Introduced5.7.5
    Command-Line Format--log_syslog_facility=value
    System VariableNamelog_syslog_facility
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypestring
    Defaultdaemon

    The facility for error log output written to syslog (what type of program is sending the message). This variable has no effect unless the log_syslog system variable is enabled. See Section 6.4.2, “The Error Log”.

    The permitted values can vary per operating system; consult your system syslog documentation.

    This variable does not exist on Windows.

  • log_syslog_include_pid

    Introduced5.7.5
    Command-Line Format--log_syslog_include_pid[={0|1}]
    System VariableNamelog_syslog_include_pid
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultON

    Whether to include the server process ID in each line of error log output written to syslog. This variable has no effect unless the log_syslog system variable is enabled. See Section 6.4.2, “The Error Log”.

    This variable does not exist on Windows.

  • log_syslog_tag

    Introduced5.7.5
    Command-Line Format--log_syslog_tag=value
    System VariableNamelog_syslog_tag
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypestring
    Defaultempty string

    The tag to be added to the server identifier in error log output written to syslog. This variable has no effect unless the log_syslog system variable is enabled. See Section 6.4.2, “The Error Log”.

    By default, the server identifier is mysqld with no tag. If a tag of tag_val is specified, it is appended to the server identifier with a leading hyphen, resulting in an identifier of mysqld-tag_val.

    On Windows, to use a tag that does not already exist, the server must be run from an account with Administrator privileges, to permit creation of a registry entry for the tag. Elevated privileges are not required if the tag already exists.

  • log_timestamps

    Introduced5.7.2
    Command-Line Format--log_timestamps=#
    System VariableNamelog_timestamps
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultUTC
    Valid ValuesUTC
    SYSTEM

    This variable controls the timestamp time zone of error log messages, and of general query log and slow query log messages written to files. It does not affect the time zone of general query log and slow query log messages written to tables (mysql.general_log, mysql.slow_log). Rows retrieved from those tables can be converted from the local system time zone to any desired time zone with CONVERT_TZ() or by setting the session time_zone system variable.

    Permitted log_timestamps values are UTC (the default) and SYSTEM (local system time zone).

    Timestamps are written using ISO 8601 / RFC 3339 format: YYYY-MM-DDThh:mm:ss.uuuuuu plus a tail value of Z signifying Zulu time (UTC) or ±hh:mm (an offset from UTC).

    This variable was added in MySQL 5.7.2. Before 5.7.2, timestamps in log messages were written using the local system time zone by default, not UTC. If you want the previous log message time zone default, set log_timestamps=SYSTEM.

  • log_throttle_queries_not_using_indexes

    System VariableNamelog_throttle_queries_not_using_indexes
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0

    If log_queries_not_using_indexes is enabled, the log_throttle_queries_not_using_indexes variable limits the number of such queries per minute that can be written to the slow query log. A value of 0 (the default) means no limit. For more information, see Section 6.4.5, “The Slow Query Log”.

  • log_slow_admin_statements

    Introduced5.7.1
    System VariableNamelog_slow_admin_statements
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Include slow administrative statements in the statements written to the slow query log. Administrative statements include ALTER TABLE, ANALYZE TABLE, CHECK TABLE, CREATE INDEX, DROP INDEX, OPTIMIZE TABLE, and REPAIR TABLE.

  • log_warnings

    Deprecated5.7.2
    Command-Line Format--log-warnings[=#]
    System VariableNamelog_warnings
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms, <= 5.7.1)Typeinteger
    Default1
    Min Value0
    Max Value4294967295
    Permitted Values (32-bit platforms, >= 5.7.2)Typeinteger
    Default2
    Min Value0
    Max Value4294967295
    Permitted Values (64-bit platforms, <= 5.7.1)Typeinteger
    Default1
    Min Value0
    Max Value18446744073709551615
    Permitted Values (64-bit platforms, >= 5.7.2)Typeinteger
    Default2
    Min Value0
    Max Value18446744073709551615

    Whether to produce additional warning messages to the error log. This variable is enabled by default (the default is 1 before MySQL 5.7.2, 2 as of 5.7.2). To disable it, set it to 0. The server logs messages about statements that are unsafe for statement-based logging if the value is greater than 0. Aborted connections and access-denied errors for new connection attempts are logged if the value is greater than 1. See Section B.5.2.11, “Communication Errors and Aborted Connections”.

    Enabling this option by setting it greater than 0 is recommended, if you use replication, to get more information about what is happening, such as messages about network failures and reconnections. If the value is greater than 1, aborted connections are written to the error log, and access-denied errors for new connection attempts are written.

    If a slave server is started with log_warnings enabled, the slave prints messages to the error log to provide information about its status, such as the binary log and relay log coordinates where it starts its job, when it is switching to another relay log, when it reconnects after a disconnect, and so forth.

    As of MySQL 5.7.2, information items previously governed by log_warnings are governed by log_error_verbosity, which is preferred over, and should be used instead of, the older log_warnings system variable. (The log_warnings system variable and --log-warnings command-line option are deprecated and will be removed in a future MySQL release.)

    Assigning a value to log_warnings assigns a value to log_error_verbosity and vice versa. The variables are related as follows:

    As of MySQL 5.7.2, the default log level is controlled by log_error_verbosity, which has a default of 3. In addition, the default for log_warnings changes from 1 to 2, which corresponds to log_error_verbosity=3. To achieve a logging level similar to the previous default, set log_error_verbosity=2.

    In MySQL 5.7.2 and higher, use of log_warnings is still permitted but maps onto use of log_error_verbosity as follows:

  • long_query_time

    Command-Line Format--long_query_time=#
    System VariableNamelong_query_time
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypenumeric
    Default10
    Min Value0

    If a query takes longer than this many seconds, the server increments the Slow_queries status variable. If the slow query log is enabled, the query is logged to the slow query log file. This value is measured in real time, not CPU time, so a query that is under the threshold on a lightly loaded system might be above the threshold on a heavily loaded one. The minimum and default values of long_query_time are 0 and 10, respectively. The value can be specified to a resolution of microseconds. For logging to a file, times are written including the microseconds part. For logging to tables, only integer times are written; the microseconds part is ignored. See Section 6.4.5, “The Slow Query Log”.

  • low_priority_updates

    Command-Line Format--low-priority-updates
    System VariableNamelow_priority_updates
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultFALSE

    If set to 1, all INSERT, UPDATE, DELETE, and LOCK TABLE WRITE statements wait until there is no pending SELECT or LOCK TABLE READ on the affected table. This affects only storage engines that use only table-level locking (such as MyISAM, MEMORY, and MERGE).

  • lower_case_file_system

    System VariableNamelower_case_file_system
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean

    This variable describes the case sensitivity of file names on the file system where the data directory is located. OFF means file names are case sensitive, ON means they are not case sensitive. This variable is read only because it reflects a file system attribute and setting it would have no effect on the file system.

  • lower_case_table_names

    Command-Line Format--lower_case_table_names[=#]
    System VariableNamelower_case_table_names
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value2

    If set to 0, table names are stored as specified and comparisons are case sensitive. If set to 1, table names are stored in lowercase on disk and comparisons are not case sensitive. If set to 2, table names are stored as given but compared in lowercase. This option also applies to database names and table aliases. For additional information, see Section 10.2.2, “Identifier Case Sensitivity”.

    On Windows the default value is 1. On OS X, the default value is 2.

    You should not set lower_case_table_names to 0 if you are running MySQL on a system where the data directory resides on a case-insensitive file system (such as on Windows or OS X). It is an unsupported combination that could result in a hang condition when running an INSERT INTO ... SELECT ... FROM tbl_name operation with the wrong tbl_name letter case. With MyISAM, accessing table names using different letter cases could cause index corruption.

    As of MySQL 5.7.9, an error message is printed and the server exits if you attempt to start the server with --lower_case_table_names=0 on a case-insensitive file system.

    If you are using InnoDB tables, you should set this variable to 1 on all platforms to force names to be converted to lowercase.

    The setting of this variable in MySQL 5.7 affects the behavior of replication filtering options with regard to case sensitivity. (Bug #51639) See Section 18.2.5, “How Servers Evaluate Replication Filtering Rules”, for more information.

  • max_allowed_packet

    Command-Line Format--max_allowed_packet=#
    System VariableNamemax_allowed_packet
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default4194304
    Min Value1024
    Max Value1073741824

    The maximum size of one packet or any generated/intermediate string, or any parameter sent by the mysql_stmt_send_long_data() C API function. The default is 4MB.

    The packet message buffer is initialized to net_buffer_length bytes, but can grow up to max_allowed_packet bytes when needed. This value by default is small, to catch large (possibly incorrect) packets.

    You must increase this value if you are using large BLOB columns or long strings. It should be as big as the largest BLOB you want to use. The protocol limit for max_allowed_packet is 1GB. The value should be a multiple of 1024; nonmultiples are rounded down to the nearest multiple.

    When you change the message buffer size by changing the value of the max_allowed_packet variable, you should also change the buffer size on the client side if your client program permits it. The default max_allowed_packet value built in to the client library is 1GB, but individual client programs might override this. For example, mysql and mysqldump have defaults of 16MB and 24MB, respectively. They also enable you to change the client-side value by setting max_allowed_packet on the command line or in an option file.

    The session value of this variable is read only. The client can receive up to as many bytes as the session value. However, the server will not send to the client more bytes than the current global max_allowed_packet value. (The global value could be less than the session value if the global value is changed after the client connects.)

  • max_connect_errors

    Command-Line Format--max_connect_errors=#
    System VariableNamemax_connect_errors
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default100
    Min Value1
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default100
    Min Value1
    Max Value18446744073709551615

    If more than this many successive connection requests from a host are interrupted without a successful connection, the server blocks that host from further connections. You can unblock blocked hosts by flushing the host cache. To do so, issue a FLUSH HOSTS statement or execute a mysqladmin flush-hosts command. If a connection is established successfully within fewer than max_connect_errors attempts after a previous connection was interrupted, the error count for the host is cleared to zero. However, once a host is blocked, flushing the host cache is the only way to unblock it. The default is 100.

  • max_connections

    Command-Line Format--max_connections=#
    System VariableNamemax_connections
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default151
    Min Value1
    Max Value100000

    The maximum permitted number of simultaneous client connections. By default, this is 151. See Section B.5.2.7, “Too many connections”, for more information.

    Increasing this value increases the number of file descriptors that mysqld requires. If the required number of descriptors are not available, the server reduces the value of max_connections. See Section 9.4.3.1, “How MySQL Opens and Closes Tables”, for comments on file descriptor limits.

    Connections refused because the max_connections limit is reached increment the Connection_errors_max_connections status variable.

  • max_delayed_threads

    Deprecated5.6.7
    Command-Line Format--max_delayed_threads=#
    System VariableNamemax_delayed_threads
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default20
    Min Value0
    Max Value16384

    This system variable is deprecated (because DELAYED inserts are not supported), and will be removed in a future release.

  • max_digest_length

    Introduced5.7.6
    Command-Line Format--max_digest_length=#
    System VariableNamemax_digest_length
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default1024
    Min Value0
    Max Value1048576

    The maximum number of bytes available for computing statement digests (see Section 25.8, “Performance Schema Statement Digests”). Once this amount of space is used during digest computation for a statement, no further tokens from the parsed statement are collected or figure into the digest value. Statements that differ only after that many bytes of parsed statement tokens produce the same digest and are considered identical if compared or if aggregated for digest statistics.

    Decreasing the max_digest_length value reduces memory use but causes the digest value of more statements to become indistinguishable if they differ only at the end. Increasing the value permits longer statements to be distinguished but increases memory use, particularly for workloads that involve large numbers of simultaneous sessions (max_digest_length bytes are allocated per session).

    The parser uses this system variable as a limit on the maximum length of digests that it computes. If the Performance Schema tracks statement events, it makes a copy of the digest value, using the performance_schema_max_digest_length. system variable as a limit on the maximum length of digests that it stores. Consequently, if performance_schema_max_digest_length is less than max_digest_length, digest values stored in the Performance Schema may be further truncated relative to the original digest values.

  • max_error_count

    Command-Line Format--max_error_count=#
    System VariableNamemax_error_count
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default64
    Min Value0
    Max Value65535

    The maximum number of error, warning, and note messages to be stored for display by the SHOW ERRORS and SHOW WARNINGS statements. This is the same as the number of condition areas in the diagnostics area, and thus the number of conditions that can be inspected by GET DIAGNOSTICS.

  • max_execution_time

    Introduced5.7.8
    Command-Line Format--max_execution_time=#
    System VariableNamemax_execution_time
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0

    The execution timeout for SELECT statements, in milliseconds. If the value is 0, timeouts are not enabled.

    max_execution_time applies as follows:

    • The global max_execution_time value provides the default for the session value for new connections. The session value applies to SELECT executions executed within the session that include no MAX_EXECUTION_TIME(N) optimizer hint or for which N is 0.

    • max_execution_time applies to read-only SELECT statements. Statements that are not read only are those that invoke a stored function that modifies data as a side effect.

    • max_execution_time is ignored for SELECT statements in stored programs.

    This variable was added in MySQL 5.7.8. Previously, it was named max_statement_time.

  • max_heap_table_size

    Command-Line Format--max_heap_table_size=#
    System VariableNamemax_heap_table_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default16777216
    Min Value16384
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default16777216
    Min Value16384
    Max Value1844674407370954752

    This variable sets the maximum size to which user-created MEMORY tables are permitted to grow. The value of the variable is used to calculate MEMORY table MAX_ROWS values. Setting this variable has no effect on any existing MEMORY table, unless the table is re-created with a statement such as CREATE TABLE or altered with ALTER TABLE or TRUNCATE TABLE. A server restart also sets the maximum size of existing MEMORY tables to the global max_heap_table_size value.

    This variable is also used in conjunction with tmp_table_size to limit the size of internal in-memory tables. See Section 9.4.4, “Internal Temporary Table Use in MySQL”.

    max_heap_table_size is not replicated. See Section 18.4.1.23, “Replication and MEMORY Tables”, and Section 18.4.1.38, “Replication and Variables”, for more information.

  • max_insert_delayed_threads

    Deprecated5.6.7
    System VariableNamemax_insert_delayed_threads
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger

    This variable is a synonym for max_delayed_threads.

    This system variable is deprecated (because DELAYED inserts are not supported), and will be removed in a future release.

  • max_join_size

    Command-Line Format--max_join_size=#
    System VariableNamemax_join_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default18446744073709551615
    Min Value1
    Max Value18446744073709551615

    Do not permit statements that probably need to examine more than max_join_size rows (for single-table statements) or row combinations (for multiple-table statements) or that are likely to do more than max_join_size disk seeks. By setting this value, you can catch statements where keys are not used properly and that would probably take a long time. Set it if your users tend to perform joins that lack a WHERE clause, that take a long time, or that return millions of rows.

    Setting this variable to a value other than DEFAULT resets the value of sql_big_selects to 0. If you set the sql_big_selects value again, the max_join_size variable is ignored.

    If a query result is in the query cache, no result size check is performed, because the result has previously been computed and it does not burden the server to send it to the client.

  • max_length_for_sort_data

    Command-Line Format--max_length_for_sort_data=#
    System VariableNamemax_length_for_sort_data
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default1024
    Min Value4
    Max Value8388608

    The cutoff on the size of index values that determines which filesort algorithm to use. See Section 9.2.1.13, “ORDER BY Optimization”.

  • max_points_in_geometry

    Introduced5.7.8
    Command-Line Format--max_points_in_geometry=integer
    System VariableNamemax_points_in_geometry
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default65536
    Min Value3
    Max Value1048576

    The maximum value of the points_per_circle argument to the ST_Buffer_Strategy() function.

  • max_prepared_stmt_count

    Command-Line Format--max_prepared_stmt_count=#
    System VariableNamemax_prepared_stmt_count
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default16382
    Min Value0
    Max Value1048576

    This variable limits the total number of prepared statements in the server. It can be used in environments where there is the potential for denial-of-service attacks based on running the server out of memory by preparing huge numbers of statements. If the value is set lower than the current number of prepared statements, existing statements are not affected and can be used, but no new statements can be prepared until the current number drops below the limit. The default value is 16,382. The permissible range of values is from 0 to 1 million. Setting the value to 0 disables prepared statements.

  • max_relay_log_size

    Command-Line Format--max_relay_log_size=#
    System VariableNamemax_relay_log_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value1073741824

    If a write by a replication slave to its relay log causes the current log file size to exceed the value of this variable, the slave rotates the relay logs (closes the current file and opens the next one). If max_relay_log_size is 0, the server uses max_binlog_size for both the binary log and the relay log. If max_relay_log_size is greater than 0, it constrains the size of the relay log, which enables you to have different sizes for the two logs. You must set max_relay_log_size to between 4096 bytes and 1GB (inclusive), or to 0. The default value is 0. See Section 18.2.2, “Replication Implementation Details”.

  • max_seeks_for_key

    Command-Line Format--max_seeks_for_key=#
    System VariableNamemax_seeks_for_key
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default4294967295
    Min Value1
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default18446744073709551615
    Min Value1
    Max Value18446744073709551615

    Limit the assumed maximum number of seeks when looking up rows based on a key. The MySQL optimizer assumes that no more than this number of key seeks are required when searching for matching rows in a table by scanning an index, regardless of the actual cardinality of the index (see Section 14.7.5.22, “SHOW INDEX Syntax”). By setting this to a low value (say, 100), you can force MySQL to prefer indexes instead of table scans.

  • max_sort_length

    Command-Line Format--max_sort_length=#
    System VariableNamemax_sort_length
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default1024
    Min Value4
    Max Value8388608

    The number of bytes to use when sorting data values. The server uses only the first max_sort_length bytes of each value and ignores the rest. Consequently, values that differ only after the first max_sort_length bytes compare as equal for GROUP BY, ORDER BY, and DISTINCT operations.

    Increasing the value of max_sort_length may require increasing the value of sort_buffer_size as well. For details, see Section 9.2.1.13, “ORDER BY Optimization”

  • max_sp_recursion_depth

    Command-Line Format--max_sp_recursion_depth[=#]
    System VariableNamemax_sp_recursion_depth
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Max Value255

    The number of times that any given stored procedure may be called recursively. The default value for this option is 0, which completely disables recursion in stored procedures. The maximum value is 255.

    Stored procedure recursion increases the demand on thread stack space. If you increase the value of max_sp_recursion_depth, it may be necessary to increase thread stack size by increasing the value of thread_stack at server startup.

  • max_statement_time

    Introduced5.7.4
    Removed5.7.8
    System VariableNamemax_statement_time
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0

    The execution timeout for SELECT statements, in milliseconds. If the value is 0, timeouts are not enabled.

    max_statement_time applies as follows:

    • The global max_statement_time value provides the default for the session value for new connections. The session value applies to SELECT statements executed within the session that include no MAX_STATEMENT_TIME = N option or for which N is 0.

    • max_statement_time applies to read-only SELECT statements. Statements that are not read only are those that invoke a stored function that modifies data as a side effect.

    • max_statement_time is ignored for SELECT statements in stored programs.

    This variable was added in MySQL 5.7.4 and renamed to max_execution_time in MySQL 5.7.8.

  • max_tmp_tables

    This variable is unused. It is deprecated and will be removed in a future MySQL release.

  • max_user_connections

    Command-Line Format--max_user_connections=#
    System VariableNamemax_user_connections
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value4294967295

    The maximum number of simultaneous connections permitted to any given MySQL user account. A value of 0 (the default) means no limit.

    This variable has a global value that can be set at server startup or runtime. It also has a read-only session value that indicates the effective simultaneous-connection limit that applies to the account associated with the current session. The session value is initialized as follows:

    • If the user account has a nonzero MAX_USER_CONNECTIONS resource limit, the session max_user_connections value is set to that limit.

    • Otherwise, the session max_user_connections value is set to the global value.

    Account resource limits are specified using the CREATE USER or ALTER USER statement. See Section 7.3.4, “Setting Account Resource Limits”.

  • max_write_lock_count

    Command-Line Format--max_write_lock_count=#
    System VariableNamemax_write_lock_count
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default4294967295
    Min Value1
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default18446744073709551615
    Min Value1
    Max Value18446744073709551615

    After this many write locks, permit some pending read lock requests to be processed in between.

  • mecab_rc_file

    Introduced5.7.6
    Command-Line Format--mecab_rc_file
    System VariableNamemecab_rc_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name

    The mecab_rc_file option is used when setting up the MeCab full-text parser.

    The mecab_rc_file option defines the path to the mecabrc configuration file, which is the configuration file for MeCab. The option is read-only and can only be set at startup. The mecabrc configuration file is required to initialize MeCab.

    For information about the MeCab full-text parser, see Section 13.9.9, “MeCab Full-Text Parser Plugin”.

    For information about options that can be specified in the MeCab mecabrc configuration file, refer to the MeCab Documentation on the Google Developers site.

  • metadata_locks_cache_size

    Deprecated5.7.4
    System VariableNamemetadata_locks_cache_size
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default1024
    Min Value1
    Max Value1048576

    The size of the metadata locks cache. The server uses this cache to avoid creation and destruction of synchronization objects. This is particularly helpful on systems where such operations are expensive, such as Windows XP.

    In MySQL 5.7.4, metadata locking implementation changes make this variable unnecessary, so it is deprecated and will be removed in a future MySQL release.

  • metadata_locks_hash_instances

    Deprecated5.7.4
    System VariableNamemetadata_locks_hash_instances
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default8
    Min Value1
    Max Value1024

    The set of metadata locks can be partitioned into separate hashes to permit connections accessing different objects to use different locking hashes and reduce contention. The metadata_locks_hash_instances system variable specifies the number of hashes (default 8).

    In MySQL 5.7.4, metadata locking implementation changes make this variable unnecessary, so it is deprecated and will be removed in a future MySQL release.

  • min_examined_row_limit

    Command-Line Format--min-examined-row-limit=#
    System VariableNamemin_examined_row_limit
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default0
    Min Value0
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default0
    Min Value0
    Max Value18446744073709551615

    Queries that examine fewer than this number of rows are not logged to the slow query log.

  • multi_range_count

    Deprecated5.6.7
    Command-Line Format--multi_range_count=#
    System VariableNamemulti_range_count
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default256
    Min Value1
    Max Value4294967295

    This variable has no effect. It is deprecated and will be removed in a future MySQL release.

  • myisam_data_pointer_size

    Command-Line Format--myisam_data_pointer_size=#
    System VariableNamemyisam_data_pointer_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default6
    Min Value2
    Max Value7

    The default pointer size in bytes, to be used by CREATE TABLE for MyISAM tables when no MAX_ROWS option is specified. This variable cannot be less than 2 or larger than 7. The default value is 6. See Section B.5.2.12, “The table is full”.

  • myisam_max_sort_file_size

    Command-Line Format--myisam_max_sort_file_size=#
    System VariableNamemyisam_max_sort_file_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default2147483648
    Permitted Values (64-bit platforms)Typeinteger
    Default9223372036854775807

    The maximum size of the temporary file that MySQL is permitted to use while re-creating a MyISAM index (during REPAIR TABLE, ALTER TABLE, or LOAD DATA INFILE). If the file size would be larger than this value, the index is created using the key cache instead, which is slower. The value is given in bytes.

    If MyISAM index files exceed this size and disk space is available, increasing the value may help performance. The space must be available in the file system containing the directory where the original index file is located.

  • myisam_mmap_size

    Command-Line Format--myisam_mmap_size=#
    System VariableNamemyisam_mmap_size
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted Values (32-bit platforms)Typeinteger
    Default4294967295
    Min Value7
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default18446744073709551615
    Min Value7
    Max Value18446744073709551615

    The maximum amount of memory to use for memory mapping compressed MyISAM files. If many compressed MyISAM tables are used, the value can be decreased to reduce the likelihood of memory-swapping problems.

  • myisam_recover_options

    System VariableNamemyisam_recover_options
    Variable ScopeGlobal
    Dynamic VariableNo

    The value of the --myisam-recover-options option. See Section 6.1.4, “Server Command Options”.

  • myisam_repair_threads

    Command-Line Format--myisam_repair_threads=#
    System VariableNamemyisam_repair_threads
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default1
    Min Value1
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default1
    Min Value1
    Max Value18446744073709551615

    If this value is greater than 1, MyISAM table indexes are created in parallel (each index in its own thread) during the Repair by sorting process. The default value is 1.

    Note

    Multi-threaded repair is still beta-quality code.

  • myisam_sort_buffer_size

    Command-Line Format--myisam_sort_buffer_size=#
    System VariableNamemyisam_sort_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (Windows, 32-bit platforms)Typeinteger
    Default8388608
    Min Value4096
    Max Value4294967295
    Permitted Values (Windows, 64-bit platforms)Typeinteger
    Default8388608
    Min Value4096
    Max Value18446744073709551615
    Permitted Values (Other, 32-bit platforms)Typeinteger
    Default8388608
    Min Value4096
    Max Value4294967295
    Permitted Values (Other, 64-bit platforms)Typeinteger
    Default8388608
    Min Value4096
    Max Value18446744073709551615

    The size of the buffer that is allocated when sorting MyISAM indexes during a REPAIR TABLE or when creating indexes with CREATE INDEX or ALTER TABLE.

    The maximum permissible setting for myisam_sort_buffer_size is 4GB−1. Larger values are permitted for 64-bit platforms.

  • myisam_stats_method

    Command-Line Format--myisam_stats_method=name
    System VariableNamemyisam_stats_method
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    Defaultnulls_unequal
    Valid Valuesnulls_equal
    nulls_unequal
    nulls_ignored

    How the server treats NULL values when collecting statistics about the distribution of index values for MyISAM tables. This variable has three possible values, nulls_equal, nulls_unequal, and nulls_ignored. For nulls_equal, all NULL index values are considered equal and form a single value group that has a size equal to the number of NULL values. For nulls_unequal, NULL values are considered unequal, and each NULL forms a distinct value group of size 1. For nulls_ignored, NULL values are ignored.

    The method that is used for generating table statistics influences how the optimizer chooses indexes for query execution, as described in Section 9.3.7, “InnoDB and MyISAM Index Statistics Collection”.

  • myisam_use_mmap

    Command-Line Format--myisam_use_mmap
    System VariableNamemyisam_use_mmap
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Use memory mapping for reading and writing MyISAM tables.

  • mysql_native_password_proxy_users

    Introduced5.7.7
    Command-Line Format--mysql_native_password_proxy_users=[={OFF|ON}]
    System VariableNamemysql_native_password_proxy_users
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    This variable controls whether the mysql_native_password built-in authentication plugin supports proxy users. It has no effect unless the check_proxy_users system variable is enabled. For information about user proxying, see Section 7.3.9, “Proxy Users”.

    This variable was added in MySQL 5.7.7. Before 5.7.7, mysql_native_password does not support proxy users.

  • named_pipe

    System VariableNamenamed_pipe
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform SpecificWindows
    Permitted Values (Windows)Typeboolean
    DefaultOFF

    (Windows only.) Indicates whether the server supports connections over named pipes.

  • net_buffer_length

    Command-Line Format--net_buffer_length=#
    System VariableNamenet_buffer_length
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default16384
    Min Value1024
    Max Value1048576

    Each client thread is associated with a connection buffer and result buffer. Both begin with a size given by net_buffer_length but are dynamically enlarged up to max_allowed_packet bytes as needed. The result buffer shrinks to net_buffer_length after each SQL statement.

    This variable should not normally be changed, but if you have very little memory, you can set it to the expected length of statements sent by clients. If statements exceed this length, the connection buffer is automatically enlarged. The maximum value to which net_buffer_length can be set is 1MB.

    The session value of this variable is read only.

  • net_read_timeout

    Command-Line Format--net_read_timeout=#
    System VariableNamenet_read_timeout
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default30
    Min Value1

    The number of seconds to wait for more data from a connection before aborting the read. When the server is reading from the client, net_read_timeout is the timeout value controlling when to abort. When the server is writing to the client, net_write_timeout is the timeout value controlling when to abort. See also slave_net_timeout.

  • net_retry_count

    Command-Line Format--net_retry_count=#
    System VariableNamenet_retry_count
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default10
    Min Value1
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default10
    Min Value1
    Max Value18446744073709551615

    If a read or write on a communication port is interrupted, retry this many times before giving up. This value should be set quite high on FreeBSD because internal interrupts are sent to all threads.

  • net_write_timeout

    Command-Line Format--net_write_timeout=#
    System VariableNamenet_write_timeout
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default60
    Min Value1

    The number of seconds to wait for a block to be written to a connection before aborting the write. See also net_read_timeout.

  • new

    Command-Line Format--new
    System VariableNamenew
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Disabled byskip-new
    Permitted ValuesTypeboolean
    DefaultFALSE

    This variable was used in MySQL 4.0 to turn on some 4.1 behaviors, and is retained for backward compatibility. Its value is always OFF.

    In MySQL Cluster, setting this variable to ON makes it possible to employ partitioning types other than KEY or LINEAR KEY with NDB tables. This feature is experimental only, and not supported in production. For additional information, see User-defined partitioning and the NDB storage engine (MySQL Cluster).

  • ngram_token_size

    Introduced5.7.6
    Command-Line Format--ngram_token_size
    System VariableNamengram_token_size
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default2
    Min Value1
    Max Value10

    Defines the n-gram token size for the n-gram full-text parser. The ngram_token_size option is read-only and can only be modified at startup. The default value is 2 (bigram). The maximum value is 10.

    For more information about how to configure this variable, see Section 13.9.8, “ngram Full-Text Parser”.

  • offline_mode

    Introduced5.7.5
    Command-Line Format--offline_mode=val
    System VariableNameoffline_mode
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Whether the server is in offline mode, which has these characteristics:

    • Connected client users who do not have the SUPER privilege are disconnected on the next request, with an appropriate error. Disconnection includes terminating running statements and releasing locks. Such clients also cannot initiate new connections, and receive an appropriate error.

    • Connected client users who have the SUPER privilege are not disconnected, and can initiate new connections to manage the server.

    • Replication slave threads are permitted to keep applying data to the server.

    Only users who have the SUPER privilege can control offline mode. To put a server in offline mode, change the value of the offline_mode system variable from OFF to ON. To resume normal operations, change offline_mode from ON to OFF. In offline mode, clients that are refused access receive an ER_SERVER_OFFLINE_MODE error.

  • old

    Command-Line Format--old
    System VariableNameold
    Variable ScopeGlobal
    Dynamic VariableNo

    old is a compatibility variable. It is disabled by default, but can be enabled at startup to revert the server to behaviors present in older versions.

    When old is enabled, it changes the default scope of index hints to that used prior to MySQL 5.1.17. That is, index hints with no FOR clause apply only to how indexes are used for row retrieval and not to resolution of ORDER BY or GROUP BY clauses. (See Section 9.9.4, “Index Hints”.) Take care about enabling this in a replication setup. With statement-based binary logging, having different modes for the master and slaves might lead to replication errors.

  • old_alter_table

    Command-Line Format--old-alter-table
    System VariableNameold_alter_table
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    When this variable is enabled, the server does not use the optimized method of processing an ALTER TABLE operation. It reverts to using a temporary table, copying over the data, and then renaming the temporary table to the original, as used by MySQL 5.0 and earlier. For more information on the operation of ALTER TABLE, see Section 14.1.8, “ALTER TABLE Syntax”.

  • old_passwords

    Deprecated5.7.6
    System VariableNameold_passwords
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (<= 5.7.4)Typeenumeration
    Default0
    Valid Values0
    1
    2
    Permitted Values (>= 5.7.5)Typeenumeration
    Default0
    Valid Values0
    2
    Note

    This system variable is deprecated as of MySQL 5.7.6 and will be removed in a future MySQL release.

    This variable controls the password hashing method used by the PASSWORD() function. It also influences password hashing performed by CREATE USER and GRANT statements that specify a password using an IDENTIFIED BY clause.

    The following table shows the permitted values of old_passwords, the password hashing method for each value, and which authentication plugins use passwords hashed with each method.

    ValuePassword Hashing MethodAssociated Authentication Plugin
    0MySQL 4.1 native hashingmysql_native_password
    1Pre-4.1 (old) hashingmysql_old_password
    2SHA-256 hashingsha256_password
    Note

    Passwords that use the pre-4.1 hashing method are less secure than passwords that use the native password hashing method and should be avoided. Pre-4.1 passwords are deprecated and support for them is removed in MySQL 5.7.5. Consequently, old_passwords=1, which causes PASSWORD() to generate pre-4.1 password hashes, is not permitted as of 5.7.5. For account upgrade instructions, see Section 7.5.1.3, “Migrating Away from Pre-4.1 Password Hashing and the mysql_old_password Plugin”.

    If old_passwords=1, PASSWORD(str) returns the same value as OLD_PASSWORD(str). The latter function is not affected by the value of old_passwords.

    If you set old_passwords=2, follow the instructions for using the sha256_password plugin at Section 7.5.1.4, “The SHA-256 Authentication Plugin”.

    The server sets the global old_passwords value during startup to be consistent with the password hashing method required by the default authentication plugin. The default plugin is mysql_native_password unless the default_authentication_plugin system variable is set otherwise.

    As of MySQL 5.7.1, when a client successfully connects to the server, the server sets the session old_passwords value appropriately for the account authentication method. For example, if the account uses the sha256_password authentication plugin, the server sets old_passwords=2.

    For additional information about authentication plugins and hashing formats, see Section 7.3.8, “Pluggable Authentication”, and Section 7.1.2.4, “Password Hashing in MySQL”.

  • open_files_limit

    Command-Line Format--open-files-limit=#
    System VariableNameopen_files_limit
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default5000, with possible adjustment
    Min Value0
    Max Valueplatform dependent

    The number of files that the operating system permits mysqld to open. The value of this variable at runtime is the real value permitted by the system and might be different from the value you specify at server startup. The value is 0 on systems where MySQL cannot change the number of open files.

    The effective open_files_limit value is based on the value specified at system startup (if any) and the values of max_connections and table_open_cache, using these formulas:

    1) 10 + max_connections + (table_open_cache * 2)
    2) max_connections * 5
    3) open_files_limit value specified at startup, 5000 if none
    

    The server attempts to obtain the number of file descriptors using the maximum of those three values. If that many descriptors cannot be obtained, the server attempts to obtain as many as the system will permit.

  • optimizer_prune_level

    Command-Line Format--optimizer_prune_level[=#]
    System VariableNameoptimizer_prune_level
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    Default1

    Controls the heuristics applied during query optimization to prune less-promising partial plans from the optimizer search space. A value of 0 disables heuristics so that the optimizer performs an exhaustive search. A value of 1 causes the optimizer to prune plans based on the number of rows retrieved by intermediate plans.

  • optimizer_search_depth

    Command-Line Format--optimizer_search_depth[=#]
    System VariableNameoptimizer_search_depth
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default62
    Min Value0
    Max Value62

    The maximum depth of search performed by the query optimizer. Values larger than the number of relations in a query result in better query plans, but take longer to generate an execution plan for a query. Values smaller than the number of relations in a query return an execution plan quicker, but the resulting plan may be far from being optimal. If set to 0, the system automatically picks a reasonable value.

  • optimizer_switch

    Command-Line Format--optimizer_switch=value
    System VariableNameoptimizer_switch
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (<= 5.7.4)Typeset
    Valid Valuesbatched_key_access={on|off}
    block_nested_loop={on|off}
    engine_condition_pushdown={on|off}
    firstmatch={on|off}
    index_condition_pushdown={on|off}
    index_merge={on|off}
    index_merge_intersection={on|off}
    index_merge_sort_union={on|off}
    index_merge_union={on|off}
    loosescan={on|off}
    materialization={on|off}
    mrr={on|off}
    mrr_cost_based={on|off}
    semijoin={on|off}
    subquery_materialization_cost_based={on|off}
    use_index_extensions={on|off}
    Permitted Values (5.7.5)Typeset
    Valid Valuesbatched_key_access={on|off}
    block_nested_loop={on|off}
    condition_fanout_filter={on|off}
    engine_condition_pushdown={on|off}
    firstmatch={on|off}
    index_condition_pushdown={on|off}
    index_merge={on|off}
    index_merge_intersection={on|off}
    index_merge_sort_union={on|off}
    index_merge_union={on|off}
    loosescan={on|off}
    materialization={on|off}
    mrr={on|off}
    mrr_cost_based={on|off}
    semijoin={on|off}
    subquery_materialization_cost_based={on|off}
    use_index_extensions={on|off}
    Permitted Values (>= 5.7.6, <= 5.7.7)Typeset
    Valid Valuesbatched_key_access={on|off}
    block_nested_loop={on|off}
    condition_fanout_filter={on|off}
    derived_merge={on|off}
    engine_condition_pushdown={on|off}
    firstmatch={on|off}
    index_condition_pushdown={on|off}
    index_merge={on|off}
    index_merge_intersection={on|off}
    index_merge_sort_union={on|off}
    index_merge_union={on|off}
    loosescan={on|off}
    materialization={on|off}
    mrr={on|off}
    mrr_cost_based={on|off}
    semijoin={on|off}
    subquery_materialization_cost_based={on|off}
    use_index_extensions={on|off}
    Permitted Values (>= 5.7.8)Typeset
    Valid Valuesbatched_key_access={on|off}
    block_nested_loop={on|off}
    condition_fanout_filter={on|off}
    derived_merge={on|off}
    duplicateweedout={on|off}
    engine_condition_pushdown={on|off}
    firstmatch={on|off}
    index_condition_pushdown={on|off}
    index_merge={on|off}
    index_merge_intersection={on|off}
    index_merge_sort_union={on|off}
    index_merge_union={on|off}
    loosescan={on|off}
    materialization={on|off}
    mrr={on|off}
    mrr_cost_based={on|off}
    semijoin={on|off}
    subquery_materialization_cost_based={on|off}
    use_index_extensions={on|off}

    The optimizer_switch system variable enables control over optimizer behavior. The value of this variable is a set of flags, each of which has a value of on or off to indicate whether the corresponding optimizer behavior is enabled or disabled. This variable has global and session values and can be changed at runtime. The global default can be set at server startup.

    To see the current set of optimizer flags, select the variable value:

    mysql> SELECT @@optimizer_switch\G
    *************************** 1. row ***************************
    @@optimizer_switch: index_merge=on,index_merge_union=on,
                        index_merge_sort_union=on,
                        index_merge_intersection=on,
                        engine_condition_pushdown=on,
                        index_condition_pushdown=on,
                        mrr=on,mrr_cost_based=on,
                        block_nested_loop=on,batched_key_access=off,
                        materialization=on,semijoin=on,loosescan=on,
                        firstmatch=on,duplicateweedout=on,
                        subquery_materialization_cost_based=on,
                        use_index_extensions=on,
                        condition_fanout_filter=on,derived_merge=on
    

    For more information about the syntax of this variable and the optimizer behaviors that it controls, see Section 9.9.2, “Controlling Switchable Optimizations”.

  • optimizer_trace

    System VariableNameoptimizer_trace
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring

    This variable controls optimizer tracing. For details, see MySQL Internals: Tracing the Optimizer.

  • optimizer_trace_features

    System VariableNameoptimizer_trace_features
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring

    This variable enables or disables selected optimizer tracing features. For details, see MySQL Internals: Tracing the Optimizer.

  • optimizer_trace_limit

    System VariableNameoptimizer_trace_limit
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default1

    The maximum number of optimizer traces to display. For details, see MySQL Internals: Tracing the Optimizer.

  • optimizer_trace_max_mem_size

    System VariableNameoptimizer_trace_max_mem_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default16384

    The maximum cumulative size of stored optimizer traces. For details, see MySQL Internals: Tracing the Optimizer.

  • optimizer_trace_offset

    System VariableNameoptimizer_trace_offset
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default-1

    The offset of optimizer traces to display. For details, see MySQL Internals: Tracing the Optimizer.

  • performance_schema_xxx

    Performance Schema system variables are listed in Section 25.13, “Performance Schema System Variables”. These variables may be used to configure Performance Schema operation.

  • parser_max_mem_size

    Introduced5.7.12
    Command-Line Format--parser_max_mem_size=N
    System VariableNameparser_max_mem_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default4294967295
    Min Value10000000
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default18446744073709551615
    Min Value10000000
    Max Value18446744073709551615

    The maximum amount of memory available to the parser. The default value places no limit on memory available. The value can be reduced to protect against out-of-memory situations caused by parsing long or complex SQL statements.

  • pid_file

    Command-Line Format--pid-file=file_name
    System VariableNamepid_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name

    The path name of the process ID (PID) file. This variable can be set with the --pid-file option.

  • plugin_dir

    Command-Line Format--plugin_dir=dir_name
    System VariableNameplugin_dir
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name
    DefaultBASEDIR/lib/plugin

    The path name of the plugin directory.

    If the plugin directory is writable by the server, it may be possible for a user to write executable code to a file in the directory using SELECT ... INTO DUMPFILE. This can be prevented by making plugin_dir read only to the server or by setting --secure-file-priv to a directory where SELECT writes can be made safely.

  • port

    Command-Line Format--port=#
    System VariableNameport
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default3306
    Min Value0
    Max Value65535

    The number of the port on which the server listens for TCP/IP connections. This variable can be set with the --port option.

  • preload_buffer_size

    Command-Line Format--preload_buffer_size=#
    System VariableNamepreload_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default32768
    Min Value1024
    Max Value1073741824

    The size of the buffer that is allocated when preloading indexes.

  • profiling

    If set to 0 or OFF (the default), statement profiling is disabled. If set to 1 or ON, statement profiling is enabled and the SHOW PROFILE and SHOW PROFILES statements provide access to profiling information. See Section 14.7.5.31, “SHOW PROFILES Syntax”.

    This variable is deprecated and will be removed in a future MySQL release.

  • profiling_history_size

    The number of statements for which to maintain profiling information if profiling is enabled. The default value is 15. The maximum value is 100. Setting the value to 0 effectively disables profiling. See Section 14.7.5.31, “SHOW PROFILES Syntax”.

    This variable is deprecated and will be removed in a future MySQL release.

  • protocol_version

    System VariableNameprotocol_version
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger

    The version of the client/server protocol used by the MySQL server.

  • proxy_user

    System VariableNameproxy_user
    Variable ScopeSession
    Dynamic VariableNo
    Permitted ValuesTypestring

    If the current client is a proxy for another user, this variable is the proxy user account name. Otherwise, this variable is NULL. See Section 7.3.9, “Proxy Users”.

  • pseudo_slave_mode

    System VariableNamepseudo_slave_mode
    Variable ScopeSession
    Dynamic VariableYes
    Permitted ValuesTypeinteger

    This variable is for internal server use.

  • pseudo_thread_id

    System VariableNamepseudo_thread_id
    Variable ScopeSession
    Dynamic VariableYes
    Permitted ValuesTypeinteger

    This variable is for internal server use.

  • query_alloc_block_size

    Command-Line Format--query_alloc_block_size=#
    System VariableNamequery_alloc_block_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (>= 5.7.9)Typeinteger
    Default8192
    Min Value1024
    Max Value4294967295
    Block Size1024
    Permitted Values (32-bit platforms, <= 5.7.8)Typeinteger
    Default8192
    Min Value1024
    Max Value4294967295
    Block Size1024
    Permitted Values (64-bit platforms, <= 5.7.8)Typeinteger
    Default8192
    Min Value1024
    Max Value18446744073709551615
    Block Size1024

    The allocation size of memory blocks that are allocated for objects created during statement parsing and execution. If you have problems with memory fragmentation, it might help to increase this parameter.

  • query_cache_limit

    Command-Line Format--query_cache_limit=#
    System VariableNamequery_cache_limit
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default1048576
    Min Value0
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default1048576
    Min Value0
    Max Value18446744073709551615

    Do not cache results that are larger than this number of bytes. The default value is 1MB.

  • query_cache_min_res_unit

    Command-Line Format--query_cache_min_res_unit=#
    System VariableNamequery_cache_min_res_unit
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default4096
    Min Value512
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default4096
    Min Value512
    Max Value18446744073709551615

    The minimum size (in bytes) for blocks allocated by the query cache. The default value is 4096 (4KB). Tuning information for this variable is given in Section 9.10.3.3, “Query Cache Configuration”.

  • query_cache_size

    Command-Line Format--query_cache_size=#
    System VariableNamequery_cache_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default1048576
    Min Value0
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default1048576
    Min Value0
    Max Value18446744073709551615

    The amount of memory allocated for caching query results. By default, the query cache is disabled. This is achieved using a default value of 1M, with a default for query_cache_type of 0. (To reduce overhead significantly if you set the size to 0, you should also start the server with query_cache_type=0.

    The permissible values are multiples of 1024; other values are rounded down to the nearest multiple. For nonzero values of query_cache_size, that many bytes of memory are allocated even if query_cache_type=0. See Section 9.10.3.3, “Query Cache Configuration”, for more information.

    The query cache needs a minimum size of about 40KB to allocate its structures. (The exact size depends on system architecture.) If you set the value of query_cache_size too small, a warning will occur, as described in Section 9.10.3.3, “Query Cache Configuration”.

  • query_cache_type

    Command-Line Format--query_cache_type=#
    System VariableNamequery_cache_type
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    Default0
    Valid Values0
    1
    2

    Set the query cache type. Setting the GLOBAL value sets the type for all clients that connect thereafter. Individual clients can set the SESSION value to affect their own use of the query cache. Possible values are shown in the following table.

    OptionDescription
    0 or OFFDo not cache results in or retrieve results from the query cache. Note that this does not deallocate the query cache buffer. To do that, you should set query_cache_size to 0.
    1 or ONCache all cacheable query results except for those that begin with SELECT SQL_NO_CACHE.
    2 or DEMANDCache results only for cacheable queries that begin with SELECT SQL_CACHE.

    This variable defaults to OFF.

    If the server is started with query_cache_type set to 0, it does not acquire the query cache mutex at all, which means that the query cache cannot be enabled at runtime and there is reduced overhead in query execution.

  • query_cache_wlock_invalidate

    Command-Line Format--query_cache_wlock_invalidate
    System VariableNamequery_cache_wlock_invalidate
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultFALSE

    Normally, when one client acquires a WRITE lock on a MyISAM table, other clients are not blocked from issuing statements that read from the table if the query results are present in the query cache. Setting this variable to 1 causes acquisition of a WRITE lock for a table to invalidate any queries in the query cache that refer to the table. This forces other clients that attempt to access the table to wait while the lock is in effect.

  • query_prealloc_size

    Command-Line Format--query_prealloc_size=#
    System VariableNamequery_prealloc_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default8192
    Min Value8192
    Max Value4294967295
    Block Size1024
    Permitted Values (64-bit platforms)Typeinteger
    Default8192
    Min Value8192
    Max Value18446744073709551615
    Block Size1024

    The size of the persistent buffer used for statement parsing and execution. This buffer is not freed between statements. If you are running complex queries, a larger query_prealloc_size value might be helpful in improving performance, because it can reduce the need for the server to perform memory allocation during query execution operations.

  • rand_seed1

    The rand_seed1 and rand_seed2 variables exist as session variables only, and can be set but not read. The variables—but not their values—are shown in the output of SHOW VARIABLES.

    The purpose of these variables is to support replication of the RAND() function. For statements that invoke RAND(), the master passes two values to the slave, where they are used to seed the random number generator. The slave uses these values to set the session variables rand_seed1 and rand_seed2 so that RAND() on the slave generates the same value as on the master.

  • rand_seed2

    See the description for rand_seed1.

  • range_alloc_block_size

    Command-Line Format--range_alloc_block_size=#
    System VariableNamerange_alloc_block_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (>= 5.7.9)Typeinteger
    Default4096
    Min Value4096
    Max Value4294967295
    Block Size1024
    Permitted Values (32-bit platforms, <= 5.7.8)Typeinteger
    Default4096
    Min Value4096
    Max Value4294967295
    Block Size1024
    Permitted Values (64-bit platforms, <= 5.7.8)Typeinteger
    Default4096
    Min Value4096
    Max Value18446744073709551615
    Block Size1024
    Permitted Values (64-bit platforms, >= 5.7.8)Typeinteger
    Default4096
    Min Value4096
    Max Value18446744073709547520
    Block Size1024

    The size of blocks that are allocated when doing range optimization.

  • range_optimizer_max_mem_size

    Introduced5.7.9
    Command-Line Format--range_optimizer_max_mem_size=N
    System VariableNamerange_optimizer_max_mem_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (<= 5.7.11)Typeinteger
    Default1536000
    Permitted Values (>= 5.7.12)Typeinteger
    Default8388608

    The limit on memory consumption for the range optimizer. A value of 0 means no limit. If an execution plan considered by the optimizer uses the range access method but the optimizer estimates that the amount of memory needed for this method would exceed the limit, it abandons the plan and considers other plans. For more information, see Section 9.2.1.2.4, “Limiting Memory Use for Range Optimization”.

  • rbr_exec_mode

    Introduced5.7.1
    System VariableNamerbr_exec_mode
    Variable ScopeSession
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultSTRICT
    Valid ValuesIDEMPOTENT
    STRICT

    This variable switches the server between IDEMPOTENT mode and STRICT mode. IDEMPOTENT mode causes suppression of duplicate-key and no-key-found errors. This mode is useful when replaying a row-based binary log on a server that causes conflicts with existing data. mysqlbinlog uses this mode when you set the --idempotent option by writing the following to the output:

    SET SESSION RBR_EXEC_MODE=IDEMPOTENT;
  • read_buffer_size

    Command-Line Format--read_buffer_size=#
    System VariableNameread_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default131072
    Min Value8200
    Max Value2147479552

    Each thread that does a sequential scan for a MyISAM table allocates a buffer of this size (in bytes) for each table it scans. If you do many sequential scans, you might want to increase this value, which defaults to 131072. The value of this variable should be a multiple of 4KB. If it is set to a value that is not a multiple of 4KB, its value will be rounded down to the nearest multiple of 4KB.

    This option is also used in the following context for all storage engines:

    • For caching the indexes in a temporary file (not a temporary table), when sorting rows for ORDER BY.

    • For bulk insert into partitions.

    • For caching results of nested queries.

    and in one other storage engine-specific way: to determine the memory block size for MEMORY tables.

    The maximum permissible setting for read_buffer_size is 2GB.

    For more information about memory use during different operations, see Section 9.12.4.1, “How MySQL Uses Memory”.

  • read_only

    Command-Line Format--read_only
    System VariableNameread_only
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    When the read_only system variable is enabled, the server permits no client updates except from users who have the SUPER privilege. This variable is disabled by default.

    As of MySQL 5.7.8, the server also supports a super_read_only system variable (disabled by default), which has these effects:

    Even with read_only enabled, the server permits these operations:

    Changes to read_only on a master server are not replicated to slave servers. The value can be set on a slave server independent of the setting on the master.

    The following conditions apply to attempts to enable read_only (including implicit attempts resulting from enabling super_read_only):

    • The attempt fails and an error occurs if you have any explicit locks (acquired with LOCK TABLES) or have a pending transaction.

    • The attempt blocks while other clients hold explicit table locks or have pending transactions, until the locks are released and the transactions end. While the attempt to enable read_only is pending, requests by other clients for table locks or to begin transactions also block until read_only has been set.

    • The attempt blocks if there are active transactions that hold metadata locks, until those transactions end.

    • read_only can be enabled while you hold a global read lock (acquired with FLUSH TABLES WITH READ LOCK) because that does not involve table locks.

  • read_rnd_buffer_size

    Command-Line Format--read_rnd_buffer_size=#
    System VariableNameread_rnd_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default262144
    Min Value1
    Max Value2147483647

    This variable is used for reads from MyISAM tables, and, for any storage engine, for Multi-Range Read optimization.

    When reading rows from a MyISAM table in sorted order following a key-sorting operation, the rows are read through this buffer to avoid disk seeks. See Section 9.2.1.13, “ORDER BY Optimization”. Setting the variable to a large value can improve ORDER BY performance by a lot. However, this is a buffer allocated for each client, so you should not set the global variable to a large value. Instead, change the session variable only from within those clients that need to run large queries.

    The maximum permissible setting for read_rnd_buffer_size is 2GB.

    For more information about memory use during different operations, see Section 9.12.4.1, “How MySQL Uses Memory”. For information about Multi-Range Read optimization, see Section 9.2.1.10, “Multi-Range Read Optimization”.

  • relay_log_purge

    Command-Line Format--relay_log_purge
    System VariableNamerelay_log_purge
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultTRUE

    Disables or enables automatic purging of relay log files as soon as they are not needed any more. The default value is 1 (ON).

  • relay_log_space_limit

    Command-Line Format--relay_log_space_limit=#
    System VariableNamerelay_log_space_limit
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted Values (32-bit platforms)Typeinteger
    Default0
    Min Value0
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default0
    Min Value0
    Max Value18446744073709551615

    The maximum amount of space to use for all relay logs.

  • report_host

    Command-Line Format--report-host=host_name
    System VariableNamereport_host
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring

    The value of the --report-host option.

  • report_password

    Command-Line Format--report-password=name
    System VariableNamereport_password
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring

    The value of the --report-password option. Not the same as the password used for the MySQL replication user account.

  • report_port

    Command-Line Format--report-port=#
    System VariableNamereport_port
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default[slave_port]
    Min Value0
    Max Value65535

    The value of the --report-port option.

  • report_user

    Command-Line Format--report-user=name
    System VariableNamereport_user
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring

    The value of the --report-user option. Not the same as the name for the MySQL replication user account.

  • require_secure_transport

    Introduced5.7.8
    Command-Line Format--require_secure_transport[={OFF|ON}]
    System VariableNamerequire_secure_transport
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Whether client connections to the server are required to use some form of secure transport. When this variable is enabled, the server permits only TCP/IP connections that use SSL, or connections that use a socket file (on Unix) or shared memory (on Windows). The server rejects nonsecure connection attempts, which fail with an ER_SECURE_TRANSPORT_REQUIRED error.

    This capability supplements per-account SSL requirements, which take precedence. For exmaple, if an account is defined with REQUIRE SSL, enabling require_secure_transport does not make it possible to use the account to connect using a Unix socket file.

    It is possible for a server to have no secure transports available. For example, a server on Windows supports no secure transports if started without specifying any SSL certificate or key files and with the shared_memory system variable disabled. Under these conditions, attempts to enable require_secure_transport at startup cause the server to write a message to the error log and exit. Attempts to enable the variable at runtime fail with an ER_NO_SECURE_TRANSPORTS_CONFIGURED error.

  • rpl_semi_sync_master_enabled

    System VariableNamerpl_semi_sync_master_enabled
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Controls whether semisynchronous replication is enabled on the master. To enable or disable the plugin, set this variable to ON or OFF (or 1 or 0), respectively. The default is OFF.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_master_timeout

    System VariableNamerpl_semi_sync_master_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default10000

    A value in milliseconds that controls how long the master waits on a commit for acknowledgment from a slave before timing out and reverting to asynchronous replication. The default value is 10000 (10 seconds).

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_master_trace_level

    System VariableNamerpl_semi_sync_master_trace_level
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default32

    The semisynchronous replication debug trace level on the master. Four levels are defined:

    • 1 = general level (for example, time function failures)

    • 16 = detail level (more verbose information)

    • 32 = net wait level (more information about network waits)

    • 64 = function level (information about function entry and exit)

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_master_wait_for_slave_count

    Introduced5.7.3
    System VariableNamerpl_semi_sync_master_wait_for_slave_count
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default1
    Min Value1
    Max Value65535

    The number of slave acknowledgments the master must receive per transaction before proceeding. By default rpl_semi_sync_master_wait_for_slave_count is 1, meaning that semisynchronous replication proceeds after receiving a single slave acknowledgment. Performance is best for small values of this variable.

    For example, if rpl_semi_sync_master_wait_for_slave_count is 2, then 2 slaves must acknowledge receipt of the transaction before the timeout period configured by rpl_semi_sync_master_timeout for semisynchronous replication to proceed. If less slaves acknowledge receipt of the transaction during the timeout period, the master reverts to normal replication.

    Note

    This behavior also depends on rpl_semi_sync_master_wait_no_slave

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_master_wait_no_slave

    System VariableNamerpl_semi_sync_master_wait_no_slave
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultON

    Controls whether the master waits for the timeout period configured by rpl_semi_sync_master_timeout to expire, even if the slave count drops to less than the number of slaves configured by rpl_semi_sync_master_wait_for_slave_count during the timeout period.

    When the value of rpl_semi_sync_master_wait_no_slave is ON (the default), it is permissible for the slave count to drop to less than rpl_semi_sync_master_wait_for_slave_count during the timeout period. As long as enough slaves acknowledge the transaction before the timeout period expires, semisynchronous replication continues.

    When the value of rpl_semi_sync_master_wait_no_slave is OFF, if the slave count drops to less than the number configured in rpl_semi_sync_master_wait_for_slave_count at any time during the timeout period configured by rpl_semi_sync_master_timeout, the master reverts to normal replication.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_master_wait_point

    Introduced5.7.2
    System VariableNamerpl_semi_sync_master_wait_point
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultAFTER_SYNC
    Valid ValuesAFTER_SYNC
    AFTER_COMMIT

    This variable controls the point at which a semisynchronous replication master waits for slave acknowledgment of transaction receipt before returning a status to the client that committed the transaction. These values are permitted:

    • AFTER_SYNC (the default): The master writes each transaction to its binary log and the slave, and syncs the binary log to disk. The master waits for slave acknowledgment of transaction receipt after the sync. Upon receiving acknowledgment, the master commits the transaction to the storage engine and returns a result to the client, which then can proceed.

    • AFTER_COMMIT: The master writes each transaction to its binary log and the slave, syncs the binary log, and commits the transaction to the storage engine. The master waits for slave acknowledgment of transaction receipt after the commit. Upon receiving acknowledgment, the master returns a result to the client, which then can proceed.

    The replication characteristics of these settings differ as follows:

    • With AFTER_SYNC, all clients see the committed transaction at the same time: After it has been acknowledged by the slave and committed to the storage engine on the master. Thus, all clients see the same data on the master.

      In the event of master failure, all transactions committed on the master have been replicated to the slave (saved to its relay log). A crash of the master and failover to the slave is lossless because the slave is up to date.

    • With AFTER_COMMIT, the client issuing the transaction gets a return status only after the server commits to the storage engine and receives slave acknowledgment. After the commit and before slave acknowledgment, other clients can see the committed transaction before the committing client.

      If something goes wrong such that the slave does not process the transaction, then in the event of a master crash and failover to the slave, it is possible that such clients will see a loss of data relative to what they saw on the master.

    This variable is available only if the master-side semisynchronous replication plugin is installed.

    rpl_semi_sync_master_wait_point was added in MySQL 5.7.2. For older versions, semisynchronous master behavior is equivalent to a setting of AFTER_COMMIT.

    This change introduces a version compatibility constraint because it increments the semisynchronous interface version: Servers for MySQL 5.7.2 and up do not work with semisynchronous replication plugins from older versions, nor do servers from older versions work with semisynchronous replication plugins for MySQL 5.7.2 and up.

  • rpl_semi_sync_slave_enabled

    System VariableNamerpl_semi_sync_slave_enabled
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Controls whether semisynchronous replication is enabled on the slave. To enable or disable the plugin, set this variable to ON or OFF (or 1 or 0), respectively. The default is OFF.

    This variable is available only if the slave-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_slave_trace_level

    System VariableNamerpl_semi_sync_slave_trace_level
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default32

    The semisynchronous replication debug trace level on the slave. See rpl_semi_sync_master_trace_level for the permissible values.

    This variable is available only if the slave-side semisynchronous replication plugin is installed.

  • secure_auth

    Deprecated5.7.5
    Command-Line Format--secure-auth
    System VariableNamesecure_auth
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (<= 5.7.4)Typeboolean
    DefaultON
    Valid ValuesOFF
    ON
    Permitted Values (>= 5.7.5)Typeboolean
    DefaultON
    Valid ValuesON

    If this variable is enabled, the server blocks connections by clients that attempt to use accounts that have passwords stored in the old (pre-4.1) format.

    Enable this variable to prevent all use of passwords employing the old format (and hence insecure communication over the network).

    As of MySQL 5.7.5, this variable is deprecated and will be removed in a future MySQL release. It is always enabled and attempting to disable it produces an error. Before MySQL 5.7.5, this variable is enabled by default but can be disabled.

    Server startup fails with an error if this variable is enabled and the privilege tables are in pre-4.1 format. See Section B.5.2.4, “Client does not support authentication protocol”.

    Note

    Passwords that use the pre-4.1 hashing method are less secure than passwords that use the native password hashing method and should be avoided. Pre-4.1 passwords are deprecated and support for them is removed in MySQL 5.7.5. For account upgrade instructions, see Section 7.5.1.3, “Migrating Away from Pre-4.1 Password Hashing and the mysql_old_password Plugin”.

  • secure_file_priv

    Command-Line Format--secure-file-priv=dir_name
    System VariableNamesecure_file_priv
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted Values (<= 5.7.5)Typestring
    Defaultempty
    Valid Valuesempty
    dirname
    Permitted Values (>= 5.7.6)Typestring
    Defaultplatform specific
    Valid Valuesempty
    dirname
    NULL

    This variable is used to limit the effect of data import and export operations, such as those performed by the LOAD DATA and SELECT ... INTO OUTFILE statements and the LOAD_FILE() function. These operations are permitted only to users who have the FILE privilege.

    secure_file_priv may be set as follows:

    • If empty, the variable has no effect. This is not a secure setting.

    • If set to the name of a directory, the server limits import and export operations to work only with files in that directory. The directory must exist; the server will not create it.

    • If set to NULL, the server disables import and export operations. This value is permitted as of MySQL 5.7.6.

    Before MySQL 5.7.6, this variable is empty by default. As of 5.7.6, the default value is platform specific and depends on the value of the INSTALL_LAYOUT CMake option, as shown in the following table. To specify the default secure_file_priv value explicitly if you are building from source, use the INSTALL_SECURE_FILE_PRIVDIR CMake option.

    INSTALL_LAYOUT ValueDefault secure_file_priv Value
    STANDALONE, WINNULL (>= MySQL 5.7.16), empty (< MySQL 5.7.16)
    DEB, RPM, SLES, SVR4/var/lib/mysql-files
    Otherwisemysql-files under the CMAKE_INSTALL_PREFIX value

    As of MySQL 5.7.8, to set the default secure_file_priv value for the libmysqld embedded server, use the INSTALL_SECURE_FILE_PRIV_EMBEDDEDDIR CMake option. The default value for this option is NULL.

    As of MySQL 5.7.6, the server checks the value of secure_file_priv at startup and writes a warning to the error log if the value is insecure. A non-NULL value is considered insecure if it is empty, or the value is the data directory or a subdirectory of it, or a directory that is accessible by all users. If secure_file_priv is set to a nonexistent path, the server writes an error message to the error log and exits.

  • server_id

    Command-Line Format--server-id=#
    System VariableNameserver_id
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value4294967295

    The server ID, used in replication to give each master and slave a unique identity. This variable is set by the --server-id option. For each server participating in replication, you should pick a positive integer in the range from 1 to 232 − 1 to act as that server's ID.

  • session_track_gtids

    Introduced5.7.6
    Command-Line Format--session_track_gtids=[value]
    System VariableNamesession_track_gtids
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultOFF
    Valid ValuesOFF
    OWN_GTID
    ALL_GTIDS

    Controls a tracker for capturing GTIDs and returning them in the OK packet. Depending on the value of this option, at the end of executing a transaction, the GTIDs specified are captured by the tracker and appended to the OK packet. The possible sets of GTIDs to track are:

    • OFF means that no GTIDs are included in the OK packet. This is the same behavior as versions of MySQL prior to 5.7.6.

    • OWN_GTID configures the tracker to collect GTIDs generated by successfully committed read/write transactions.

    • ALL_GTIDS configures the tracker to collect all of the GTIDs in gtid_executed at the time the current transaction commits, regardless of whether the transaction is read/write or read-only.

    For information about obtaining session state-change information within client programs, see Section 27.8.7.65, “mysql_session_track_get_first()”.

  • session_track_schema

    Introduced5.7.4
    Command-Line Format--session_track_schema=#
    System VariableNamesession_track_schema
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultON

    Controls whether the server tracks changes to the default schema (database) name within the current session and makes this information available to the client when changes occur.

    If notification is enabled, any setting of the default schema is reported, even if the new schema name is the same as the old.

    For information about obtaining session state-change information within client programs, see Section 27.8.7.65, “mysql_session_track_get_first()”.

  • session_track_state_change

    Introduced5.7.4
    Command-Line Format--session_track_state_change=#
    System VariableNamesession_track_state_change
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Controls whether the server tracks changes to the state of the current session and notifies the client when state changes occur. Session state consists of these values:

    • The default schema (database)

    • Session-specific values for system variables

    • User-defined variables

    • Temporary tables

    • Prepared statements

    If the session-state tracker is enabled, any assignments to session state values are reported, even if the new values are the same as the old.

    The session_track_state_change variable controls only notification of when changes occur, not what the changes are. To receive notification for changes to the default schema name and session system variable values, use the session_track_schema and session_track_system_variables system variables.

    For information about obtaining session state-change information within client programs, see Section 27.8.7.65, “mysql_session_track_get_first()”.

  • session_track_system_variables

    Introduced5.7.4
    Command-Line Format--session_track_system_variables=#
    System VariableNamesession_track_system_variables
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring
    Defaulttime_zone, autocommit, character_set_client, character_set_results, character_set_connection

    Controls whether the server tracks changes to the session system variables and makes this information available to the client when changes occur. The variable value is a comma-separated list of variables for which to track changes. By default, notification is enabled for time_zone, autocommit, character_set_client, character_set_results, and character_set_connection. (The latter three variables are those affected by SET NAMES.)

    The special value * causes the server to track changes to all session variables. If given, this value must be specified by itself without specific system variable names.

    Notification occurs for all assignments to tracked session system variables, even if the new values are the same as the old.

    For information about obtaining session state-change information within client programs, see Section 27.8.7.65, “mysql_session_track_get_first()”.

  • sha256_password_auto_generate_rsa_keys

    Introduced5.7.5
    Command-Line Format--sha256_password_auto_generate_rsa_keys[={OFF|ON}]
    System VariableNamesha256_password_auto_generate_rsa_keys
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultON

    This variable is available if the server was compiled using OpenSSL (see Section 7.4.1, “OpenSSL Versus yaSSL”). It controls whether the server autogenerates RSA private/public key-pair files in the data directory, if they do not already exist.

    At startup, the server automatically generates RSA private/public key-pair files in the data directory if the sha256_password_auto_generate_rsa_keys system variable is enabled, no RSA options are specified, and the RSA files are missing from the data directory. These files enable secure password exchange using RSA over unencrypted connections for accounts authenticated by the sha256_password plugin; see Section 7.5.1.4, “The SHA-256 Authentication Plugin”.

    For more information about RSA file autogeneration, including file names and characteristics, see Section 7.4.6.1, “Creating SSL and RSA Certificates and Keys using MySQL”

    The auto_generate_certs system variable is related but controls autogeneration of SSL certificate and key files needed for secure connections using SSL.

  • sha256_password_private_key_path

    System VariableNamesha256_password_private_key_path
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name
    Defaultprivate_key.pem

    This variable is available if MySQL was compiled using OpenSSL (see Section 7.4.1, “OpenSSL Versus yaSSL”). Its value is the path name of the RSA private key file for the sha256_password authentication plugin. If the file is named as a relative path, it is interpreted relative to the server data directory. The file must be in PEM format. Because this file stores a private key, its access mode should be restricted so that only the MySQL server can read it.

    For information about sha256_password, including instructions for creating the RSA key files, see Section 7.5.1.4, “The SHA-256 Authentication Plugin”.

  • sha256_password_proxy_users

    Introduced5.7.7
    Command-Line Format--sha256_password_proxy_users=[={OFF|ON}]
    System VariableNamesha256_password_proxy_users
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    This variable controls whether the sha256_password built-in authentication plugin supports proxy users. It has no effect unless the check_proxy_users system variable is enabled. For information about user proxying, see Section 7.3.9, “Proxy Users”.

    This variable was added in MySQL 5.7.7. Before 5.7.7, sha256_password does not support proxy users.

  • sha256_password_public_key_path

    System VariableNamesha256_password_public_key_path
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name
    Defaultpublic_key.pem

    This variable is available if MySQL was compiled using OpenSSL (see Section 7.4.1, “OpenSSL Versus yaSSL”). Its value is the path name of the RSA public key file for the sha256_password authentication plugin. If the file is named as a relative path, it is interpreted relative to the server data directory. The file must be in PEM format. Because this file stores a public key, copies can be freely distributed to client users. (Clients that explicitly specify a public key when connecting to the server using RSA password encryption must use the same public key as that used by the server.)

    For information about sha256_password, including instructions for creating the RSA key files and how clients specify the RSA public key, see Section 7.5.1.4, “The SHA-256 Authentication Plugin”.

  • shared_memory

    Command-Line Format--shared_memory[={0,1}]
    System VariableNameshared_memory
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform SpecificWindows
    Permitted ValuesTypeboolean
    DefaultFALSE

    (Windows only.) Whether the server permits shared-memory connections.

  • shared_memory_base_name

    Command-Line Format--shared_memory_base_name=name
    System VariableNameshared_memory_base_name
    Variable ScopeGlobal
    Dynamic VariableNo
    Platform SpecificWindows
    Permitted ValuesTypestring
    DefaultMYSQL

    (Windows only.) The name of shared memory to use for shared-memory connections. This is useful when running multiple MySQL instances on a single physical machine. The default name is MYSQL. The name is case sensitive.

  • show_compatibility_56

    Introduced5.7.6
    Deprecated5.7.6
    Command-Line Format--show_compatibility_56[={OFF|ON}]
    System VariableNameshow_compatibility_56
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (<= 5.7.7)Typeboolean
    DefaultON
    Permitted Values (>= 5.7.8)Typeboolean
    DefaultOFF

    The INFORMATION_SCHEMA has tables that contain system and status variable information (see Section 24.10, “The INFORMATION_SCHEMA GLOBAL_VARIABLES and SESSION_VARIABLES Tables”, and Section 24.9, “The INFORMATION_SCHEMA GLOBAL_STATUS and SESSION_STATUS Tables”). As of MySQL 5.7.6, the Performance Schema also contains system and status variable tables (see Section 25.10.13, “Performance Schema System Variable Tables”, and Section 25.10.14, “Performance Schema Status Variable Tables”). The Performance Schema tables are intended to replace the INFORMATION_SCHEMA tables, which are deprecated as of MySQL 5.7.6 and will be removed in a future MySQL release.

    For advice on migrating away from the INFORMATION_SCHEMA tables to the Performance Schema tables, see Section 25.18, “Migrating to Performance Schema System and Status Variable Tables”. To assist in the migration, you can use the show_compatibility_56 system variable, which affects whether MySQL 5.6 compatibility is enabled with respect to how system and status variable information is provided by the INFORMATION_SCHEMA and Performance Schema tables, and also by the SHOW VARIABLES and SHOW STATUS statements.

    Note

    show_compatibility_56 is deprecated because its only purpose is to permit control over deprecated system and status variable information sources that will be removed in a future MySQL release. When those sources are removed, show_compatibility_56 will have no purpose and will be removed as well.

    The following discussion describes the effects of show_compatibility_56:

    For better understanding, it is strongly recommended that you also read these sections:

    Overview of show_compatibility_56 Effects

    The show_compatibility_56 system variable affects these aspects of server operation regarding system and status variables:

    • Information available from the SHOW VARIABLES and SHOW STATUS statements

    • Information available from the INFORMATION_SCHEMA tables that provide system and status variable information

    • Information available from the Performance Schema tables that provide system and status variable information

    • The effect of the FLUSH STATUS statement on status variables

    This list summarizes the effects of show_compatibility_56, with additional details given later:

    • When show_compatibility_56 is ON, compatibility with MySQL 5.6 is enabled. Older variable information sources (SHOW statements, INFORMATION_SCHEMA tables) produce the same output as in MySQL 5.6.

    • When show_compatibility_56 is OFF, compatibility with MySQL 5.6 is disabled. Selecting from the INFORMATION_SCHEMA tables produces an error because the Performance Schema tables are intended to replace them. The INFORMATION_SCHEMA tables are deprecated as of MySQL 5.7.6 and will be removed in a future MySQL release.

      To obtain system and status variable information When show_compatibility_56=OFF, use the Performance Schema tables or the SHOW statements.

      Note

      When show_compatibility_56=OFF, the SHOW VARIABLES and SHOW STATUS statements display rows from the Performance Schema global_variables, session_variables, global_status, and session_status tables.

      As of MySQL 5.7.9, those tables are world readable and accessible without the SELECT privilege, which means that SELECT is not needed to use the SHOW statements, either. Before MySQL 5.7.9, the SELECT privilege is required to access those Performance Schema tables, either directly, or indirectly through the SHOW statements.

    • Several Slave_xxx status variables are available from SHOW STATUS when show_compatibility_56 is ON. When show_compatibility_56 is OFF, some of those variables are not exposed to SHOW STATUS. The information they provide is available in replication-related Performance Schema tables, as described later.

    • show_compatibility_56 has no effect on system variable access using @@ notation: @@GLOBAL.var_name, @@SESSION.var_name, @@var_name.

    • show_compatibility_56 has no effect for the embedded server, which produces 5.6-compatible output in all cases.

    The following descriptions detail the effect of setting show_compatibility_56 to ON or OFF in the contexts in which this variable applies.

    Effect of show_compatibility_56 on SHOW Statements

    SHOW GLOBAL VARIABLES statement:

    • ON: MySQL 5.6 output.

    • OFF: Output displays rows from the Performance Schema global_variables table.

    SHOW [SESSION | LOCAL] VARIABLES statement:

    • ON: MySQL 5.6 output.

    • OFF: Output displays rows from the Performance Schema session_variables table. (In MySQL 5.7.6 and 5.7.7, OFF output does not fully reflect all system variable values in effect for the current session; it includes no rows for global variables that have no session counterpart. This is corrected in MySQL 5.7.8.)

    SHOW GLOBAL STATUS statement:

    • ON: MySQL 5.6 output.

    • OFF: Output displays rows from the Performance Schema global_status table, plus the Com_xxx statement execution counters.

      OFF output includes no rows for session variables that have no global counterpart, unlike ON output.

    SHOW [SESSION | LOCAL] STATUS statement:

    • ON: MySQL 5.6 output.

    • OFF: Output displays rows from the Performance Schema session_status table, plus the Com_xxx statement execution counters. (In MySQL 5.7.6 and 5.7.7, OFF output does not fully reflect all status variable values in effect for the current session; it includes no rows for global variables that have no session counterpart. This is corrected in MySQL 5.7.8.)

    In MySQL 5.7.6 and 5.7.7, for each of the SHOW statements just described, use of a WHERE clause produces a warning when show_compatibility_56=ON and an error when show_compatibility_56=OFF. (This applies to WHERE clauses that are not optimized away. For example, WHERE 1 is trivially true, is optimized away, and thus produces no warning or error.) This behavior does not occur as of MySQL 5.7.8; WHERE is supported as before 5.7.6.

    Effect of show_compatibility_56 on INFORMATION_SCHEMA Tables

    INFORMATION_SCHEMA tables (GLOBAL_VARIABLES, SESSION_VARIABLES, GLOBAL_STATUS, and SESSION_STATUS):

    • ON: MySQL 5.6 output, with a deprecation warning.

    • OFF: Selecting from these tables produces an error. (Before 5.7.9, selecting from these tables produces no output, with a deprecation warning.)

    Effect of show_compatibility_56 on Performance Schema Tables

    Performance Schema system variable tables:

    • OFF:

      • global_variables: Global system variables only.

      • session_variables: System variables in effect for the current session: A row for each session variable, and a row for each global variable that has no session counterpart. (In MySQL 5.7.6 and 5.7.7, the table does not fully reflect all system variable values in effect for the current session; it includes no rows for global variables that have no session counterpart. This is corrected in MySQL 5.7.8.)

      • variables_by_thread: Session system variables only, for each active session.

    • ON: Same output as for OFF. (Before 5.7.8, these tables produce no output.)

    Performance Schema status variable tables:

    • OFF:

      • global_status: Global status variables only.

      • session_status: Status variables in effect the current session: A row for each session variable, and a row for each global variable that has no session counterpart. (In MySQL 5.7.6 and 5.7.7, the table does not fully reflect all status variable values in effect for the current session; it includes no rows for global variables that have no session counterpart. This is corrected in MySQL 5.7.8.)

      • status_by_account Session status variables only, aggregated per account.

      • status_by_host: Session status variables only, aggregated per host name.

      • status_by_thread: Session status variables only, for each active session.

      • status_by_user: Session status variables only, aggregated per user name.

    • ON: Same output as for OFF. (Before 5.7.9, these tables produce no output.)

    Effect of show_compatibility_56 on Slave Status Variables

    Slave status variables:

    Effect of show_compatibility_56 on FLUSH STATUS

    FLUSH STATUS statement:

    • ON: This statement produces MySQL 5.6 behavior. It adds the current thread's session status variable values to the global values and resets the session values to zero. Some global variables may be reset to zero as well. It also resets the counters for key caches (default and named) to zero and sets Max_used_connections to the current number of open connections.

    • OFF: This statement adds the session status from all active sessions to the global status variables, resets the status of all active sessions, and resets account, host, and user status values aggregated from disconnected sessions.

  • show_old_temporals

    Introduced5.7.6
    Deprecated5.7.6
    Command-Line Format--show_old_temporals={OFF|ON}
    System VariableNameshow_old_temporals
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Whether SHOW CREATE TABLE output includes comments to flag temporal columns found to be in pre-5.6.4 format (TIME, DATETIME, and TIMESTAMP columns without support for fractional seconds precision). This variable is disabled by default. If enabled, SHOW CREATE TABLE output looks like this:

    CREATE TABLE `mytbl` (
      `ts` timestamp /* 5.5 binary format */ NOT NULL DEFAULT CURRENT_TIMESTAMP,
      `dt` datetime /* 5.5 binary format */ DEFAULT NULL,
      `t` time /* 5.5 binary format */ DEFAULT NULL
    ) DEFAULT CHARSET=latin1
    

    Output for the COLUMN_TYPE column of the INFORMATION_SCHEMA.COLUMNS table is affected similarly.

    This variable is deprecated and will be removed in a future MySQL release.

  • skip_external_locking

    Command-Line Format--skip-external-locking
    System VariableNameskip_external_locking
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultON

    This is OFF if mysqld uses external locking (system locking), ON if external locking is disabled. This affects only MyISAM table access.

    This variable is set by the --external-locking or --skip-external-locking option. External locking is disabled by default.

    External locking affects only MyISAM table access. For more information, including conditions under which it can and cannot be used, see Section 9.11.5, “External Locking”.

  • skip_name_resolve

    Command-Line Format--skip-name-resolve
    System VariableNameskip_name_resolve
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultOFF

    This variable is set from the value of the --skip-name-resolve option. If it is OFF, mysqld resolves host names when checking client connections. If it is ON, mysqld uses only IP numbers; in this case, all Host column values in the grant tables must be IP addresses or localhost. See Section 9.12.5.2, “DNS Lookup Optimization and the Host Cache”.

  • skip_networking

    Command-Line Format--skip-networking
    System VariableNameskip_networking
    Variable ScopeGlobal
    Dynamic VariableNo

    This is ON if the server permits only local (non-TCP/IP) connections. On Unix, local connections use a Unix socket file. On Windows, local connections use a named pipe or shared memory. This variable can be set to ON with the --skip-networking option.

  • skip_show_database

    Command-Line Format--skip-show-database
    System VariableNameskip_show_database
    Variable ScopeGlobal
    Dynamic VariableNo

    This prevents people from using the SHOW DATABASES statement if they do not have the SHOW DATABASES privilege. This can improve security if you have concerns about users being able to see databases belonging to other users. Its effect depends on the SHOW DATABASES privilege: If the variable value is ON, the SHOW DATABASES statement is permitted only to users who have the SHOW DATABASES privilege, and the statement displays all database names. If the value is OFF, SHOW DATABASES is permitted to all users, but displays the names of only those databases for which the user has the SHOW DATABASES or other privilege. (Note that any global privilege is considered a privilege for the database.)

  • slow_launch_time

    Command-Line Format--slow_launch_time=#
    System VariableNameslow_launch_time
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default2

    If creating a thread takes longer than this many seconds, the server increments the Slow_launch_threads status variable.

  • slow_query_log

    Command-Line Format--slow-query-log
    System VariableNameslow_query_log
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Whether the slow query log is enabled. The value can be 0 (or OFF) to disable the log or 1 (or ON) to enable the log. The default value depends on whether the --slow_query_log option is given. The destination for log output is controlled by the log_output system variable; if that value is NONE, no log entries are written even if the log is enabled.

    Slow is determined by the value of the long_query_time variable. See Section 6.4.5, “The Slow Query Log”.

  • slow_query_log_file

    Command-Line Format--slow-query-log-file=file_name
    System VariableNameslow_query_log_file
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypefile name
    Defaulthost_name-slow.log

    The name of the slow query log file. The default value is host_name-slow.log, but the initial value can be changed with the --slow_query_log_file option.

  • socket

    Command-Line Format--socket={file_name|pipe_name}
    System VariableNamesocket
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring
    Default/tmp/mysql.sock

    On Unix platforms, this variable is the name of the socket file that is used for local client connections. The default is /tmp/mysql.sock. (For some distribution formats, the directory might be different, such as /var/lib/mysql for RPMs.)

    On Windows, this variable is the name of the named pipe that is used for local client connections. The default value is MySQL (not case sensitive).

  • sort_buffer_size

    Command-Line Format--sort_buffer_size=#
    System VariableNamesort_buffer_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (Windows)Typeinteger
    Default262144
    Min Value32768
    Max Value4294967295
    Permitted Values (Other, 32-bit platforms)Typeinteger
    Default262144
    Min Value32768
    Max Value4294967295
    Permitted Values (Other, 64-bit platforms)Typeinteger
    Default262144
    Min Value32768
    Max Value18446744073709551615

    Each session that must perform a sort allocates a buffer of this size. sort_buffer_size is not specific to any storage engine and applies in a general manner for optimization. At minimum the sort_buffer_size value must be large enough to accommodate fifteen tuples in the sort buffer. Also, increasing the value of max_sort_length may require increasing the value of sort_buffer_size. For more information, see Section 9.2.1.13, “ORDER BY Optimization”

    If you see many Sort_merge_passes per second in SHOW GLOBAL STATUS output, you can consider increasing the sort_buffer_size value to speed up ORDER BY or GROUP BY operations that cannot be improved with query optimization or improved indexing.

    The optimizer tries to work out how much space is needed but can allocate more, up to the limit. Setting it larger than required globally will slow down most queries that sort. It is best to increase it as a session setting, and only for the sessions that need a larger size. On Linux, there are thresholds of 256KB and 2MB where larger values may significantly slow down memory allocation, so you should consider staying below one of those values. Experiment to find the best value for your workload. See Section B.5.3.5, “Where MySQL Stores Temporary Files”.

    The maximum permissible setting for sort_buffer_size is 4GB−1. Larger values are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB−1 with a warning).

  • sql_auto_is_null

    System VariableNamesql_auto_is_null
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    Default0

    If this variable is set to 1, then after a statement that successfully inserts an automatically generated AUTO_INCREMENT value, you can find that value by issuing a statement of the following form:

    SELECT * FROM tbl_name WHERE auto_col IS NULL
    

    If the statement returns a row, the value returned is the same as if you invoked the LAST_INSERT_ID() function. For details, including the return value after a multiple-row insert, see Section 13.14, “Information Functions”. If no AUTO_INCREMENT value was successfully inserted, the SELECT statement returns no row.

    The behavior of retrieving an AUTO_INCREMENT value by using an IS NULL comparison is used by some ODBC programs, such as Access. See Obtaining Auto-Increment Values. This behavior can be disabled by setting sql_auto_is_null to 0.

    The default value of sql_auto_is_null is 0.

  • sql_big_selects

    System VariableNamesql_big_selects
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    Default1

    If set to 0, MySQL aborts SELECT statements that are likely to take a very long time to execute (that is, statements for which the optimizer estimates that the number of examined rows exceeds the value of max_join_size). This is useful when an inadvisable WHERE statement has been issued. The default value for a new connection is 1, which permits all SELECT statements.

    If you set the max_join_size system variable to a value other than DEFAULT, sql_big_selects is set to 0.

  • sql_buffer_result

    System VariableNamesql_buffer_result
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    Default0

    If set to 1, sql_buffer_result forces results from SELECT statements to be put into temporary tables. This helps MySQL free the table locks early and can be beneficial in cases where it takes a long time to send results to the client. The default value is 0.

  • sql_log_bin

    System VariableNamesql_log_bin
    Variable ScopeSession
    Dynamic VariableYes
    Permitted ValuesTypeboolean

    This variable controls whether logging to the binary log is done. The default value is 1 (do logging). To change logging for the current session, change the session value of this variable. The session user must have the SUPER privilege to set this variable.

    Setting this variable to 0 prevents GTIDs from being assigned to transactions in the binary log. If you are using GTIDs for replication, this means that, even when binary logging is later enabled once again, the GTIDs written into the log from this point do not account for any transactions that occurred in the meantime—in effect, those transactions are lost.

    In MySQL 5.7, it is not possible to set @@session.sql_log_bin within a transaction or subquery. (Bug #53437)

  • sql_log_off

    System VariableNamesql_log_off
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    Default0

    This variable controls whether logging to the general query log is done. The default value is 0 (do logging). To change logging for the current session, change the session value of this variable. The session user must have the SUPER privilege to set this option. The default value is 0.

  • sql_mode

    Command-Line Format--sql-mode=name
    System VariableNamesql_mode
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (<= 5.7.4)Typeset
    DefaultNO_ENGINE_SUBSTITUTION
    Valid ValuesALLOW_INVALID_DATES
    ANSI_QUOTES
    ERROR_FOR_DIVISION_BY_ZERO
    HIGH_NOT_PRECEDENCE
    IGNORE_SPACE
    NO_AUTO_CREATE_USER
    NO_AUTO_VALUE_ON_ZERO
    NO_BACKSLASH_ESCAPES
    NO_DIR_IN_CREATE
    NO_ENGINE_SUBSTITUTION
    NO_FIELD_OPTIONS
    NO_KEY_OPTIONS
    NO_TABLE_OPTIONS
    NO_UNSIGNED_SUBTRACTION
    NO_ZERO_DATE
    NO_ZERO_IN_DATE
    ONLY_FULL_GROUP_BY
    PAD_CHAR_TO_FULL_LENGTH
    PIPES_AS_CONCAT
    REAL_AS_FLOAT
    STRICT_ALL_TABLES
    STRICT_TRANS_TABLES
    Permitted Values (>= 5.7.5, <= 5.7.6)Typeset
    DefaultONLY_FULL_GROUP_BY STRICT_TRANS_TABLES NO_ENGINE_SUBSTITUTION
    Valid ValuesALLOW_INVALID_DATES
    ANSI_QUOTES
    ERROR_FOR_DIVISION_BY_ZERO
    HIGH_NOT_PRECEDENCE
    IGNORE_SPACE
    NO_AUTO_CREATE_USER
    NO_AUTO_VALUE_ON_ZERO
    NO_BACKSLASH_ESCAPES
    NO_DIR_IN_CREATE
    NO_ENGINE_SUBSTITUTION
    NO_FIELD_OPTIONS
    NO_KEY_OPTIONS
    NO_TABLE_OPTIONS
    NO_UNSIGNED_SUBTRACTION
    NO_ZERO_DATE
    NO_ZERO_IN_DATE
    ONLY_FULL_GROUP_BY
    PAD_CHAR_TO_FULL_LENGTH
    PIPES_AS_CONCAT
    REAL_AS_FLOAT
    STRICT_ALL_TABLES
    STRICT_TRANS_TABLES
    Permitted Values (5.7.7)Typeset
    DefaultONLY_FULL_GROUP_BY STRICT_TRANS_TABLES NO_AUTO_CREATE_USER NO_ENGINE_SUBSTITUTION
    Valid ValuesALLOW_INVALID_DATES
    ANSI_QUOTES
    ERROR_FOR_DIVISION_BY_ZERO
    HIGH_NOT_PRECEDENCE
    IGNORE_SPACE
    NO_AUTO_CREATE_USER
    NO_AUTO_VALUE_ON_ZERO
    NO_BACKSLASH_ESCAPES
    NO_DIR_IN_CREATE
    NO_ENGINE_SUBSTITUTION
    NO_FIELD_OPTIONS
    NO_KEY_OPTIONS
    NO_TABLE_OPTIONS
    NO_UNSIGNED_SUBTRACTION
    NO_ZERO_DATE
    NO_ZERO_IN_DATE
    ONLY_FULL_GROUP_BY
    PAD_CHAR_TO_FULL_LENGTH
    PIPES_AS_CONCAT
    REAL_AS_FLOAT
    STRICT_ALL_TABLES
    STRICT_TRANS_TABLES
    Permitted Values (>= 5.7.8)Typeset
    DefaultONLY_FULL_GROUP_BY STRICT_TRANS_TABLES NO_ZERO_IN_DATE NO_ZERO_DATE ERROR_FOR_DIVISION_BY_ZERO NO_AUTO_CREATE_USER NO_ENGINE_SUBSTITUTION
    Valid ValuesALLOW_INVALID_DATES
    ANSI_QUOTES
    ERROR_FOR_DIVISION_BY_ZERO
    HIGH_NOT_PRECEDENCE
    IGNORE_SPACE
    NO_AUTO_CREATE_USER
    NO_AUTO_VALUE_ON_ZERO
    NO_BACKSLASH_ESCAPES
    NO_DIR_IN_CREATE
    NO_ENGINE_SUBSTITUTION
    NO_FIELD_OPTIONS
    NO_KEY_OPTIONS
    NO_TABLE_OPTIONS
    NO_UNSIGNED_SUBTRACTION
    NO_ZERO_DATE
    NO_ZERO_IN_DATE
    ONLY_FULL_GROUP_BY
    PAD_CHAR_TO_FULL_LENGTH
    PIPES_AS_CONCAT
    REAL_AS_FLOAT
    STRICT_ALL_TABLES
    STRICT_TRANS_TABLES

    The current server SQL mode, which can be set dynamically. For details, see Section 6.1.8, “Server SQL Modes”.

    Note

    MySQL installation programs may configure the SQL mode during the installation process. For example, mysql_install_db creates a default option file named my.cnf in the base installation directory. This file contains a line that sets the SQL mode; see Section 5.4.2, “mysql_install_db — Initialize MySQL Data Directory”.

    If the SQL mode differs from the default or from what you expect, check for a setting in an option file that the server reads at startup.

  • sql_notes

    If set to 1 (the default), warnings of Note level increment warning_count and the server records them. If set to 0, Note warnings do not increment warning_count and the server does not record them. mysqldump includes output to set this variable to 0 so that reloading the dump file does not produce warnings for events that do not affect the integrity of the reload operation.

  • sql_quote_show_create

    If set to 1 (the default), the server quotes identifiers for SHOW CREATE TABLE and SHOW CREATE DATABASE statements. If set to 0, quoting is disabled. This option is enabled by default so that replication works for identifiers that require quoting. See Section 14.7.5.10, “SHOW CREATE TABLE Syntax”, and Section 14.7.5.6, “SHOW CREATE DATABASE Syntax”.

  • sql_safe_updates

    If set to 1, MySQL aborts UPDATE or DELETE statements that do not use a key in the WHERE clause or a LIMIT clause. (Specifically, UPDATE statements must have a WHERE clause that uses a key or a LIMIT clause, or both. DELETE statements must have both.) This makes it possible to catch UPDATE or DELETE statements where keys are not used properly and that would probably change or delete a large number of rows. The default value is 0.

  • sql_select_limit

    System VariableNamesql_select_limit
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger

    The maximum number of rows to return from SELECT statements. The default value for a new connection is the maximum number of rows that the server permits per table. Typical default values are (232)−1 or (264)−1. If you have changed the limit, the default value can be restored by assigning a value of DEFAULT.

    If a SELECT has a LIMIT clause, the LIMIT takes precedence over the value of sql_select_limit.

  • sql_warnings

    This variable controls whether single-row INSERT statements produce an information string if warnings occur. The default is 0. Set the value to 1 to produce an information string.

  • ssl_ca

    Command-Line Format--ssl-ca=file_name
    System VariableNamessl_ca
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name

    The path to a file with a list of trusted SSL CAs.

  • ssl_capath

    Command-Line Format--ssl-capath=dir_name
    System VariableNamessl_capath
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name

    The path to a directory that contains trusted SSL CA certificates in PEM format.

  • ssl_cert

    Command-Line Format--ssl-cert=file_name
    System VariableNamessl_cert
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name

    The name of the SSL certificate file to use for establishing a secure connection.

  • ssl_cipher

    Command-Line Format--ssl-cipher=name
    System VariableNamessl_cipher
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring

    A list of permissible ciphers to use for SSL encryption.

  • ssl_crl

    Command-Line Format--ssl-crl=file_name
    System VariableNamessl_crl
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name

    The path to a file containing certificate revocation lists in PEM format. Revocation lists work for MySQL distributions compiled using OpenSSL (but not yaSSL). See Section 7.4.1, “OpenSSL Versus yaSSL”.

  • ssl_crlpath

    Command-Line Format--ssl-crlpath=dir_name
    System VariableNamessl_crlpath
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name

    The path to a directory that contains files containing certificate revocation lists in PEM format. Revocation lists work for MySQL distributions compiled using OpenSSL (but not yaSSL). See Section 7.4.1, “OpenSSL Versus yaSSL”.

  • ssl_key

    Command-Line Format--ssl-key=file_name
    System VariableNamessl_key
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name

    The name of the SSL key file to use for establishing a secure connection.

  • storage_engine

    Removed5.7.5
    System VariableNamestorage_engine
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultInnoDB

    This variable is deprecated and was removed in MySQL 5.7.5. Use default_storage_engine instead.

  • stored_program_cache

    Command-Line Format--stored-program-cache=#
    System VariableNamestored_program_cache
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (<= 5.7.5)Typeinteger
    Default256
    Min Value256
    Max Value524288
    Permitted Values (>= 5.7.6)Typeinteger
    Default256
    Min Value16
    Max Value524288

    Sets a soft upper limit for the number of cached stored routines per connection. The value of this variable is specified in terms of the number of stored routines held in each of the two caches maintained by the MySQL Server for, respectively, stored procedures and stored functions.

    Whenever a stored routine is executed this cache size is checked before the first or top-level statement in the routine is parsed; if the number of routines of the same type (stored procedures or stored functions according to which is being executed) exceeds the limit specified by this variable, the corresponding cache is flushed and memory previously allocated for cached objects is freed. This allows the cache to be flushed safely, even when there are dependencies between stored routines.

  • super_read_only

    Introduced5.7.8
    Command-Line Format--super_read_only[={OFF|ON}]
    System VariableNamesuper_read_only
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    If the read_only system variable is enabled, the server permits client updates only from users who have the SUPER privilege. If the super_read_only system variable is also enabled, the server prohibits client updates even from users who have SUPER. See the description of the read_only system variable for a description of read-only mode and information about how read_only and super_read_only interact.

    Changes to super_read_only on a master server are not replicated to slave servers. The value can be set on a slave server independent of the setting on the master.

  • sync_frm

    Deprecated5.7.6
    Command-Line Format--sync-frm
    System VariableNamesync_frm
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultTRUE

    If this variable is set to 1, when any nontemporary table is created its .frm file is synchronized to disk (using fdatasync()). This is slower but safer in case of a crash. The default is 1.

    This variable is deprecated in MySQL 5.7.6 and will be removed in a future version of MySQL (when .frm files become obsolete).

  • system_time_zone

    System VariableNamesystem_time_zone
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring

    The server system time zone. When the server begins executing, it inherits a time zone setting from the machine defaults, possibly modified by the environment of the account used for running the server or the startup script. The value is used to set system_time_zone. Typically the time zone is specified by the TZ environment variable. It also can be specified using the --timezone option of the mysqld_safe script.

    The system_time_zone variable differs from time_zone. Although they might have the same value, the latter variable is used to initialize the time zone for each client that connects. See Section 11.6, “MySQL Server Time Zone Support”.

  • table_definition_cache

    System VariableNametable_definition_cache
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default-1 (autosized)
    Min Value400
    Max Value524288

    The number of table definitions (from .frm files) that can be stored in the definition cache. If you use a large number of tables, you can create a large table definition cache to speed up opening of tables. The table definition cache takes less space and does not use file descriptors, unlike the normal table cache. The minimum value is 400. The default value is based on the following formula, capped to a limit of 2000:

    400 + (table_open_cache / 2)
    

    For InnoDB, table_definition_cache acts as a soft limit for the number of open table instances in the InnoDB data dictionary cache. If the number of open table instances exceeds the table_definition_cache setting, the LRU mechanism begins to mark table instances for eviction and eventually removes them from the data dictionary cache. The limit helps address situations in which significant amounts of memory would be used to cache rarely used table instances until the next server restart. The number of table instances with cached metadata could be higher than the limit defined by table_definition_cache, because InnoDB system table instances and parent and child table instances with foreign key relationships are not placed on the LRU list and are not subject to eviction from memory.

    Additionally, table_definition_cache defines a soft limit for the number of InnoDB file-per-table tablespaces that can be open at one time, which is also controlled by innodb_open_files. If both table_definition_cache and innodb_open_files are set, the highest setting is used. If neither variable is set, table_definition_cache, which has a higher default value, is used. If the number of open tablespace file handles exceeds the limit defined by table_definition_cache or innodb_open_files, the LRU mechanism searches the tablespace file LRU list for files that are fully flushed and are not currently being extended. This process is performed each time a new tablespace is opened. If there are no inactive tablespaces, no tablespace files are closed.

  • table_open_cache

    System VariableNametable_open_cache
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default2000
    Min Value1
    Max Value524288

    The number of open tables for all threads. Increasing this value increases the number of file descriptors that mysqld requires. You can check whether you need to increase the table cache by checking the Opened_tables status variable. See Section 6.1.7, “Server Status Variables”. If the value of Opened_tables is large and you do not use FLUSH TABLES often (which just forces all tables to be closed and reopened), then you should increase the value of the table_open_cache variable. For more information about the table cache, see Section 9.4.3.1, “How MySQL Opens and Closes Tables”.

  • table_open_cache_instances

    System VariableNametable_open_cache_instances
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted Values (<= 5.7.7)Typeinteger
    Default1
    Min Value1
    Max Value64
    Permitted Values (>= 5.7.8)Typeinteger
    Default16
    Min Value1
    Max Value64

    The number of open tables cache instances. To improve scalability by reducing contention among sessions, the open tables cache can be partitioned into several smaller cache instances of size table_open_cache / table_open_cache_instances . A session needs to lock only one instance to access it for DML statements. This segments cache access among instances, permitting higher performance for operations that use the cache when there are many sessions accessing tables. (DDL statements still require a lock on the entire cache, but such statements are much less frequent than DML statements.)

    A value of 8 or 16 is recommended on systems that routinely use 16 or more cores.

  • thread_cache_size

    Command-Line Format--thread_cache_size=#
    System VariableNamethread_cache_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default-1 (autosized)
    Min Value0
    Max Value16384

    How many threads the server should cache for reuse. When a client disconnects, the client's threads are put in the cache if there are fewer than thread_cache_size threads there. Requests for threads are satisfied by reusing threads taken from the cache if possible, and only when the cache is empty is a new thread created. This variable can be increased to improve performance if you have a lot of new connections. Normally, this does not provide a notable performance improvement if you have a good thread implementation. However, if your server sees hundreds of connections per second you should normally set thread_cache_size high enough so that most new connections use cached threads. By examining the difference between the Connections and Threads_created status variables, you can see how efficient the thread cache is. For details, see Section 6.1.7, “Server Status Variables”.

    The default value is based on the following formula, capped to a limit of 100:

    8 + (max_connections / 100)
    

    This variable has no effect for the embedded server (libmysqld) and as of MySQL 5.7.2 is no longer visible within the embedded server.

  • thread_concurrency

    Deprecated5.6.1
    Removed5.7.2
    Command-Line Format--thread_concurrency=#
    System VariableNamethread_concurrency
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default10
    Min Value1
    Max Value512

    This variable is specific to Solaris 8 and earlier systems, for which mysqld invokes the thr_setconcurrency() function with the variable value. This function enables applications to give the threads system a hint about the desired number of threads that should be run at the same time. Current Solaris versions document this as having no effect.

    This variable was removed in MySQL 5.7.2.

  • thread_handling

    Command-Line Format--thread_handling=name
    System VariableNamethread_handling
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted Values (<= 5.7.8)Typeenumeration
    Defaultone-thread-per-connection
    Valid Valuesno-threads
    one-thread-per-connection
    Permitted Values (>= 5.7.9)Typeenumeration
    Defaultone-thread-per-connection
    Valid Valuesno-threads
    one-thread-per-connection
    dynamically-loaded

    The thread-handling model used by the server for connection threads. The permissible values are no-threads (the server uses a single thread to handle one connection) and one-thread-per-connection (the server uses one thread to handle each client connection). no-threads is useful for debugging under Linux; see Section 28.5, “Debugging and Porting MySQL”.

    This variable has no effect for the embedded server (libmysqld) and as of MySQL 5.7.2 is no longer visible within the embedded server.

  • thread_pool_algorithm

    Introduced5.7.9
    Command-Line Format--thread_pool_algorithm=#
    System VariableNamethread_pool_algorithm
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value1

    This variable controls which algorithm the thread pool plugin uses:

    • A value of 0 (the default) uses a conservative low-concurrency algorithm which is most well tested and is known to produce very good results.

    • A value of 1 increases the concurrency and uses a more aggressive algorithm which at times has been known to perform 5–10% better on optimal thread counts, but has degrading performance as the number of connections increases. Its use should be considered as experimental and not supported.

      This variable was added in MySQL 5.7.9. It is available only if the thread pool plugin is enabled. See Section 6.5.4, “MySQL Enterprise Thread Pool”

  • thread_pool_high_priority_connection

    Introduced5.7.9
    Command-Line Format--thread_pool_high_priority_connection=#
    System VariableNamethread_pool_high_priority_connection
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value1

    This variable affects queuing of new statements prior to execution. If the value is 0 (false, the default), statement queuing uses both the low-priority and high-priority queues. If the value is 1 (true), queued statements always go to the high-priority queue.

    This variable was added in MySQL 5.7.9. It is available only if the thread pool plugin is enabled. See Section 6.5.4, “MySQL Enterprise Thread Pool”

  • thread_pool_max_unused_threads

    Introduced5.7.9
    Command-Line Format--thread_pool_max_unused_threads=#
    System VariableNamethread_pool_max_unused_threads
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value4096

    The maximum permitted number of unused threads in the thread pool. This variable makes it possible to limit the amount of memory used by sleeping threads.

    A value of 0 (the default) means no limit on the number of sleeping threads. A value of N where N is greater than 0 means 1 consumer thread and N−1 reserve threads. In this case, if a thread is ready to sleep but the number of sleeping threads is already at the maximum, the thread exits rather than going to sleep.

    A sleeping thread is either sleeping as a consumer thread or a reserve thread. The thread pool permits one thread to be the consumer thread when sleeping. If a thread goes to sleep and there is no existing consumer thread, it will sleep as a consumer thread. When a thread must be woken up, a consumer thread is selected if there is one. A reserve thread is selected only when there is no consumer thread to wake up.

    This variable was added in MySQL 5.7.9. It is available only if the thread pool plugin is enabled. See Section 6.5.4, “MySQL Enterprise Thread Pool”

  • thread_pool_prio_kickup_timer

    Introduced5.7.9
    Command-Line Format--thread_pool_prio_kickup_timer=#
    System VariableNamethread_pool_prio_kickup_timer
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default1000
    Min Value0
    Max Value4294967294

    This variable affects statements waiting for execution in the low-priority queue. The value is the number of milliseconds before a waiting statement is moved to the high-priority queue. The default is 1000 (1 second). The range of values is 0 to 232 − 2.

    This variable was added in MySQL 5.7.9. It is available only if the thread pool plugin is enabled. See Section 6.5.4, “MySQL Enterprise Thread Pool”

  • thread_pool_size

    Introduced5.7.9
    Command-Line Format--thread_pool_size=#
    System VariableNamethread_pool_size
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default16
    Min Value1
    Max Value64

    The number of thread groups in the thread pool. This is the most important parameter controlling thread pool performance. It affects how many statements can execute simultaneously. The default value is 16, with a range from 1 to 64 of permissible values. If a value outside this range is specified, the thread pool plugin does not load and the server writes a message to the error log.

    This variable was added in MySQL 5.7.9. It is available only if the thread pool plugin is enabled. See Section 6.5.4, “MySQL Enterprise Thread Pool”

  • thread_pool_stall_limit

    Introduced5.7.9
    Command-Line Format--thread_pool_stall_limit=#
    System VariableNamethread_pool_stall_limit
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default6
    Min Value4
    Max Value600

    This variable affects executing statements. The value is the amount of time a statement has to finish after starting to execute before it becomes defined as stalled, at which point the thread pool permits the thread group to begin executing another statement. The value is measured in 10 millisecond units, so a value of 6 (the default) means 60ms. The range of values is 4 to 600 (40ms to 6s). Short wait values permit threads to start more quickly. Short values are also better for avoiding deadlock situations. Long wait values are useful for workloads that include long-running statements, to avoid starting too many new statements while the current ones execute.

    This variable was added in MySQL 5.7.9. It is available only if the thread pool plugin is enabled. See Section 6.5.4, “MySQL Enterprise Thread Pool”

  • thread_stack

    Command-Line Format--thread_stack=#
    System VariableNamethread_stack
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted Values (32-bit platforms)Typeinteger
    Default196608
    Min Value131072
    Max Value4294967295
    Block Size1024
    Permitted Values (64-bit platforms)Typeinteger
    Default262144
    Min Value131072
    Max Value18446744073709551615
    Block Size1024

    The stack size for each thread. The default of 192KB (256KB for 64-bit systems) is large enough for normal operation. If the thread stack size is too small, it limits the complexity of the SQL statements that the server can handle, the recursion depth of stored procedures, and other memory-consuming actions.

  • time_format

    This variable is unused. It is deprecated and will be removed in a future MySQL release.

  • time_zone

    System VariableNametime_zone
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring

    The current time zone. This variable is used to initialize the time zone for each client that connects. By default, the initial value of this is 'SYSTEM' (which means, use the value of system_time_zone). The value can be specified explicitly at server startup with the --default-time-zone option. See Section 11.6, “MySQL Server Time Zone Support”.

  • timed_mutexes

    Deprecated5.6.20
    Removed5.7.5
    Command-Line Format--timed_mutexes
    System VariableNametimed_mutexes
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    This deprecated variable has no use and was removed in MySQL 5.7.5.

  • timestamp

    System VariableNametimestamp
    Variable ScopeSession
    Dynamic VariableYes
    Permitted ValuesTypenumeric

    Set the time for this client. This is used to get the original timestamp if you use the binary log to restore rows. timestamp_value should be a Unix epoch timestamp (a value like that returned by UNIX_TIMESTAMP(), not a value in 'YYYY-MM-DD hh:mm:ss' format) or DEFAULT.

    Setting timestamp to a constant value causes it to retain that value until it is changed again. Setting timestamp to DEFAULT causes its value to be the current date and time as of the time it is accessed.

    In MySQL 5.7, timestamp is a DOUBLE rather than BIGINT because its value includes a microseconds part.

    SET timestamp affects the value returned by NOW() but not by SYSDATE(). This means that timestamp settings in the binary log have no effect on invocations of SYSDATE(). The server can be started with the --sysdate-is-now option to cause SYSDATE() to be an alias for NOW(), in which case SET timestamp affects both functions.

  • tls_version

    Introduced5.7.10
    Command-Line Format--tls_version=protocol_list
    System VariableNametls_version
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted Values (OpenSSL)Typestring
    DefaultTLSv1,TLSv1.1,TLSv1.2
    Permitted Values (yaSSL)Typestring
    DefaultTLSv1,TLSv1.1

    The protocols permitted by the server for encrypted connections. The value is a comma-separated list containing one or more protocol names. The protocols that can be named for this variable depend on the SSL library used to compile MySQL. For details, see Section 7.4.3, “Secure Connection Protocols and Ciphers”.

  • tmp_table_size

    Command-Line Format--tmp_table_size=#
    System VariableNametmp_table_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default16777216
    Min Value1024
    Max Value18446744073709551615

    The maximum size of internal in-memory temporary tables. This variable does not apply to user-created MEMORY tables.

    The actual limit is determined from whichever of the values of tmp_table_size and max_heap_table_size is smaller. If an in-memory temporary table exceeds the limit, MySQL automatically converts it to an on-disk temporary table. As of MySQL 5.7.5, the internal_tmp_disk_storage_engine option defines the storage engine used for on-disk temporary tables. Prior to MySQL 5.7.5, the MyISAM storage engine is used.

    Increase the value of tmp_table_size (and max_heap_table_size if necessary) if you do many advanced GROUP BY queries and you have lots of memory.

    You can compare the number of internal on-disk temporary tables created to the total number of internal temporary tables created by comparing the values of the Created_tmp_disk_tables and Created_tmp_tables variables.

    See also Section 9.4.4, “Internal Temporary Table Use in MySQL”.

  • tmpdir

    Command-Line Format--tmpdir=dir_name
    System VariableNametmpdir
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name

    The directory used for temporary files and temporary tables. This variable can be set to a list of several paths that are used in round-robin fashion. Paths should be separated by colon characters (:) on Unix and semicolon characters (;) on Windows.

    The multiple-directory feature can be used to spread the load between several physical disks. If the MySQL server is acting as a replication slave, you should not set tmpdir to point to a directory on a memory-based file system or to a directory that is cleared when the server host restarts. A replication slave needs some of its temporary files to survive a machine restart so that it can replicate temporary tables or LOAD DATA INFILE operations. If files in the temporary file directory are lost when the server restarts, replication fails. You can set the slave's temporary directory using the slave_load_tmpdir variable. In that case, the slave will not use the general tmpdir value and you can set tmpdir to a nonpermanent location.

  • transaction_alloc_block_size

    Command-Line Format--transaction_alloc_block_size=#
    System VariableNametransaction_alloc_block_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (>= 5.7.6)Typeinteger
    Default8192
    Min Value1024
    Max Value131072
    Block Size1024
    Permitted Values (32-bit platforms, <= 5.7.5)Typeinteger
    Default8192
    Min Value1024
    Max Value4294967295
    Block Size1024
    Permitted Values (64-bit platforms, <= 5.7.5)Typeinteger
    Default8192
    Min Value1024
    Max Value18446744073709551615
    Block Size1024

    The amount in bytes by which to increase a per-transaction memory pool which needs memory. See the description of transaction_prealloc_size.

  • transaction_prealloc_size

    Command-Line Format--transaction_prealloc_size=#
    System VariableNametransaction_prealloc_size
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (>= 5.7.6)Typeinteger
    Default4096
    Min Value1024
    Max Value131072
    Block Size1024
    Permitted Values (32-bit platforms, <= 5.7.5)Typeinteger
    Default4096
    Min Value1024
    Max Value4294967295
    Block Size1024
    Permitted Values (64-bit platforms, <= 5.7.5)Typeinteger
    Default4096
    Min Value1024
    Max Value18446744073709551615
    Block Size1024

    There is a per-transaction memory pool from which various transaction-related allocations take memory. The initial size of the pool in bytes is transaction_prealloc_size. For every allocation that cannot be satisfied from the pool because it has insufficient memory available, the pool is increased by transaction_alloc_block_size bytes. When the transaction ends, the pool is truncated to transaction_prealloc_size bytes.

    By making transaction_prealloc_size sufficiently large to contain all statements within a single transaction, you can avoid many malloc() calls.

  • transaction_write_set_extraction

    Introduced5.7.6
    Command-Line Format--transaction_write_set_extraction=[value]
    System VariableNametransaction_write_set_extraction
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (<= 5.7.13)Typeenumeration
    DefaultOFF
    Valid ValuesOFF
    MURMUR32
    Permitted Values (>= 5.7.14)Typeenumeration
    DefaultOFF
    Valid ValuesOFF
    MURMUR32
    XXHASH64

    Defines the algorithm used to generate a hash identifying the writes associated with a transaction. If you are using Group Replication, the hash value is used for distributed conflict detection and handling. On 64-bit systems running Group Replication, we recommend setting this to XXHASH64 in order to avoid unnecessary hash collisions which result in certification failures and the roll back of user transactions. See Section 19.7.1, “Group Replication Requirements”.

  • tx_isolation

    System VariableNametx_isolation
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultREPEATABLE-READ
    Valid ValuesREAD-UNCOMMITTED
    READ-COMMITTED
    REPEATABLE-READ
    SERIALIZABLE

    The default transaction isolation level. Defaults to REPEATABLE-READ.

    This variable can be set directly, or indirectly using the SET TRANSACTION statement. See Section 14.3.6, “SET TRANSACTION Syntax”. If you set tx_isolation directly to an isolation level name that contains a space, the name should be enclosed within quotation marks, with the space replaced by a dash. For example:

    SET tx_isolation = 'READ-COMMITTED';
    

    Any unique prefix of a valid value may be used to set the value of this variable.

    The default transaction isolation level can also be set at startup using the --transaction-isolation server option.

  • tx_read_only

    System VariableNametx_read_only
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    The default transaction access mode. The value can be OFF (read/write, the default) or ON (read only).

    This variable can be set directly, or indirectly using the SET TRANSACTION statement. See Section 14.3.6, “SET TRANSACTION Syntax”.

    To set the default transaction access mode at startup, use the --transaction-read-only server option.

  • unique_checks

    System VariableNameunique_checks
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    Default1

    If set to 1 (the default), uniqueness checks for secondary indexes in InnoDB tables are performed. If set to 0, storage engines are permitted to assume that duplicate keys are not present in input data. If you know for certain that your data does not contain uniqueness violations, you can set this to 0 to speed up large table imports to InnoDB.

    Setting this variable to 0 does not require storage engines to ignore duplicate keys. An engine is still permitted to check for them and issue duplicate-key errors if it detects them.

  • updatable_views_with_limit

    Command-Line Format--updatable_views_with_limit=#
    System VariableNameupdatable_views_with_limit
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    Default1

    This variable controls whether updates to a view can be made when the view does not contain all columns of the primary key defined in the underlying table, if the update statement contains a LIMIT clause. (Such updates often are generated by GUI tools.) An update is an UPDATE or DELETE statement. Primary key here means a PRIMARY KEY, or a UNIQUE index in which no column can contain NULL.

    The variable can have two values:

    • 1 or YES: Issue a warning only (not an error message). This is the default value.

    • 0 or NO: Prohibit the update.

  • validate_password_xxx

    The validate_password plugin implements a set of system variables having names of the form validate_password_xxx. These variables affect password testing by that plugin; see Section 7.5.3.2, “Password Validation Plugin Options and Variables”.

  • validate_user_plugins

    System VariableNamevalidate_user_plugins
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultON

    If this variable is enabled (the default), the server checks each user account and produces a warning if conditions are found that would make the account unusable:

    • The account requires an authentication plugin that is not loaded.

    • The account requires the sha256_password authentication plugin but the server was started with neither SSL nor RSA enabled as required by this plugin.

    Enabling validate_user_plugins slows down server initialization and FLUSH PRIVILEGES. If you do not require the additional checking, you can disable this variable at startup to avoid the performance decrement.

  • version

    The version number for the server. The value might also include a suffix indicating server build or configuration information. -log indicates that one or more of the general log, slow query log, or binary log are enabled. -debug indicates that the server was built with debugging support enabled.

  • version_comment

    System VariableNameversion_comment
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring

    The CMake configuration program has a COMPILATION_COMMENT option that permits a comment to be specified when building MySQL. This variable contains the value of that comment. See Section 2.9.4, “MySQL Source-Configuration Options”.

  • version_compile_machine

    System VariableNameversion_compile_machine
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring

    The type of the server binary.

  • version_compile_os

    System VariableNameversion_compile_os
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring

    The type of operating system on which MySQL was built.

  • wait_timeout

    Command-Line Format--wait_timeout=#
    System VariableNamewait_timeout
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (Windows)Typeinteger
    Default28800
    Min Value1
    Max Value2147483
    Permitted Values (Other)Typeinteger
    Default28800
    Min Value1
    Max Value31536000

    The number of seconds the server waits for activity on a noninteractive connection before closing it.

    On thread startup, the session wait_timeout value is initialized from the global wait_timeout value or from the global interactive_timeout value, depending on the type of client (as defined by the CLIENT_INTERACTIVE connect option to mysql_real_connect()). See also interactive_timeout.

  • warning_count

    The number of errors, warnings, and notes that resulted from the last statement that generated messages. This variable is read only. See Section 14.7.5.40, “SHOW WARNINGS Syntax”.

6.1.6 Using System Variables

The MySQL server maintains many system variables that indicate how it is configured. Section 6.1.5, “Server System Variables”, describes the meaning of these variables. Each system variable has a default value. System variables can be set at server startup using options on the command line or in an option file. Most of them can be changed dynamically while the server is running by means of the SET statement, which enables you to modify operation of the server without having to stop and restart it. You can also use system variable values in expressions.

There are two scopes in which system variables exist. Global variables affect the overall operation of the server. Session variables affect its operation for individual client connections. A given system variable can have both a global and a session value. Global and session system variables are related as follows:

  • When the server starts, it initializes each global variable to its default value. These defaults can be changed by options specified on the command line or in an option file. (See Section 5.2.3, “Specifying Program Options”.)

  • The server also maintains a set of session variables for each client that connects. The client's session variables are initialized at connect time using the current values of the corresponding global variables. For example, a client's SQL mode is controlled by the session sql_mode value, which is initialized when the client connects to the value of the global sql_mode value.

    For some system variables, the session value is not initialized from the corresponding global value; if so, that is indicated in the variable description.

System variable values can be set globally at server startup by using options on the command line or in an option file. When you use a startup option to set a variable that takes a numeric value, the value can be given with a suffix of K, M, or G (either uppercase or lowercase) to indicate a multiplier of 1024, 10242 or 10243; that is, units of kilobytes, megabytes, or gigabytes, respectively. Thus, the following command starts the server with a query cache size of 16 megabytes and a maximum packet size of one gigabyte:

mysqld --query_cache_size=16M --max_allowed_packet=1G

Within an option file, those variables are set like this:

[mysqld]
query_cache_size=16M
max_allowed_packet=1G

The lettercase of suffix letters does not matter; 16M and 16m are equivalent, as are 1G and 1g.

To restrict the maximum value to which a system variable can be set at runtime with the SET statement, specify this maximum by using an option of the form --maximum-var_name=value at server startup. For example, to prevent the value of query_cache_size from being increased to more than 32MB at runtime, use the option --maximum-query_cache_size=32M.

Many system variables are dynamic and can be changed at runtime by using the SET statement. For a list, see Section 6.1.6.2, “Dynamic System Variables”. To change a system variable with SET, refer to it by name, optionally preceded by a modifier:

  • To indicate that a variable is a global variable, precede its name by the GLOBAL keyword or the @@global. qualifier:

    SET GLOBAL max_connections = 1000;
    SET @@global.max_connections = 1000;
    

    The SUPER privilege is required to set global variables.

  • To indicate that a variable is a session variable, precede its name by the SESSION keyword or either the @@session. or @@ qualifier:

    SET SESSION sql_mode = 'TRADITIONAL';
    SET @@session.sql_mode = 'TRADITIONAL';
    SET @@sql_mode = 'TRADITIONAL';
    

    Setting a session variable normally requires no special privilege, although there are exceptions that require the SUPER privilege (such as sql_log_bin). A client can change its own session variables, but not those of any other client.

  • LOCAL and @@local. are synonyms for SESSION and @@session..

  • If no modifier is present, SET changes the session variable.

  • An error occurs under these circumstances:

    • Use of SET GLOBAL (or @@global.) when setting a variable that has only a session value:

      mysql> SET GLOBAL sql_log_bin = ON;
      ERROR 1231 (42000): Variable 'sql_log_bin' can't be
      set to the value of 'ON'
      
    • Omission of GLOBAL (or @@global.) when setting a variable that has only a global value:

      mysql> SET max_connections = 1000;
      ERROR 1229 (HY000): Variable 'max_connections' is a
      GLOBAL variable and should be set with SET GLOBAL
      
    • Use of SET SESSION (or @@SESSION.) when setting a variable that has only a global value:

      mysql> SET SESSION max_connections = 1000;
      ERROR 1229 (HY000): Variable 'max_connections' is a
      GLOBAL variable and should be set with SET GLOBAL
      

The preceding modifiers apply only to system variables. An error occurs for attempts to apply them to user-defined variables, stored procedure or function parameters, or stored program local variables.

A SET statement can contain multiple variable assignments, separated by commas. This statement assigns values to a user-defined variable and a system variable:

SET @x = 1, SESSION sql_mode = '';

If you set multiple system variables, the most recent GLOBAL or SESSION modifier in the statement is used for following assignments that have no modifier specified.

Examples of multiple-variable assignment:

SET GLOBAL sort_buffer_size = 1000000, SESSION sort_buffer_size = 1000000;
SET @@global.sort_buffer_size = 1000000, @@local.sort_buffer_size = 1000000;
SET GLOBAL max_connections = 1000, sort_buffer_size = 1000000;

If any variable assignment in a SET statement fails, the entire statement fails and no variables are changed.

If you change a session system variable, the value remains in effect within your session until you change the variable to a different value or the session ends. The change has no effect on other sessions.

If you change a global system variable, the value is remembered and used for new sessions until you change the variable to a different value or the server exits. The change is visible to any client that accesses the global variable. However, the change affects the corresponding session variable only for clients that connect after the change. The global variable change does not affect the session variable for any current client sessions (not even the session within which the SET GLOBAL statement occurred).

To make a global system variable setting permanent so that it applies across server restarts, you should also set it in an option file.

To set a GLOBAL value to the compiled-in MySQL default value or a SESSION variable to the current corresponding GLOBAL value, set the variable to the value DEFAULT. For example, the following two statements are identical in setting the session value of max_join_size to the current global value:

SET @@session.max_join_size=DEFAULT;
SET @@session.max_join_size=@@global.max_join_size;

Not all system variables can be set to DEFAULT. In such cases, assigning DEFAULT results in an error.

An error occurs for attempts to assign DEFAULT to user-defined variables, stored procedure or function parameters, or stored program local variables.

To refer to the value of a system variable in expressions, use one of the @@-modifiers. For example, you can retrieve values in a SELECT statement like this:

SELECT @@global.sql_mode, @@session.sql_mode, @@sql_mode;

For a reference to a system variable in an expression as @@var_name (rather than with @@global. or @@session.), MySQL returns the session value if it exists and the global value otherwise. This differs from SET @@var_name = expr, which always refers to the session value.

Suffixes for specifying a value multiplier can be used when setting a variable at server startup, but not to set the value with SET at runtime. On the other hand, with SET you can assign a variable's value using an expression, which is not true when you set a variable at server startup. For example, the first of the following lines is legal at server startup, but the second is not:

shell> mysql --max_allowed_packet=16M
shell> mysql --max_allowed_packet=16*1024*1024

Conversely, the second of the following lines is legal at runtime, but the first is not:

mysql> SET GLOBAL max_allowed_packet=16M;
mysql> SET GLOBAL max_allowed_packet=16*1024*1024;
Note

Some system variables can be enabled with the SET statement by setting them to ON or 1, or disabled by setting them to OFF or 0. However, to set such a variable on the command line or in an option file, you must set it to 1 or 0; setting it to ON or OFF will not work. For example, on the command line, --delay_key_write=1 works but --delay_key_write=ON does not.

To display system variable names and values, use the SHOW VARIABLES statement:

mysql> SHOW VARIABLES;
+---------------------------------+-----------------------------------+
| Variable_name                   | Value                             |
+---------------------------------+-----------------------------------+
| auto_increment_increment        | 1                                 |
| auto_increment_offset           | 1                                 |
| automatic_sp_privileges         | ON                                |
| back_log                        | 50                                |
| basedir                         | /home/mysql/                      |
| binlog_cache_size               | 32768                             |
| bulk_insert_buffer_size         | 8388608                           |
| character_set_client            | latin1                            |
| character_set_connection        | latin1                            |
| character_set_database          | latin1                            |
| character_set_results           | latin1                            |
| character_set_server            | latin1                            |
| character_set_system            | utf8                              |
| character_sets_dir              | /home/mysql/share/mysql/charsets/ |
| collation_connection            | latin1_swedish_ci                 |
| collation_database              | latin1_swedish_ci                 |
| collation_server                | latin1_swedish_ci                 |
...
| innodb_autoextend_increment     | 8                                 |
| innodb_buffer_pool_size         | 8388608                           |
| innodb_checksums                | ON                                |
| innodb_commit_concurrency       | 0                                 |
| innodb_concurrency_tickets      | 500                               |
| innodb_data_file_path           | ibdata1:10M:autoextend            |
| innodb_data_home_dir            |                                   |
...
| version                         | 5.1.6-alpha-log                   |
| version_comment                 | Source distribution               |
| version_compile_machine         | i686                              |
| version_compile_os              | suse-linux                        |
| wait_timeout                    | 28800                             |
+---------------------------------+-----------------------------------+

With a LIKE clause, the statement displays only those variables that match the pattern. To obtain a specific variable name, use a LIKE clause as shown:

SHOW VARIABLES LIKE 'max_join_size';
SHOW SESSION VARIABLES LIKE 'max_join_size';

To get a list of variables whose name match a pattern, use the % wildcard character in a LIKE clause:

SHOW VARIABLES LIKE '%size%';
SHOW GLOBAL VARIABLES LIKE '%size%';

Wildcard characters can be used in any position within the pattern to be matched. Strictly speaking, because _ is a wildcard that matches any single character, you should escape it as \_ to match it literally. In practice, this is rarely necessary.

For SHOW VARIABLES, if you specify neither GLOBAL nor SESSION, MySQL returns SESSION values.

The reason for requiring the GLOBAL keyword when setting GLOBAL-only variables but not when retrieving them is to prevent problems in the future:

  • Were we to remove a SESSION variable that has the same name as a GLOBAL variable, a client with the SUPER privilege might accidentally change the GLOBAL variable rather than just the SESSION variable for its own connection.

  • Were we to add a SESSION variable with the same name as a GLOBAL variable, a client that intends to change the GLOBAL variable might find only its own SESSION variable changed.

6.1.6.1 Structured System Variables

A structured variable differs from a regular system variable in two respects:

  • Its value is a structure with components that specify server parameters considered to be closely related.

  • There might be several instances of a given type of structured variable. Each one has a different name and refers to a different resource maintained by the server.

MySQL supports one structured variable type, which specifies parameters governing the operation of key caches. A key cache structured variable has these components:

This section describes the syntax for referring to structured variables. Key cache variables are used for syntax examples, but specific details about how key caches operate are found elsewhere, in Section 9.10.2, “The MyISAM Key Cache”.

To refer to a component of a structured variable instance, you can use a compound name in instance_name.component_name format. Examples:

hot_cache.key_buffer_size
hot_cache.key_cache_block_size
cold_cache.key_cache_block_size

For each structured system variable, an instance with the name of default is always predefined. If you refer to a component of a structured variable without any instance name, the default instance is used. Thus, default.key_buffer_size and key_buffer_size both refer to the same system variable.

Structured variable instances and components follow these naming rules:

  • For a given type of structured variable, each instance must have a name that is unique within variables of that type. However, instance names need not be unique across structured variable types. For example, each structured variable has an instance named default, so default is not unique across variable types.

  • The names of the components of each structured variable type must be unique across all system variable names. If this were not true (that is, if two different types of structured variables could share component member names), it would not be clear which default structured variable to use for references to member names that are not qualified by an instance name.

  • If a structured variable instance name is not legal as an unquoted identifier, refer to it as a quoted identifier using backticks. For example, hot-cache is not legal, but `hot-cache` is.

  • global, session, and local are not legal instance names. This avoids a conflict with notation such as @@global.var_name for referring to nonstructured system variables.

Currently, the first two rules have no possibility of being violated because the only structured variable type is the one for key caches. These rules will assume greater significance if some other type of structured variable is created in the future.

With one exception, you can refer to structured variable components using compound names in any context where simple variable names can occur. For example, you can assign a value to a structured variable using a command-line option:

shell> mysqld --hot_cache.key_buffer_size=64K

In an option file, use this syntax:

[mysqld]
hot_cache.key_buffer_size=64K

If you start the server with this option, it creates a key cache named hot_cache with a size of 64KB in addition to the default key cache that has a default size of 8MB.

Suppose that you start the server as follows:

shell> mysqld --key_buffer_size=256K \
         --extra_cache.key_buffer_size=128K \
         --extra_cache.key_cache_block_size=2048

In this case, the server sets the size of the default key cache to 256KB. (You could also have written --default.key_buffer_size=256K.) In addition, the server creates a second key cache named extra_cache that has a size of 128KB, with the size of block buffers for caching table index blocks set to 2048 bytes.

The following example starts the server with three different key caches having sizes in a 3:1:1 ratio:

shell> mysqld --key_buffer_size=6M \
         --hot_cache.key_buffer_size=2M \
         --cold_cache.key_buffer_size=2M

Structured variable values may be set and retrieved at runtime as well. For example, to set a key cache named hot_cache to a size of 10MB, use either of these statements:

mysql> SET GLOBAL hot_cache.key_buffer_size = 10*1024*1024;
mysql> SET @@global.hot_cache.key_buffer_size = 10*1024*1024;

To retrieve the cache size, do this:

mysql> SELECT @@global.hot_cache.key_buffer_size;

However, the following statement does not work. The variable is not interpreted as a compound name, but as a simple string for a LIKE pattern-matching operation:

mysql> SHOW GLOBAL VARIABLES LIKE 'hot_cache.key_buffer_size';

This is the exception to being able to use structured variable names anywhere a simple variable name may occur.

6.1.6.2 Dynamic System Variables

Many server system variables are dynamic and can be set at runtime using SET GLOBAL or SET SESSION. You can also obtain their values using SELECT. See Section 6.1.6, “Using System Variables”.

The following table shows the full list of all dynamic system variables. The last column indicates for each variable whether GLOBAL or SESSION (or both) apply. The table also lists session options that can be set with the SET statement. Section 6.1.5, “Server System Variables”, discusses these options.

Variables that have a type of string take a string value. Variables that have a type of numeric take a numeric value. Variables that have a type of boolean can be set to 0, 1, ON or OFF. Variables that are marked as enumeration normally should be set to one of the available values for the variable, but can also be set to the number that corresponds to the desired enumeration value. For enumerated system variables, the first enumeration value corresponds to 0. This differs from ENUM columns, for which the first enumeration value corresponds to 1.

Table 6.3 Dynamic Variable Summary

Variable NameVariable TypeVariable Scope
audit_log_connection_policyenumerationGLOBAL
audit_log_exclude_accountsstringGLOBAL
audit_log_flushbooleanGLOBAL
audit_log_include_accountsstringGLOBAL
audit_log_rotate_on_sizeintegerGLOBAL
audit_log_statement_policyenumerationGLOBAL
auto_increment_incrementintegerGLOBAL | SESSION
auto_increment_offsetintegerGLOBAL | SESSION
autocommitbooleanGLOBAL | SESSION
automatic_sp_privilegesbooleanGLOBAL
avoid_temporal_upgradebooleanGLOBAL
big_tablesbooleanGLOBAL | SESSION
binlog_cache_sizeintegerGLOBAL
binlog_checksumstringGLOBAL
binlog_direct_non_transactional_updatesbooleanGLOBAL | SESSION
binlog_error_actionenumerationGLOBAL | SESSION
binlog_formatenumerationGLOBAL | SESSION
binlog_group_commit_sync_delayintegerGLOBAL
binlog_group_commit_sync_no_delay_countintegerGLOBAL
binlog_max_flush_queue_timeintegerGLOBAL
binlog_order_commitsbooleanGLOBAL
binlog_row_image=image_typeenumerationGLOBAL | SESSION
binlog_rows_query_log_eventsbooleanGLOBAL | SESSION
binlog_stmt_cache_sizeintegerGLOBAL
binlogging_impossible_modeenumerationGLOBAL | SESSION
block_encryption_modestringGLOBAL | SESSION
bulk_insert_buffer_sizeintegerGLOBAL | SESSION
character_set_clientstringGLOBAL | SESSION
character_set_connectionstringGLOBAL | SESSION
character_set_databasestringGLOBAL | SESSION
character_set_filesystemstringGLOBAL | SESSION
character_set_resultsstringGLOBAL | SESSION
character_set_serverstringGLOBAL | SESSION
check_proxy_usersbooleanGLOBAL
collation_connectionstringGLOBAL | SESSION
collation_databasestringGLOBAL | SESSION
collation_serverstringGLOBAL | SESSION
completion_typeenumerationGLOBAL | SESSION
concurrent_insertenumerationGLOBAL
connect_timeoutintegerGLOBAL
connection_control_failed_connections_thresholdintegerGLOBAL
connection_control_max_connection_delayintegerGLOBAL
connection_control_min_connection_delayintegerGLOBAL
debugstringGLOBAL | SESSION
debug_syncstringSESSION
default_password_lifetimeintegerGLOBAL
default_storage_engineenumerationGLOBAL | SESSION
default_tmp_storage_engineenumerationGLOBAL | SESSION
default_week_formatintegerGLOBAL | SESSION
delay_key_writeenumerationGLOBAL
delayed_insert_limitintegerGLOBAL
delayed_insert_timeoutintegerGLOBAL
delayed_queue_sizeintegerGLOBAL
div_precision_incrementintegerGLOBAL | SESSION
end_markers_in_jsonbooleanGLOBAL | SESSION
enforce_gtid_consistencyenumerationGLOBAL
enforce_gtid_consistencyenumerationGLOBAL
eq_range_index_dive_limitintegerGLOBAL | SESSION
event_schedulerenumerationGLOBAL
executed_gtids_compression_periodintegerGLOBAL
expire_logs_daysintegerGLOBAL
explicit_defaults_for_timestampbooleanGLOBAL | SESSION
flushbooleanGLOBAL
flush_timeintegerGLOBAL
foreign_key_checksbooleanGLOBAL | SESSION
ft_boolean_syntaxstringGLOBAL
general_logbooleanGLOBAL
general_log_filefilenameGLOBAL
group_concat_max_lenintegerGLOBAL | SESSION
group_replication_allow_local_disjoint_gtids_joinbooleanGLOBAL
group_replication_allow_local_lower_version_joinbooleanGLOBAL
group_replication_auto_increment_incrementintegerGLOBAL
group_replication_bootstrap_groupbooleanGLOBAL
group_replication_components_stop_timeoutintegerGLOBAL
group_replication_compression_thresholdintegerGLOBAL
group_replication_enforce_update_everywhere_checksbooleanGLOBAL
group_replication_flow_control_applier_thresholdintegerGLOBAL
group_replication_flow_control_certifier_thresholdintegerGLOBAL
group_replication_flow_control_modeenumerationGLOBAL
group_replication_force_membersstringGLOBAL
group_replication_group_namestringGLOBAL
group_replication_group_seedsstringGLOBAL
group_replication_gtid_assignment_block_sizeintegerGLOBAL
group_replication_ip_whiteliststringGLOBAL
group_replication_local_addressstringGLOBAL
group_replication_poll_spin_loopsintegerGLOBAL
group_replication_recovery_complete_atenumerationGLOBAL
group_replication_recovery_reconnect_intervalintegerGLOBAL
group_replication_recovery_retry_countintegerGLOBAL
group_replication_recovery_ssl_castringGLOBAL
group_replication_recovery_ssl_capathstringGLOBAL
group_replication_recovery_ssl_certstringGLOBAL
group_replication_recovery_ssl_cipherstringGLOBAL
group_replication_recovery_ssl_crlstringGLOBAL
group_replication_recovery_ssl_crlpathstringGLOBAL
group_replication_recovery_ssl_keystringGLOBAL
group_replication_recovery_ssl_verify_server_certbooleanGLOBAL
group_replication_recovery_use_sslbooleanGLOBAL
group_replication_single_primary_modebooleanGLOBAL
group_replication_ssl_modeenumerationGLOBAL
group_replication_start_on_bootbooleanGLOBAL
gtid_executed_compression_periodintegerGLOBAL
gtid_modeenumerationGLOBAL
gtid_modeenumerationGLOBAL
gtid_nextenumerationSESSION
gtid_purgedstringGLOBAL
host_cache_sizeintegerGLOBAL
identityintegerSESSION
init_connectstringGLOBAL
init_slavestringGLOBAL
innodb_adaptive_flushingbooleanGLOBAL
innodb_adaptive_flushing_lwmintegerGLOBAL
innodb_adaptive_hash_indexbooleanGLOBAL
innodb_adaptive_max_sleep_delayintegerGLOBAL
innodb_api_bk_commit_intervalintegerGLOBAL
innodb_api_trx_levelintegerGLOBAL
innodb_autoextend_incrementintegerGLOBAL
innodb_background_drop_list_emptybooleanGLOBAL
innodb_buffer_pool_dump_at_shutdownbooleanGLOBAL
innodb_buffer_pool_dump_nowbooleanGLOBAL
innodb_buffer_pool_dump_pctintegerGLOBAL
innodb_buffer_pool_filenamefilenameGLOBAL
innodb_buffer_pool_load_abortbooleanGLOBAL
innodb_buffer_pool_load_nowbooleanGLOBAL
innodb_buffer_pool_sizeintegerGLOBAL
innodb_change_buffer_max_sizeintegerGLOBAL
innodb_change_bufferingenumerationGLOBAL
innodb_change_buffering_debugintegerGLOBAL
innodb_checksum_algorithmenumerationGLOBAL
innodb_cmp_per_index_enabledbooleanGLOBAL
innodb_commit_concurrencyintegerGLOBAL
innodb_compress_debugenumerationGLOBAL
innodb_compression_failure_threshold_pctintegerGLOBAL
innodb_compression_levelintegerGLOBAL
innodb_compression_pad_pct_maxintegerGLOBAL
innodb_concurrency_ticketsintegerGLOBAL
innodb_create_intrinsicbooleanSESSION
innodb_deadlock_detectbooleanGLOBAL
innodb_default_row_formatenumerationGLOBAL
innodb_disable_resize_buffer_pool_debugbooleanGLOBAL
innodb_disable_sort_file_cachebooleanGLOBAL
innodb_fast_shutdownintegerGLOBAL
innodb_fil_make_page_dirty_debugintegerGLOBAL
innodb_file_formatstringGLOBAL
innodb_file_format_maxstringGLOBAL
innodb_file_per_tablebooleanGLOBAL
innodb_fill_factorintegerGLOBAL
innodb_flush_log_at_timeoutintegerGLOBAL
innodb_flush_log_at_trx_commitenumerationGLOBAL
innodb_flush_neighborsenumerationGLOBAL
innodb_flush_syncbooleanGLOBAL
innodb_flushing_avg_loopsintegerGLOBAL
innodb_ft_aux_tablestringGLOBAL
innodb_ft_enable_diag_printbooleanGLOBAL
innodb_ft_enable_stopwordbooleanGLOBAL
innodb_ft_num_word_optimizeintegerGLOBAL
innodb_ft_result_cache_limitintegerGLOBAL
innodb_ft_server_stopword_tablestringGLOBAL
innodb_ft_user_stopword_tablestringGLOBAL | SESSION
innodb_io_capacityintegerGLOBAL
innodb_io_capacity_maxintegerGLOBAL
innodb_large_prefixbooleanGLOBAL
innodb_limit_optimistic_insert_debugintegerGLOBAL
innodb_lock_wait_timeoutintegerGLOBAL | SESSION
innodb_log_checksum_algorithmenumerationGLOBAL
innodb_log_checksumsbooleanGLOBAL
innodb_log_compressed_pagesbooleanGLOBAL
innodb_log_write_ahead_sizeintegerGLOBAL
innodb_lru_scan_depthintegerGLOBAL
innodb_max_dirty_pages_pctnumericGLOBAL
innodb_max_dirty_pages_pct_lwmnumericGLOBAL
innodb_max_purge_lagintegerGLOBAL
innodb_max_purge_lag_delayintegerGLOBAL
innodb_max_undo_log_sizeintegerGLOBAL
innodb_merge_threshold_set_all_debugintegerGLOBAL
innodb_monitor_disablestringGLOBAL
innodb_monitor_enablestringGLOBAL
innodb_monitor_resetstringGLOBAL
innodb_monitor_reset_allstringGLOBAL
innodb_old_blocks_pctintegerGLOBAL
innodb_old_blocks_timeintegerGLOBAL
innodb_online_alter_log_max_sizeintegerGLOBAL
innodb_optimize_fulltext_onlybooleanGLOBAL
innodb_optimize_point_storagebooleanSESSION
innodb_print_all_deadlocksbooleanGLOBAL
innodb_purge_batch_sizeintegerGLOBAL
innodb_purge_rseg_truncate_frequencyintegerGLOBAL
innodb_random_read_aheadbooleanGLOBAL
innodb_read_ahead_thresholdintegerGLOBAL
innodb_replication_delayintegerGLOBAL
innodb_rollback_segmentsintegerGLOBAL
innodb_saved_page_number_debugintegerGLOBAL
innodb_spin_wait_delayintegerGLOBAL
innodb_stats_auto_recalcbooleanGLOBAL
innodb_stats_include_delete_markedbooleanGLOBAL
innodb_stats_methodenumerationGLOBAL
innodb_stats_on_metadatabooleanGLOBAL
innodb_stats_persistentbooleanGLOBAL
innodb_stats_persistent_sample_pagesintegerGLOBAL
innodb_stats_sample_pagesintegerGLOBAL
innodb_stats_transient_sample_pagesintegerGLOBAL
innodb_status_outputbooleanGLOBAL
innodb_status_output_locksbooleanGLOBAL
innodb_strict_modebooleanGLOBAL | SESSION
innodb_support_xabooleanGLOBAL | SESSION
innodb_sync_spin_loopsintegerGLOBAL
innodb_table_locksbooleanGLOBAL | SESSION
innodb_thread_concurrencyintegerGLOBAL
innodb_thread_sleep_delayintegerGLOBAL
innodb_tmpdirdirnameGLOBAL | SESSION
innodb_trx_purge_view_update_only_debugbooleanGLOBAL
innodb_trx_rseg_n_slots_debugintegerGLOBAL
innodb_undo_log_truncatebooleanGLOBAL
innodb_undo_logsintegerGLOBAL
insert_idintegerSESSION
interactive_timeoutintegerGLOBAL | SESSION
internal_tmp_disk_storage_engineenumerationGLOBAL
join_buffer_sizeintegerGLOBAL | SESSION
keep_files_on_createbooleanGLOBAL | SESSION
key_buffer_sizeintegerGLOBAL
key_cache_age_thresholdintegerGLOBAL
key_cache_block_sizeintegerGLOBAL
key_cache_division_limitintegerGLOBAL
keyring_file_datafilenameGLOBAL
keyring_okv_conf_dirdirnameGLOBAL
last_insert_idintegerSESSION
lc_messagesstringGLOBAL | SESSION
lc_time_namesstringGLOBAL | SESSION
local_infilebooleanGLOBAL
lock_wait_timeoutintegerGLOBAL | SESSION
log_backward_compatible_user_definitionsbooleanGLOBAL
log_bin_trust_function_creatorsbooleanGLOBAL
log_builtin_as_identified_by_passwordbooleanGLOBAL
log_error_verbosityintegerGLOBAL
log_outputsetGLOBAL
log_queries_not_using_indexesbooleanGLOBAL
log_slow_admin_statementsbooleanGLOBAL
log_slow_slave_statementsbooleanGLOBAL
log_statements_unsafe_for_binlogbooleanGLOBAL
log_syslogbooleanGLOBAL
log_syslog_facilitystringGLOBAL
log_syslog_include_pidbooleanGLOBAL
log_syslog_tagstringGLOBAL
log_throttle_queries_not_using_indexesintegerGLOBAL
log_timestampsenumerationGLOBAL
log_warningsintegerGLOBAL
long_query_timenumericGLOBAL | SESSION
low_priority_updatesbooleanGLOBAL | SESSION
master_info_repositorystringGLOBAL
master_verify_checksumbooleanGLOBAL
max_allowed_packetintegerGLOBAL | SESSION
max_binlog_cache_sizeintegerGLOBAL
max_binlog_sizeintegerGLOBAL
max_binlog_stmt_cache_sizeintegerGLOBAL
max_connect_errorsintegerGLOBAL
max_connectionsintegerGLOBAL
max_delayed_threadsintegerGLOBAL | SESSION
max_error_countintegerGLOBAL | SESSION
max_execution_timeintegerGLOBAL | SESSION
max_heap_table_sizeintegerGLOBAL | SESSION
max_insert_delayed_threadsintegerGLOBAL | SESSION
max_join_sizeintegerGLOBAL | SESSION
max_length_for_sort_dataintegerGLOBAL | SESSION
max_points_in_geometryintegerGLOBAL
max_prepared_stmt_countintegerGLOBAL
max_relay_log_sizeintegerGLOBAL
max_seeks_for_keyintegerGLOBAL | SESSION
max_sort_lengthintegerGLOBAL | SESSION
max_sp_recursion_depthintegerGLOBAL | SESSION
max_statement_timeintegerGLOBAL | SESSION
max_tmp_tablesintegerGLOBAL | SESSION
max_user_connectionsintegerGLOBAL | SESSION
max_write_lock_countintegerGLOBAL
min_examined_row_limitintegerGLOBAL | SESSION
multi_range_countintegerGLOBAL | SESSION
myisam_data_pointer_sizeintegerGLOBAL
myisam_max_sort_file_sizeintegerGLOBAL
myisam_repair_threadsintegerGLOBAL | SESSION
myisam_sort_buffer_sizeintegerGLOBAL | SESSION
myisam_stats_methodenumerationGLOBAL | SESSION
myisam_use_mmapbooleanGLOBAL
mysql_firewall_modebooleanGLOBAL
mysql_firewall_tracebooleanGLOBAL
mysql_native_password_proxy_usersbooleanGLOBAL
mysqlx_connect_timeoutintegerGLOBAL
mysqlx_max_connectionsintegerGLOBAL
ndb-allow-copying-alter-tablebooleanGLOBAL | SESSION
ndb_autoincrement_prefetch_szintegerGLOBAL | SESSION
ndb_blob_read_batch_bytesintegerGLOBAL | SESSION
ndb_blob_write_batch_bytesintegerGLOBAL | SESSION
ndb_cache_check_timeintegerGLOBAL
ndb_clear_apply_statusbooleanGLOBAL
ndb_data_node_neighbourintegerGLOBAL
ndb_default_column_formatenumerationGLOBAL
ndb_default_column_formatenumerationGLOBAL
ndb_deferred_constraintsintegerGLOBAL | SESSION
ndb_deferred_constraintsintegerGLOBAL | SESSION
ndb_distributionenumerationGLOBAL
ndb_distribution={KEYHASH|LINHASH}enumerationGLOBAL
ndb_eventbuffer_free_percentintegerGLOBAL
ndb_eventbuffer_max_allocintegerGLOBAL
ndb_extra_loggingintegerGLOBAL
ndb_force_sendbooleanGLOBAL | SESSION
ndb_fully_replicatedbooleanGLOBAL | SESSION
ndb_index_stat_enablebooleanGLOBAL | SESSION
ndb_index_stat_optionstringGLOBAL | SESSION
ndb_join_pushdownbooleanGLOBAL | SESSION
ndb_log_binbooleanGLOBAL | SESSION
ndb_log_binlog_indexbooleanGLOBAL
ndb_log_empty_epochsbooleanGLOBAL
ndb_log_empty_epochsbooleanGLOBAL
ndb_log_empty_updatebooleanGLOBAL
ndb_log_empty_updatebooleanGLOBAL
ndb_log_exclusive_readsbooleanGLOBAL | SESSION
ndb_log_exclusive_readsbooleanGLOBAL | SESSION
ndb_log_updated_onlybooleanGLOBAL
ndb_optimization_delayintegerGLOBAL
ndb_read_backupbooleanGLOBAL
ndb_recv_thread_cpu_maskbitmapGLOBAL
ndb_report_thresh_binlog_epoch_slipintegerGLOBAL
ndb_report_thresh_binlog_mem_usageintegerGLOBAL
ndb_show_foreign_key_mock_tablesbooleanGLOBAL
ndb_slave_last_conflict_epochenumerationGLOBAL
ndb_table_no_loggingbooleanSESSION
ndb_table_temporarybooleanSESSION
ndb_use_exact_countbooleanGLOBAL | SESSION
ndb_use_transactionsbooleanGLOBAL | SESSION
ndbinfo_max_bytesintegerGLOBAL | SESSION
ndbinfo_max_rowsintegerGLOBAL | SESSION
ndbinfo_offlinebooleanGLOBAL
ndbinfo_show_hiddenbooleanGLOBAL | SESSION
ndbinfo_table_prefixstringGLOBAL | SESSION
net_buffer_lengthintegerGLOBAL | SESSION
net_read_timeoutintegerGLOBAL | SESSION
net_retry_countintegerGLOBAL | SESSION
net_write_timeoutintegerGLOBAL | SESSION
newbooleanGLOBAL | SESSION
offline_modebooleanGLOBAL
old_alter_tablebooleanGLOBAL | SESSION
old_passwordsenumerationGLOBAL | SESSION
optimizer_prune_levelbooleanGLOBAL | SESSION
optimizer_search_depthintegerGLOBAL | SESSION
optimizer_switchsetGLOBAL | SESSION
optimizer_tracestringGLOBAL | SESSION
optimizer_trace_featuresstringGLOBAL | SESSION
optimizer_trace_limitintegerGLOBAL | SESSION
optimizer_trace_max_mem_sizeintegerGLOBAL | SESSION
optimizer_trace_offsetintegerGLOBAL | SESSION
parser_max_mem_sizeintegerGLOBAL | SESSION
preload_buffer_sizeintegerGLOBAL | SESSION
profilingbooleanGLOBAL | SESSION
profiling_history_sizeintegerGLOBAL | SESSION
pseudo_slave_modeintegerSESSION
pseudo_thread_idintegerSESSION
query_alloc_block_sizeintegerGLOBAL | SESSION
query_cache_limitintegerGLOBAL
query_cache_min_res_unitintegerGLOBAL
query_cache_sizeintegerGLOBAL
query_cache_typeenumerationGLOBAL | SESSION
query_cache_wlock_invalidatebooleanGLOBAL | SESSION
query_prealloc_sizeintegerGLOBAL | SESSION
rand_seed1integerSESSION
rand_seed2integerSESSION
range_alloc_block_sizeintegerGLOBAL | SESSION
range_optimizer_max_mem_sizeintegerGLOBAL | SESSION
rbr_exec_modeenumerationSESSION
read_buffer_sizeintegerGLOBAL | SESSION
read_onlybooleanGLOBAL
read_rnd_buffer_sizeintegerGLOBAL | SESSION
relay_log_info_repositorystringGLOBAL
relay_log_purgebooleanGLOBAL
require_secure_transportbooleanGLOBAL
rewriter_enabledbooleanGLOBAL
rewriter_verboseintegerGLOBAL
rpl_semi_sync_master_enabledbooleanGLOBAL
rpl_semi_sync_master_timeoutintegerGLOBAL
rpl_semi_sync_master_trace_levelintegerGLOBAL
rpl_semi_sync_master_wait_for_slave_countintegerGLOBAL
rpl_semi_sync_master_wait_no_slavebooleanGLOBAL
rpl_semi_sync_master_wait_pointenumerationGLOBAL
rpl_semi_sync_slave_enabledbooleanGLOBAL
rpl_semi_sync_slave_trace_levelintegerGLOBAL
rpl_stop_slave_timeoutintegerGLOBAL
secure_authbooleanGLOBAL
server_idintegerGLOBAL
session_track_gtidsenumerationGLOBAL | SESSION
session_track_schemabooleanGLOBAL | SESSION
session_track_state_changebooleanGLOBAL | SESSION
session_track_system_variablesstringGLOBAL | SESSION
sha256_password_proxy_usersbooleanGLOBAL
show_compatibility_56booleanGLOBAL
show_old_temporalsbooleanGLOBAL | SESSION
slave_allow_batchingbooleanGLOBAL
slave_checkpoint_group=#integerGLOBAL
slave_checkpoint_period=#integerGLOBAL
slave_compressed_protocolbooleanGLOBAL
slave_exec_modeenumerationGLOBAL
slave_max_allowed_packetintegerGLOBAL
slave_net_timeoutintegerGLOBAL
slave_parallel_typeenumerationGLOBAL
slave_parallel_workersintegerGLOBAL
slave_pending_jobs_size_maxintegerGLOBAL
slave_preserve_commit_orderbooleanGLOBAL
slave_rows_search_algorithms=listsetGLOBAL
slave_sql_verify_checksumbooleanGLOBAL
slave_transaction_retriesintegerGLOBAL
slow_launch_timeintegerGLOBAL
slow_query_logbooleanGLOBAL
slow_query_log_filefilenameGLOBAL
sort_buffer_sizeintegerGLOBAL | SESSION
sql_auto_is_nullbooleanGLOBAL | SESSION
sql_big_selectsbooleanGLOBAL | SESSION
sql_buffer_resultbooleanGLOBAL | SESSION
sql_log_binbooleanSESSION
sql_log_offbooleanGLOBAL | SESSION
sql_modesetGLOBAL | SESSION
sql_notesbooleanGLOBAL | SESSION
sql_quote_show_createbooleanGLOBAL | SESSION
sql_safe_updatesbooleanGLOBAL | SESSION
sql_select_limitintegerGLOBAL | SESSION
sql_slave_skip_counterintegerGLOBAL
sql_warningsbooleanGLOBAL | SESSION
storage_engineenumerationGLOBAL | SESSION
stored_program_cacheintegerGLOBAL
super_read_onlybooleanGLOBAL
sync_binlogintegerGLOBAL
sync_frmbooleanGLOBAL
sync_master_infointegerGLOBAL
sync_relay_logintegerGLOBAL
sync_relay_log_infointegerGLOBAL
table_definition_cacheintegerGLOBAL
table_open_cacheintegerGLOBAL
thread_cache_sizeintegerGLOBAL
thread_pool_high_priority_connectionintegerGLOBAL | SESSION
thread_pool_max_unused_threadsintegerGLOBAL
thread_pool_prio_kickup_timerintegerGLOBAL | SESSION
thread_pool_stall_limitintegerGLOBAL
time_zonestringGLOBAL | SESSION
timed_mutexesbooleanGLOBAL
timestampnumericSESSION
tmp_table_sizeintegerGLOBAL | SESSION
transaction_alloc_block_sizeintegerGLOBAL | SESSION
transaction_allow_batchingbooleanSESSION
transaction_prealloc_sizeintegerGLOBAL | SESSION
transaction_write_set_extractionenumerationGLOBAL | SESSION
tx_isolationenumerationGLOBAL | SESSION
tx_read_onlybooleanGLOBAL | SESSION
unique_checksbooleanGLOBAL | SESSION
updatable_views_with_limitbooleanGLOBAL | SESSION
validate_password_check_user_namebooleanGLOBAL
validate_password_dictionary_filefilenameGLOBAL
validate_password_lengthintegerGLOBAL
validate_password_mixed_case_countintegerGLOBAL
validate_password_number_countintegerGLOBAL
validate_password_policyenumerationGLOBAL
validate_password_special_char_countintegerGLOBAL
version_tokens_sessionstringGLOBAL | SESSION
wait_timeoutintegerGLOBAL | SESSION

6.1.7 Server Status Variables

The MySQL server maintains many status variables that provide information about its operation. You can view these variables and their values by using the SHOW [GLOBAL | SESSION] STATUS statement (see Section 14.7.5.35, “SHOW STATUS Syntax”). The optional GLOBAL keyword aggregates the values over all connections, and SESSION shows the values for the current connection.

mysql> SHOW GLOBAL STATUS;
+-----------------------------------+------------+
| Variable_name                     | Value      |
+-----------------------------------+------------+
| Aborted_clients                   | 0          |
| Aborted_connects                  | 0          |
| Bytes_received                    | 155372598  |
| Bytes_sent                        | 1176560426 |
...
| Connections                       | 30023      |
| Created_tmp_disk_tables           | 0          |
| Created_tmp_files                 | 3          |
| Created_tmp_tables                | 2          |
...
| Threads_created                   | 217        |
| Threads_running                   | 88         |
| Uptime                            | 1389872    |
+-----------------------------------+------------+

Several status variables provide statement counts. To determine the number of statements executed, use these relationships:

  SUM(Com_xxx) + Qcache_hits
= Questions + statements executed within stored programs
= Queries

Many status variables are reset to 0 by the FLUSH STATUS statement.

The following table lists all available server status variables:

Table 6.4 Status Variable Summary

Variable NameVariable TypeVariable Scope
Aborted_clientsintegerGLOBAL
Aborted_connectsintegerGLOBAL
Audit_log_current_sizeintegerGLOBAL
Audit_log_event_max_drop_sizeintegerGLOBAL
Audit_log_eventsintegerGLOBAL
Audit_log_events_filteredintegerGLOBAL
Audit_log_events_lostintegerGLOBAL
Audit_log_events_writtenintegerGLOBAL
Audit_log_total_sizeintegerGLOBAL
Audit_log_write_waitsintegerGLOBAL
Binlog_cache_disk_useintegerGLOBAL
Binlog_cache_useintegerGLOBAL
Binlog_stmt_cache_disk_useintegerGLOBAL
Binlog_stmt_cache_useintegerGLOBAL
Bytes_receivedintegerGLOBAL | SESSION
Bytes_sentintegerGLOBAL | SESSION
Com_admin_commandsintegerGLOBAL | SESSION
Com_alter_dbintegerGLOBAL | SESSION
Com_alter_db_upgradeintegerGLOBAL | SESSION
Com_alter_eventintegerGLOBAL | SESSION
Com_alter_functionintegerGLOBAL | SESSION
Com_alter_procedureintegerGLOBAL | SESSION
Com_alter_serverintegerGLOBAL | SESSION
Com_alter_tableintegerGLOBAL | SESSION
Com_alter_tablespaceintegerGLOBAL | SESSION
Com_alter_userintegerGLOBAL | SESSION
Com_analyzeintegerGLOBAL | SESSION
Com_assign_to_keycacheintegerGLOBAL | SESSION
Com_beginintegerGLOBAL | SESSION
Com_binlogintegerGLOBAL | SESSION
Com_call_procedureintegerGLOBAL | SESSION
Com_change_dbintegerGLOBAL | SESSION
Com_change_masterintegerGLOBAL | SESSION
Com_change_repl_filterintegerGLOBAL | SESSION
Com_checkintegerGLOBAL | SESSION
Com_checksumintegerGLOBAL | SESSION
Com_commitintegerGLOBAL | SESSION
Com_create_dbintegerGLOBAL | SESSION
Com_create_eventintegerGLOBAL | SESSION
Com_create_functionintegerGLOBAL | SESSION
Com_create_indexintegerGLOBAL | SESSION
Com_create_procedureintegerGLOBAL | SESSION
Com_create_serverintegerGLOBAL | SESSION
Com_create_tableintegerGLOBAL | SESSION
Com_create_triggerintegerGLOBAL | SESSION
Com_create_udfintegerGLOBAL | SESSION
Com_create_userintegerGLOBAL | SESSION
Com_create_viewintegerGLOBAL | SESSION
Com_dealloc_sqlintegerGLOBAL | SESSION
Com_deleteintegerGLOBAL | SESSION
Com_delete_multiintegerGLOBAL | SESSION
Com_dointegerGLOBAL | SESSION
Com_drop_dbintegerGLOBAL | SESSION
Com_drop_eventintegerGLOBAL | SESSION
Com_drop_functionintegerGLOBAL | SESSION
Com_drop_indexintegerGLOBAL | SESSION
Com_drop_procedureintegerGLOBAL | SESSION
Com_drop_serverintegerGLOBAL | SESSION
Com_drop_tableintegerGLOBAL | SESSION
Com_drop_triggerintegerGLOBAL | SESSION
Com_drop_userintegerGLOBAL | SESSION
Com_drop_viewintegerGLOBAL | SESSION
Com_empty_queryintegerGLOBAL | SESSION
Com_execute_sqlintegerGLOBAL | SESSION
Com_explain_otherintegerGLOBAL | SESSION
Com_flushintegerGLOBAL | SESSION
Com_get_diagnosticsintegerGLOBAL | SESSION
Com_grantintegerGLOBAL | SESSION
Com_group_replication_start GLOBAL
Com_group_replication_stop GLOBAL
Com_ha_closeintegerGLOBAL | SESSION
Com_ha_openintegerGLOBAL | SESSION
Com_ha_readintegerGLOBAL | SESSION
Com_helpintegerGLOBAL | SESSION
Com_insertintegerGLOBAL | SESSION
Com_insert_selectintegerGLOBAL | SESSION
Com_install_pluginintegerGLOBAL | SESSION
Com_killintegerGLOBAL | SESSION
Com_loadintegerGLOBAL | SESSION
Com_lock_tablesintegerGLOBAL | SESSION
Com_optimizeintegerGLOBAL | SESSION
Com_preload_keysintegerGLOBAL | SESSION
Com_prepare_sqlintegerGLOBAL | SESSION
Com_purgeintegerGLOBAL | SESSION
Com_purge_before_dateintegerGLOBAL | SESSION
Com_release_savepointintegerGLOBAL | SESSION
Com_rename_tableintegerGLOBAL | SESSION
Com_rename_userintegerGLOBAL | SESSION
Com_repairintegerGLOBAL | SESSION
Com_replaceintegerGLOBAL | SESSION
Com_replace_selectintegerGLOBAL | SESSION
Com_resetintegerGLOBAL | SESSION
Com_resignalintegerGLOBAL | SESSION
Com_revokeintegerGLOBAL | SESSION
Com_revoke_allintegerGLOBAL | SESSION
Com_rollbackintegerGLOBAL | SESSION
Com_rollback_to_savepointintegerGLOBAL | SESSION
Com_savepointintegerGLOBAL | SESSION
Com_selectintegerGLOBAL | SESSION
Com_set_optionintegerGLOBAL | SESSION
Com_show_authorsintegerGLOBAL | SESSION
Com_show_binlog_eventsintegerGLOBAL | SESSION
Com_show_binlogsintegerGLOBAL | SESSION
Com_show_charsetsintegerGLOBAL | SESSION
Com_show_collationsintegerGLOBAL | SESSION
Com_show_contributorsintegerGLOBAL | SESSION
Com_show_create_dbintegerGLOBAL | SESSION
Com_show_create_eventintegerGLOBAL | SESSION
Com_show_create_funcintegerGLOBAL | SESSION
Com_show_create_procintegerGLOBAL | SESSION
Com_show_create_tableintegerGLOBAL | SESSION
Com_show_create_triggerintegerGLOBAL | SESSION
Com_show_create_userintegerGLOBAL | SESSION
Com_show_databasesintegerGLOBAL | SESSION
Com_show_engine_logsintegerGLOBAL | SESSION
Com_show_engine_mutexintegerGLOBAL | SESSION
Com_show_engine_statusintegerGLOBAL | SESSION
Com_show_errorsintegerGLOBAL | SESSION
Com_show_eventsintegerGLOBAL | SESSION
Com_show_fieldsintegerGLOBAL | SESSION
Com_show_function_codeintegerGLOBAL | SESSION
Com_show_function_statusintegerGLOBAL | SESSION
Com_show_grantsintegerGLOBAL | SESSION
Com_show_keysintegerGLOBAL | SESSION
Com_show_master_statusintegerGLOBAL | SESSION
Com_show_ndb_statusintegerGLOBAL | SESSION
Com_show_new_masterintegerGLOBAL | SESSION
Com_show_open_tablesintegerGLOBAL | SESSION
Com_show_pluginsintegerGLOBAL | SESSION
Com_show_privilegesintegerGLOBAL | SESSION
Com_show_procedure_codeintegerGLOBAL | SESSION
Com_show_procedure_statusintegerGLOBAL | SESSION
Com_show_processlistintegerGLOBAL | SESSION
Com_show_profileintegerGLOBAL | SESSION
Com_show_profilesintegerGLOBAL | SESSION
Com_show_relaylog_eventsintegerGLOBAL | SESSION
Com_show_slave_hostsintegerGLOBAL | SESSION
Com_show_slave_statusintegerGLOBAL | SESSION
Com_show_slave_status_nonblockingintegerGLOBAL | SESSION
Com_show_statusintegerGLOBAL | SESSION
Com_show_storage_enginesintegerGLOBAL | SESSION
Com_show_table_statusintegerGLOBAL | SESSION
Com_show_tablesintegerGLOBAL | SESSION
Com_show_triggersintegerGLOBAL | SESSION
Com_show_variablesintegerGLOBAL | SESSION
Com_show_warningsintegerGLOBAL | SESSION
Com_shutdownintegerGLOBAL | SESSION
Com_signalintegerGLOBAL | SESSION
Com_slave_startintegerGLOBAL | SESSION
Com_slave_stopintegerGLOBAL | SESSION
Com_stmt_closeintegerGLOBAL | SESSION
Com_stmt_executeintegerGLOBAL | SESSION
Com_stmt_fetchintegerGLOBAL | SESSION
Com_stmt_prepareintegerGLOBAL | SESSION
Com_stmt_reprepareintegerGLOBAL | SESSION
Com_stmt_resetintegerGLOBAL | SESSION
Com_stmt_send_long_dataintegerGLOBAL | SESSION
Com_truncateintegerGLOBAL | SESSION
Com_uninstall_pluginintegerGLOBAL | SESSION
Com_unlock_tablesintegerGLOBAL | SESSION
Com_updateintegerGLOBAL | SESSION
Com_update_multiintegerGLOBAL | SESSION
Com_xa_commitintegerGLOBAL | SESSION
Com_xa_endintegerGLOBAL | SESSION
Com_xa_prepareintegerGLOBAL | SESSION
Com_xa_recoverintegerGLOBAL | SESSION
Com_xa_rollbackintegerGLOBAL | SESSION
Com_xa_startintegerGLOBAL | SESSION
CompressionintegerSESSION
Connection_control_delay_generated GLOBAL
Connection_errors_acceptintegerGLOBAL
Connection_errors_internalintegerGLOBAL
Connection_errors_max_connectionsintegerGLOBAL
Connection_errors_peer_addrintegerGLOBAL
Connection_errors_selectintegerGLOBAL
Connection_errors_tcpwrapintegerGLOBAL
ConnectionsintegerGLOBAL
Created_tmp_disk_tablesintegerGLOBAL | SESSION
Created_tmp_filesintegerGLOBAL
Created_tmp_tablesintegerGLOBAL | SESSION
Delayed_errorsintegerGLOBAL
Delayed_insert_threadsintegerGLOBAL
Delayed_writesintegerGLOBAL
Firewall_access_deniedintegerGLOBAL
Firewall_access_grantedintegerGLOBAL
Firewall_cached_entriesintegerGLOBAL
Flush_commandsintegerGLOBAL
Handler_commitintegerGLOBAL | SESSION
Handler_deleteintegerGLOBAL | SESSION
Handler_discoverintegerGLOBAL | SESSION
Handler_external_lockintegerGLOBAL | SESSION
Handler_mrr_initintegerGLOBAL | SESSION
Handler_prepareintegerGLOBAL | SESSION
Handler_read_firstintegerGLOBAL | SESSION
Handler_read_keyintegerGLOBAL | SESSION
Handler_read_lastintegerGLOBAL | SESSION
Handler_read_nextintegerGLOBAL | SESSION
Handler_read_previntegerGLOBAL | SESSION
Handler_read_rndintegerGLOBAL | SESSION
Handler_read_rnd_nextintegerGLOBAL | SESSION
Handler_rollbackintegerGLOBAL | SESSION
Handler_savepointintegerGLOBAL | SESSION
Handler_savepoint_rollbackintegerGLOBAL | SESSION
Handler_updateintegerGLOBAL | SESSION
Handler_writeintegerGLOBAL | SESSION
Innodb_available_undo_logsintegerGLOBAL
Innodb_buffer_pool_bytes_dataintegerGLOBAL
Innodb_buffer_pool_bytes_dirtyintegerGLOBAL
Innodb_buffer_pool_dump_statusstringGLOBAL
Innodb_buffer_pool_load_statusstringGLOBAL
Innodb_buffer_pool_pages_dataintegerGLOBAL
Innodb_buffer_pool_pages_dirtyintegerGLOBAL
Innodb_buffer_pool_pages_flushedintegerGLOBAL
Innodb_buffer_pool_pages_freeintegerGLOBAL
Innodb_buffer_pool_pages_latchedintegerGLOBAL
Innodb_buffer_pool_pages_miscintegerGLOBAL
Innodb_buffer_pool_pages_totalintegerGLOBAL
Innodb_buffer_pool_read_aheadintegerGLOBAL
Innodb_buffer_pool_read_ahead_evictedintegerGLOBAL
Innodb_buffer_pool_read_ahead_rndintegerGLOBAL
Innodb_buffer_pool_read_requestsintegerGLOBAL
Innodb_buffer_pool_readsintegerGLOBAL
Innodb_buffer_pool_resize_statusstringGLOBAL
Innodb_buffer_pool_wait_freeintegerGLOBAL
Innodb_buffer_pool_write_requestsintegerGLOBAL
Innodb_data_fsyncsintegerGLOBAL
Innodb_data_pending_fsyncsintegerGLOBAL
Innodb_data_pending_readsintegerGLOBAL
Innodb_data_pending_writesintegerGLOBAL
Innodb_data_readintegerGLOBAL
Innodb_data_readsintegerGLOBAL
Innodb_data_writesintegerGLOBAL
Innodb_data_writtenintegerGLOBAL
Innodb_dblwr_pages_writtenintegerGLOBAL
Innodb_dblwr_writesintegerGLOBAL
Innodb_have_atomic_builtinsintegerGLOBAL
Innodb_log_waitsintegerGLOBAL
Innodb_log_write_requestsintegerGLOBAL
Innodb_log_writesintegerGLOBAL
Innodb_num_open_filesintegerGLOBAL
Innodb_os_log_fsyncsintegerGLOBAL
Innodb_os_log_pending_fsyncsintegerGLOBAL
Innodb_os_log_pending_writesintegerGLOBAL
Innodb_os_log_writtenintegerGLOBAL
Innodb_page_sizeintegerGLOBAL
Innodb_pages_createdintegerGLOBAL
Innodb_pages_readintegerGLOBAL
Innodb_pages_writtenintegerGLOBAL
Innodb_row_lock_current_waitsintegerGLOBAL
Innodb_row_lock_timeintegerGLOBAL
Innodb_row_lock_time_avgintegerGLOBAL
Innodb_row_lock_time_maxintegerGLOBAL
Innodb_row_lock_waitsintegerGLOBAL
Innodb_rows_deletedintegerGLOBAL
Innodb_rows_insertedintegerGLOBAL
Innodb_rows_readintegerGLOBAL
Innodb_rows_updatedintegerGLOBAL
Innodb_truncated_status_writesintegerGLOBAL
Key_blocks_not_flushedintegerGLOBAL
Key_blocks_unusedintegerGLOBAL
Key_blocks_usedintegerGLOBAL
Key_read_requestsintegerGLOBAL
Key_readsintegerGLOBAL
Key_write_requestsintegerGLOBAL
Key_writesintegerGLOBAL
Last_query_costnumericSESSION
Last_query_partial_plansintegerSESSION
Locked_connectsintegerGLOBAL
Max_execution_time_exceededintegerGLOBAL | SESSION
Max_execution_time_setintegerGLOBAL | SESSION
Max_execution_time_set_failedintegerGLOBAL | SESSION
Max_statement_time_exceededintegerGLOBAL | SESSION
Max_statement_time_setintegerGLOBAL | SESSION
Max_statement_time_set_failedintegerGLOBAL | SESSION
Max_used_connectionsintegerGLOBAL
Max_used_connections_timedatetimeGLOBAL
mecab_charsetstringGLOBAL
Mysqlx_addressstringGLOBAL
Mysqlx_bytes_receivedintegerGLOBAL | SESSION
Mysqlx_bytes_sentintegerGLOBAL | SESSION
Mysqlx_connection_accept_errorsintegerGLOBAL | SESSION
Mysqlx_connection_errorsintegerGLOBAL | SESSION
Mysqlx_connections_acceptedintegerGLOBAL
Mysqlx_connections_closedintegerGLOBAL
Mysqlx_connections_rejectedintegerGLOBAL
Mysqlx_crud_deleteintegerGLOBAL | SESSION
Mysqlx_crud_findintegerGLOBAL | SESSION
Mysqlx_crud_insertintegerGLOBAL | SESSION
Mysqlx_crud_updateintegerGLOBAL | SESSION
Mysqlx_errors_sentintegerGLOBAL | SESSION
Mysqlx_expect_closeintegerGLOBAL | SESSION
Mysqlx_expect_openintegerGLOBAL | SESSION
Mysqlx_init_errorintegerGLOBAL | SESSION
Mysqlx_notice_other_sentintegerGLOBAL | SESSION
Mysqlx_notice_warning_sentintegerGLOBAL | SESSION
Mysqlx_portstringGLOBAL
Mysqlx_rows_sentintegerGLOBAL | SESSION
Mysqlx_sessionsintegerGLOBAL
Mysqlx_sessions_acceptedintegerGLOBAL
Mysqlx_sessions_closedintegerGLOBAL
Mysqlx_sessions_fatal_errorintegerGLOBAL
Mysqlx_sessions_killedintegerGLOBAL
Mysqlx_sessions_rejectedintegerGLOBAL
Mysqlx_socketstringGLOBAL
Mysqlx_ssl_accept_renegotiatesintegerGLOBAL
Mysqlx_ssl_acceptsintegerGLOBAL
Mysqlx_ssl_activeintegerGLOBAL | SESSION
Mysqlx_ssl_cipherintegerGLOBAL | SESSION
Mysqlx_ssl_cipher_listintegerGLOBAL | SESSION
Mysqlx_ssl_ctx_verify_depthintegerGLOBAL | SESSION
Mysqlx_ssl_ctx_verify_modeintegerGLOBAL | SESSION
Mysqlx_ssl_finished_acceptsintegerGLOBAL
Mysqlx_ssl_server_not_afterintegerGLOBAL
Mysqlx_ssl_server_not_beforeintegerGLOBAL
Mysqlx_ssl_verify_depthintegerGLOBAL
Mysqlx_ssl_verify_modeintegerGLOBAL
Mysqlx_ssl_versionintegerGLOBAL | SESSION
Mysqlx_stmt_create_collectionintegerGLOBAL | SESSION
Mysqlx_stmt_create_collection_indexintegerGLOBAL | SESSION
Mysqlx_stmt_disable_noticesintegerGLOBAL | SESSION
Mysqlx_stmt_drop_collectionintegerGLOBAL | SESSION
Mysqlx_stmt_drop_collection_indexintegerGLOBAL | SESSION
Mysqlx_stmt_enable_noticesintegerGLOBAL | SESSION
Mysqlx_stmt_execute_sqlintegerGLOBAL | SESSION
Mysqlx_stmt_execute_xpluginintegerGLOBAL | SESSION
Mysqlx_stmt_kill_clientintegerGLOBAL | SESSION
Mysqlx_stmt_list_clientsintegerGLOBAL | SESSION
Mysqlx_stmt_list_noticesintegerGLOBAL | SESSION
Mysqlx_stmt_list_objectsintegerGLOBAL | SESSION
Mysqlx_stmt_pingintegerGLOBAL | SESSION
Mysqlx_worker_threadsintegerGLOBAL
Mysqlx_worker_threads_activeintegerGLOBAL
Ndb_api_bytes_received_countintegerGLOBAL
Ndb_api_bytes_received_count_sessionintegerSESSION
Ndb_api_bytes_received_count_slaveintegerGLOBAL
Ndb_api_bytes_sent_countintegerGLOBAL
Ndb_api_bytes_sent_count_slaveintegerGLOBAL
Ndb_api_event_bytes_count_injectorintegerGLOBAL
Ndb_api_event_data_count_injectorintegerGLOBAL
Ndb_api_event_nondata_count_injectorintegerGLOBAL
Ndb_api_pk_op_countintegerGLOBAL
Ndb_api_pk_op_count_sessionintegerSESSION
Ndb_api_pk_op_count_slaveintegerGLOBAL
Ndb_api_pruned_scan_countintegerGLOBAL
Ndb_api_pruned_scan_count_sessionintegerSESSION
Ndb_api_range_scan_count_slaveintegerGLOBAL
Ndb_api_read_row_countintegerGLOBAL
Ndb_api_read_row_count_sessionintegerSESSION
Ndb_api_scan_batch_count_slaveintegerGLOBAL
Ndb_api_table_scan_countintegerGLOBAL
Ndb_api_table_scan_count_sessionintegerSESSION
Ndb_api_trans_abort_countintegerGLOBAL
Ndb_api_trans_abort_count_sessionintegerSESSION
Ndb_api_trans_abort_count_slaveintegerGLOBAL
Ndb_api_trans_close_countintegerGLOBAL
Ndb_api_trans_close_count_sessionintegerSESSION
Ndb_api_trans_close_count_slaveintegerGLOBAL
Ndb_api_trans_commit_countintegerGLOBAL
Ndb_api_trans_commit_count_sessionintegerSESSION
Ndb_api_trans_commit_count_slaveintegerGLOBAL
Ndb_api_trans_local_read_row_count_slaveintegerGLOBAL
Ndb_api_trans_start_countintegerGLOBAL
Ndb_api_trans_start_count_sessionintegerSESSION
Ndb_api_trans_start_count_slaveintegerGLOBAL
Ndb_api_uk_op_countintegerGLOBAL
Ndb_api_uk_op_count_slaveintegerGLOBAL
Ndb_api_wait_exec_complete_countintegerGLOBAL
Ndb_api_wait_exec_complete_count_sessionintegerSESSION
Ndb_api_wait_exec_complete_count_slaveintegerGLOBAL
Ndb_api_wait_meta_request_countintegerGLOBAL
Ndb_api_wait_meta_request_count_sessionintegerSESSION
Ndb_api_wait_nanos_countintegerGLOBAL
Ndb_api_wait_nanos_count_sessionintegerSESSION
Ndb_api_wait_nanos_count_slaveintegerGLOBAL
Ndb_api_wait_scan_result_countintegerGLOBAL
Ndb_api_wait_scan_result_count_sessionintegerSESSION
Ndb_api_wait_scan_result_count_slaveintegerGLOBAL
Ndb_cluster_node_idintegerGLOBAL | SESSION
Ndb_config_from_hostintegerGLOBAL | SESSION
Ndb_config_from_portintegerGLOBAL | SESSION
Ndb_conflict_fn_epoch_transintegerGLOBAL
Ndb_conflict_fn_maxintegerGLOBAL
Ndb_conflict_fn_oldintegerGLOBAL
Ndb_conflict_trans_detect_iter_countintegerGLOBAL
Ndb_conflict_trans_row_reject_countintegerGLOBAL
Ndb_last_commit_epoch_serverintegerGLOBAL
Ndb_last_commit_epoch_sessionintegerSESSION
Ndb_cluster_node_idintegerGLOBAL
Ndb_number_of_data_nodesintegerGLOBAL
Ndb_pushed_queries_definedintegerGLOBAL
Ndb_pushed_queries_executedintegerGLOBAL
Ndb_scan_countintegerGLOBAL
Not_flushed_delayed_rowsintegerGLOBAL
Ongoing_anonymous_gtid_violating_transaction_countintegerGLOBAL
Ongoing_anonymous_transaction_countintegerGLOBAL
Ongoing_automatic_gtid_violating_transaction_countintegerGLOBAL
Open_filesintegerGLOBAL
Open_streamsintegerGLOBAL
Open_table_definitionsintegerGLOBAL
Open_tablesintegerGLOBAL | SESSION
Opened_filesintegerGLOBAL
Opened_table_definitionsintegerGLOBAL | SESSION
Opened_tablesintegerGLOBAL | SESSION
Performance_schema_accounts_lostintegerGLOBAL
Performance_schema_cond_classes_lostintegerGLOBAL
Performance_schema_cond_instances_lostintegerGLOBAL
Performance_schema_digest_lostintegerGLOBAL
Performance_schema_file_classes_lostintegerGLOBAL
Performance_schema_file_handles_lostintegerGLOBAL
Performance_schema_file_instances_lostintegerGLOBAL
Performance_schema_hosts_lostintegerGLOBAL
Performance_schema_index_stat_lostintegerGLOBAL
Performance_schema_locker_lostintegerGLOBAL
Performance_schema_memory_classes_lostintegerGLOBAL
Performance_schema_metadata_lock_lostintegerGLOBAL
Performance_schema_mutex_classes_lostintegerGLOBAL
Performance_schema_mutex_instances_lostintegerGLOBAL
Performance_schema_nested_statement_lostintegerGLOBAL
Performance_schema_prepared_statements_lostintegerGLOBAL
Performance_schema_program_lostintegerGLOBAL
Performance_schema_rwlock_classes_lostintegerGLOBAL
Performance_schema_rwlock_instances_lostintegerGLOBAL
Performance_schema_session_connect_attrs_lostintegerGLOBAL
Performance_schema_socket_classes_lostintegerGLOBAL
Performance_schema_socket_instances_lostintegerGLOBAL
Performance_schema_stage_classes_lostintegerGLOBAL
Performance_schema_statement_classes_lostintegerGLOBAL
Performance_schema_table_handles_lostintegerGLOBAL
Performance_schema_table_instances_lostintegerGLOBAL
Performance_schema_table_lock_stat_lostintegerGLOBAL
Performance_schema_thread_classes_lostintegerGLOBAL
Performance_schema_thread_instances_lostintegerGLOBAL
Performance_schema_users_lostintegerGLOBAL
Prepared_stmt_countintegerGLOBAL
Qcache_free_blocksintegerGLOBAL
Qcache_free_memoryintegerGLOBAL
Qcache_hitsintegerGLOBAL
Qcache_insertsintegerGLOBAL
Qcache_lowmem_prunesintegerGLOBAL
Qcache_not_cachedintegerGLOBAL
Qcache_queries_in_cacheintegerGLOBAL
Qcache_total_blocksintegerGLOBAL
QueriesintegerGLOBAL | SESSION
QuestionsintegerGLOBAL | SESSION
Rewriter_number_loaded_rulesintegerGLOBAL
Rewriter_number_reloadsintegerGLOBAL
Rewriter_number_rewritten_queriesintegerGLOBAL
Rewriter_reload_errorbooleanGLOBAL
Rpl_semi_sync_master_clientsintegerGLOBAL
Rpl_semi_sync_master_net_avg_wait_timeintegerGLOBAL
Rpl_semi_sync_master_net_wait_timeintegerGLOBAL
Rpl_semi_sync_master_net_waitsintegerGLOBAL
Rpl_semi_sync_master_no_timesintegerGLOBAL
Rpl_semi_sync_master_no_txintegerGLOBAL
Rpl_semi_sync_master_statusbooleanGLOBAL
Rpl_semi_sync_master_timefunc_failuresintegerGLOBAL
Rpl_semi_sync_master_tx_avg_wait_timeintegerGLOBAL
Rpl_semi_sync_master_tx_wait_timeintegerGLOBAL
Rpl_semi_sync_master_tx_waitsintegerGLOBAL
Rpl_semi_sync_master_wait_pos_backtraverseintegerGLOBAL
Rpl_semi_sync_master_wait_sessionsintegerGLOBAL
Rpl_semi_sync_master_yes_txintegerGLOBAL
Rpl_semi_sync_slave_statusbooleanGLOBAL
Rsa_public_keystringGLOBAL
Select_full_joinintegerGLOBAL | SESSION
Select_full_range_joinintegerGLOBAL | SESSION
Select_rangeintegerGLOBAL | SESSION
Select_range_checkintegerGLOBAL | SESSION
Select_scanintegerGLOBAL | SESSION
Slave_heartbeat_periodnumericGLOBAL
Slave_last_heartbeat GLOBAL
Slave_open_temp_tablesintegerGLOBAL
Slave_received_heartbeats GLOBAL
Slave_retried_transactionsintegerGLOBAL
Slave_runningbooleanGLOBAL
Slow_launch_threadsintegerGLOBAL | SESSION
Slow_queriesintegerGLOBAL | SESSION
Sort_merge_passesintegerGLOBAL | SESSION
Sort_rangeintegerGLOBAL | SESSION
Sort_rowsintegerGLOBAL | SESSION
Sort_scanintegerGLOBAL | SESSION
Ssl_accept_renegotiatesintegerGLOBAL
Ssl_acceptsintegerGLOBAL
Ssl_callback_cache_hitsintegerGLOBAL
Ssl_cipherstringGLOBAL | SESSION
Ssl_cipher_liststringGLOBAL | SESSION
Ssl_client_connectsintegerGLOBAL
Ssl_connect_renegotiatesintegerGLOBAL
Ssl_ctx_verify_depthintegerGLOBAL
Ssl_ctx_verify_modeintegerGLOBAL
Ssl_default_timeoutintegerGLOBAL | SESSION
Ssl_finished_acceptsintegerGLOBAL
Ssl_finished_connectsintegerGLOBAL
Ssl_server_not_afterintegerGLOBAL | SESSION
Ssl_server_not_beforeintegerGLOBAL | SESSION
Ssl_session_cache_hitsintegerGLOBAL
Ssl_session_cache_missesintegerGLOBAL
Ssl_session_cache_modestringGLOBAL
Ssl_session_cache_overflowsintegerGLOBAL
Ssl_session_cache_sizeintegerGLOBAL
Ssl_session_cache_timeoutsintegerGLOBAL
Ssl_sessions_reusedintegerGLOBAL | SESSION
Ssl_used_session_cache_entriesintegerGLOBAL
Ssl_verify_depthintegerGLOBAL | SESSION
Ssl_verify_modeintegerGLOBAL | SESSION
Ssl_versionstringGLOBAL | SESSION
Table_locks_immediateintegerGLOBAL
Table_locks_waitedintegerGLOBAL
Table_open_cache_hitsintegerGLOBAL | SESSION
Table_open_cache_missesintegerGLOBAL | SESSION
Table_open_cache_overflowsintegerGLOBAL | SESSION
Tc_log_max_pages_usedintegerGLOBAL
Tc_log_page_sizeintegerGLOBAL
Tc_log_page_waitsintegerGLOBAL
Threads_cachedintegerGLOBAL
Threads_connectedintegerGLOBAL
Threads_createdintegerGLOBAL
Threads_runningintegerGLOBAL
UptimeintegerGLOBAL
Uptime_since_flush_statusintegerGLOBAL
validate_password_dictionary_file_last_parseddatetimeGLOBAL
validate_password_dictionary_file_words_countintegerGLOBAL

The status variables have the meanings shown in the following list. For meanings of status variables specific to MySQL Cluster, see Section 21.3.3.8.3, “NDB Cluster Status Variables”.

6.1.8 Server SQL Modes

The MySQL server can operate in different SQL modes, and can apply these modes differently for different clients, depending on the value of the sql_mode system variable. DBAs can set the global SQL mode to match site server operating requirements, and each application can set its session SQL mode to its own requirements.

Modes affect the SQL syntax MySQL supports and the data validation checks it performs. This makes it easier to use MySQL in different environments and to use MySQL together with other database servers.

For answers to questions often asked about server SQL modes in MySQL, see Section A.3, “MySQL 5.7 FAQ: Server SQL Mode”.

When working with InnoDB tables, consider also the innodb_strict_mode system variable. It enables additional error checks for InnoDB tables.

Setting the SQL Mode

The default SQL mode in MySQL 5.7 includes these modes: ONLY_FULL_GROUP_BY, STRICT_TRANS_TABLES, NO_ZERO_IN_DATE, NO_ZERO_DATE, ERROR_FOR_DIVISION_BY_ZERO, NO_AUTO_CREATE_USER, and NO_ENGINE_SUBSTITUTION.

The ONLY_FULL_GROUP_BY and STRICT_TRANS_TABLES modes were added in MySQL 5.7.5. The NO_AUTO_CREATE_USER mode was added in MySQL 5.7.7. The ERROR_FOR_DIVISION_BY_ZERO, NO_ZERO_DATE, and NO_ZERO_IN_DATE modes were added in MySQL 5.7.8. For additional discussion regarding these changes to the default SQL mode value, see SQL Mode Changes in MySQL 5.7.

To set the SQL mode at server startup, use the --sql-mode="modes" option on the command line, or sql-mode="modes" in an option file such as my.cnf (Unix operating systems) or my.ini (Windows). modes is a list of different modes separated by commas. To clear the SQL mode explicitly, set it to an empty string using --sql-mode="" on the command line, or sql-mode="" in an option file.

Note

MySQL installation programs may configure the SQL mode during the installation process. For example, mysql_install_db creates a default option file named my.cnf in the base installation directory. This file contains a line that sets the SQL mode; see Section 5.4.2, “mysql_install_db — Initialize MySQL Data Directory”.

If the SQL mode differs from the default or from what you expect, check for a setting in an option file that the server reads at startup.

To change the SQL mode at runtime, set the global or session sql_mode system variable using a SET statement:

SET GLOBAL sql_mode = 'modes';
SET SESSION sql_mode = 'modes';

Setting the GLOBAL variable requires the SUPER privilege and affects the operation of all clients that connect from that time on. Setting the SESSION variable affects only the current client. Each client can change its session sql_mode value at any time.

To determine the current global or session sql_mode value, use the following statements:

SELECT @@GLOBAL.sql_mode;
SELECT @@SESSION.sql_mode;
Important

SQL mode and user-defined partitioning.  Changing the server SQL mode after creating and inserting data into partitioned tables can cause major changes in the behavior of such tables, and could lead to loss or corruption of data. It is strongly recommended that you never change the SQL mode once you have created tables employing user-defined partitioning.

When replicating partitioned tables, differing SQL modes on master and slave can also lead to problems. For best results, you should always use the same server SQL mode on the master and on the slave.

See Section 22.6, “Restrictions and Limitations on Partitioning”, for more information.

The Most Important SQL Modes

The most important sql_mode values are probably these:

  • ANSI

    This mode changes syntax and behavior to conform more closely to standard SQL. It is one of the special combination modes listed at the end of this section.

  • STRICT_TRANS_TABLES

    If a value could not be inserted as given into a transactional table, abort the statement. For a nontransactional table, abort the statement if the value occurs in a single-row statement or the first row of a multiple-row statement. More details are given later in this section.

    As of MySQL 5.7.5, the default SQL mode includes STRICT_TRANS_TABLES.

  • TRADITIONAL

    Make MySQL behave like a traditional SQL database system. A simple description of this mode is give an error instead of a warning when inserting an incorrect value into a column. It is one of the special combination modes listed at the end of this section.

    Note

    The INSERT or UPDATE aborts as soon as the error is noticed. This may not be what you want if you are using a nontransactional storage engine, because data changes made prior to the error may not be rolled back, resulting in a partially done update.

When this manual refers to strict mode, it means a mode with either or both STRICT_TRANS_TABLES or STRICT_ALL_TABLES enabled.

Full List of SQL Modes

The following list describes all supported SQL modes:

  • ALLOW_INVALID_DATES

    Do not perform full checking of dates. Check only that the month is in the range from 1 to 12 and the day is in the range from 1 to 31. This is very convenient for Web applications where you obtain year, month, and day in three different fields and you want to store exactly what the user inserted (without date validation). This mode applies to DATE and DATETIME columns. It does not apply TIMESTAMP columns, which always require a valid date.

    The server requires that month and day values be legal, and not merely in the range 1 to 12 and 1 to 31, respectively. With strict mode disabled, invalid dates such as '2004-04-31' are converted to '0000-00-00' and a warning is generated. With strict mode enabled, invalid dates generate an error. To permit such dates, enable ALLOW_INVALID_DATES.

  • ANSI_QUOTES

    Treat " as an identifier quote character (like the ` quote character) and not as a string quote character. You can still use ` to quote identifiers with this mode enabled. With ANSI_QUOTES enabled, you cannot use double quotation marks to quote literal strings, because it is interpreted as an identifier.

  • ERROR_FOR_DIVISION_BY_ZERO

    The ERROR_FOR_DIVISION_BY_ZERO mode affects handling of division by zero, which includes MOD(N,0). For data-change operations (INSERT, UPDATE), its effect also depends on whether strict SQL mode is enabled.

    • If this mode is not enabled, division by zero inserts NULL and produces no warning.

    • If this mode is enabled, division by zero inserts NULL and produces a warning.

    • If this mode and strict mode are enabled, division by zero produces an error, unless IGNORE is given as well. For INSERT IGNORE and UPDATE IGNORE, division by zero inserts NULL and produces a warning.

    For SELECT, division by zero returns NULL. Enabling ERROR_FOR_DIVISION_BY_ZERO causes a warning to be produced as well, regardless of whether strict mode is enabled.

    As of MySQL 5.7.4, ERROR_FOR_DIVISION_BY_ZERO is deprecated. In MySQL 5.7.4 through 5.7.7, ERROR_FOR_DIVISION_BY_ZERO does nothing when named explicitly. Instead, its effect is included in the effects of strict SQL mode. In MySQL 5.7.8 and later, ERROR_FOR_DIVISION_BY_ZERO does have an effect when named explicitly and is not part of strict mode, as before MySQL 5.7.4. However, it should be used in conjunction with strict mode and is enabled by default. A warning occurs if ERROR_FOR_DIVISION_BY_ZERO is enabled without also enabling strict mode or vice versa. For additional discussion, see SQL Mode Changes in MySQL 5.7.

    Because ERROR_FOR_DIVISION_BY_ZERO is deprecated, it will be removed in a future MySQL release as a separate mode name and its effect included in the effects of strict SQL mode.

  • HIGH_NOT_PRECEDENCE

    The precedence of the NOT operator is such that expressions such as NOT a BETWEEN b AND c are parsed as NOT (a BETWEEN b AND c). In some older versions of MySQL, the expression was parsed as (NOT a) BETWEEN b AND c. The old higher-precedence behavior can be obtained by enabling the HIGH_NOT_PRECEDENCE SQL mode.

    mysql> SET sql_mode = '';
    mysql> SELECT NOT 1 BETWEEN -5 AND 5;
            -> 0
    mysql> SET sql_mode = 'HIGH_NOT_PRECEDENCE';
    mysql> SELECT NOT 1 BETWEEN -5 AND 5;
            -> 1
    
  • IGNORE_SPACE

    Permit spaces between a function name and the ( character. This causes built-in function names to be treated as reserved words. As a result, identifiers that are the same as function names must be quoted as described in Section 10.2, “Schema Object Names”. For example, because there is a COUNT() function, the use of count as a table name in the following statement causes an error:

    mysql> CREATE TABLE count (i INT);
    ERROR 1064 (42000): You have an error in your SQL syntax
    

    The table name should be quoted:

    mysql> CREATE TABLE `count` (i INT);
    Query OK, 0 rows affected (0.00 sec)
    

    The IGNORE_SPACE SQL mode applies to built-in functions, not to user-defined functions or stored functions. It is always permissible to have spaces after a UDF or stored function name, regardless of whether IGNORE_SPACE is enabled.

    For further discussion of IGNORE_SPACE, see Section 10.2.4, “Function Name Parsing and Resolution”.

  • NO_AUTO_CREATE_USER

    Prevent the GRANT statement from automatically creating new user accounts if it would otherwise do so, unless authentication information is specified. The statement must specify a nonempty password using IDENTIFIED BY or an authentication plugin using IDENTIFIED WITH.

    It is preferable to create MySQL accounts with CREATE USER rather than GRANT. As of MySQL 5.7.6, NO_AUTO_CREATE_USER is deprecated. As of 5.7.7 the default SQL mode includes NO_AUTO_CREATE_USER and assignments to sql_mode that change the NO_AUTO_CREATE_USER mode state produce a warning, except assignments that set sql_mode to DEFAULT. NO_AUTO_CREATE_USER will be removed in a future MySQL release, at which point its effect will be enabled at all times (GRANT will not create accounts).

  • NO_AUTO_VALUE_ON_ZERO

    NO_AUTO_VALUE_ON_ZERO affects handling of AUTO_INCREMENT columns. Normally, you generate the next sequence number for the column by inserting either NULL or 0 into it. NO_AUTO_VALUE_ON_ZERO suppresses this behavior for 0 so that only NULL generates the next sequence number.

    This mode can be useful if 0 has been stored in a table's AUTO_INCREMENT column. (Storing 0 is not a recommended practice, by the way.) For example, if you dump the table with mysqldump and then reload it, MySQL normally generates new sequence numbers when it encounters the 0 values, resulting in a table with contents different from the one that was dumped. Enabling NO_AUTO_VALUE_ON_ZERO before reloading the dump file solves this problem. mysqldump now automatically includes in its output a statement that enables NO_AUTO_VALUE_ON_ZERO, to avoid this problem.

  • NO_BACKSLASH_ESCAPES

    Disable the use of the backslash character (\) as an escape character within strings. With this mode enabled, backslash becomes an ordinary character like any other.

  • NO_DIR_IN_CREATE

    When creating a table, ignore all INDEX DIRECTORY and DATA DIRECTORY directives. This option is useful on slave replication servers.

  • NO_ENGINE_SUBSTITUTION

    Control automatic substitution of the default storage engine when a statement such as CREATE TABLE or ALTER TABLE specifies a storage engine that is disabled or not compiled in.

    The default SQL mode includes NO_ENGINE_SUBSTITUTION.

    Because storage engines can be pluggable at runtime, unavailable engines are treated the same way:

    With NO_ENGINE_SUBSTITUTION disabled, for CREATE TABLE the default engine is used and a warning occurs if the desired engine is unavailable. For ALTER TABLE, a warning occurs and the table is not altered.

    With NO_ENGINE_SUBSTITUTION enabled, an error occurs and the table is not created or altered if the desired engine is unavailable.

  • NO_FIELD_OPTIONS

    Do not print MySQL-specific column options in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode.

  • NO_KEY_OPTIONS

    Do not print MySQL-specific index options in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode.

  • NO_TABLE_OPTIONS

    Do not print MySQL-specific table options (such as ENGINE) in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode.

  • NO_UNSIGNED_SUBTRACTION

    Subtraction between integer values, where one is of type UNSIGNED, produces an unsigned result by default. If the result would otherwise have been negative, an error results:

    mysql> SET sql_mode = '';
    Query OK, 0 rows affected (0.00 sec)
    
    mysql> SELECT CAST(0 AS UNSIGNED) - 1;
    ERROR 1690 (22003): BIGINT UNSIGNED value is out of range in '(cast(0 as unsigned) - 1)'
    

    If the NO_UNSIGNED_SUBTRACTION SQL mode is enabled, the result is negative:

    mysql> SET sql_mode = 'NO_UNSIGNED_SUBTRACTION';
    mysql> SELECT CAST(0 AS UNSIGNED) - 1;
    +-------------------------+
    | CAST(0 AS UNSIGNED) - 1 |
    +-------------------------+
    |                      -1 |
    +-------------------------+
    

    If the result of such an operation is used to update an UNSIGNED integer column, the result is clipped to the maximum value for the column type, or clipped to 0 if NO_UNSIGNED_SUBTRACTION is enabled. If strict SQL mode is enabled, an error occurs and the column remains unchanged.

    When NO_UNSIGNED_SUBTRACTION is enabled, the subtraction result is signed, even if any operand is unsigned. For example, compare the type of column c2 in table t1 with that of column c2 in table t2:

    
    mysql> SET sql_mode='';
    mysql> CREATE TABLE test (c1 BIGINT UNSIGNED NOT NULL);
    mysql> CREATE TABLE t1 SELECT c1 - 1 AS c2 FROM test;
    mysql> DESCRIBE t1;
    +-------+---------------------+------+-----+---------+-------+
    | Field | Type                | Null | Key | Default | Extra |
    +-------+---------------------+------+-----+---------+-------+
    | c2    | bigint(21) unsigned | NO   |     | 0       |       |
    +-------+---------------------+------+-----+---------+-------+
    
    mysql> SET sql_mode='NO_UNSIGNED_SUBTRACTION';
    mysql> CREATE TABLE t2 SELECT c1 - 1 AS c2 FROM test;
    mysql> DESCRIBE t2;
    +-------+------------+------+-----+---------+-------+
    | Field | Type       | Null | Key | Default | Extra |
    +-------+------------+------+-----+---------+-------+
    | c2    | bigint(21) | NO   |     | 0       |       |
    +-------+------------+------+-----+---------+-------+
    

    This means that BIGINT UNSIGNED is not 100% usable in all contexts. See Section 13.10, “Cast Functions and Operators”.

  • NO_ZERO_DATE

    The NO_ZERO_DATE mode affects whether the server permits '0000-00-00' as a valid date. Its effect also depends on whether strict SQL mode is enabled.

    • If this mode is not enabled, '0000-00-00' is permitted and inserts produce no warning.

    • If this mode is enabled, '0000-00-00' is permitted and inserts produce a warning.

    • If this mode and strict mode are enabled, '0000-00-00' is not permitted and inserts produce an error, unless IGNORE is given as well. For INSERT IGNORE and UPDATE IGNORE, '0000-00-00' is permitted and inserts produce a warning.

    As of MySQL 5.7.4, NO_ZERO_DATE is deprecated. In MySQL 5.7.4 through 5.7.7, NO_ZERO_DATE does nothing when named explicitly. Instead, its effect is included in the effects of strict SQL mode. In MySQL 5.7.8 and later, NO_ZERO_DATE does have an effect when named explicitly and is not part of strict mode, as before MySQL 5.7.4. However, it should be used in conjunction with strict mode and is enabled by default. A warning occurs if NO_ZERO_DATE is enabled without also enabling strict mode or vice versa. For additional discussion, see SQL Mode Changes in MySQL 5.7.

    Because NO_ZERO_DATE is deprecated, it will be removed in a future MySQL release as a separate mode name and its effect included in the effects of strict SQL mode.

  • NO_ZERO_IN_DATE

    The NO_ZERO_IN_DATE mode affects whether the server permits dates in which the year part is nonzero but the month or day part is 0. (This mode affects dates such as '2010-00-01' or '2010-01-00', but not '0000-00-00'. To control whether the server permits '0000-00-00', use the NO_ZERO_DATE mode.) The effect of NO_ZERO_IN_DATE also depends on whether strict SQL mode is enabled.

    • If this mode is not enabled, dates with zero parts are permitted and inserts produce no warning.

    • If this mode is enabled, dates with zero parts are inserted as '0000-00-00' and produce a warning.

    • If this mode and strict mode are enabled, dates with zero parts are not permitted and inserts produce an error, unless IGNORE is given as well. For INSERT IGNORE and UPDATE IGNORE, dates with zero parts are inserted as '0000-00-00' and produce a warning.

    As of MySQL 5.7.4, NO_ZERO_IN_DATE is deprecated. In MySQL 5.7.4 through 5.7.7, NO_ZERO_IN_DATE does nothing when named explicitly. Instead, its effect is included in the effects of strict SQL mode. In MySQL 5.7.8 and later, NO_ZERO_IN_DATE does have an effect when named explicitly and is not part of strict mode, as before MySQL 5.7.4. However, it should be used in conjunction with strict mode and is enabled by default. A warning occurs if NO_ZERO_IN_DATE is enabled without also enabling strict mode or vice versa. For additional discussion, see SQL Mode Changes in MySQL 5.7.

    Because NO_ZERO_IN_DATE is deprecated, it will be removed in a future MySQL release as a separate mode name and its effect included in the effects of strict SQL mode.

  • ONLY_FULL_GROUP_BY

    Reject queries for which the select list, HAVING condition, or ORDER BY list refer to nonaggregated columns that are neither named in the GROUP BY clause nor are functionally dependent on (uniquely determined by) GROUP BY columns.

    As of MySQL 5.7.5, the default SQL mode includes ONLY_FULL_GROUP_BY. (Before 5.7.5, MySQL does not detect functional dependency and ONLY_FULL_GROUP_BY is not enabled by default. For a description of pre-5.7.5 behavior, see the MySQL 5.6 Reference Manual.)

    A MySQL extension to standard SQL permits references in the HAVING clause to aliased expressions in the select list. Before MySQL 5.7.5, enabling ONLY_FULL_GROUP_BY disables this extension, thus requiring the HAVING clause to be written using unaliased expressions. As of MySQL 5.7.5, this restriction is lifted so that the HAVING clause can refer to aliases regardless of whether ONLY_FULL_GROUP_BY is enabled.

    For additional discussion and examples, see Section 13.19.3, “MySQL Handling of GROUP BY”.

  • PAD_CHAR_TO_FULL_LENGTH

    By default, trailing spaces are trimmed from CHAR column values on retrieval. If PAD_CHAR_TO_FULL_LENGTH is enabled, trimming does not occur and retrieved CHAR values are padded to their full length. This mode does not apply to VARCHAR columns, for which trailing spaces are retained on retrieval.

    
    mysql> CREATE TABLE t1 (c1 CHAR(10));
    Query OK, 0 rows affected (0.37 sec)
    
    mysql> INSERT INTO t1 (c1) VALUES('xy');
    Query OK, 1 row affected (0.01 sec)
    
    mysql> SET sql_mode = '';
    Query OK, 0 rows affected (0.00 sec)
    
    mysql> SELECT c1, CHAR_LENGTH(c1) FROM t1;
    +------+-----------------+
    | c1   | CHAR_LENGTH(c1) |
    +------+-----------------+
    | xy   |               2 |
    +------+-----------------+
    1 row in set (0.00 sec)
    
    mysql> SET sql_mode = 'PAD_CHAR_TO_FULL_LENGTH';
    Query OK, 0 rows affected (0.00 sec)
    
    mysql> SELECT c1, CHAR_LENGTH(c1) FROM t1;
    +------------+-----------------+
    | c1         | CHAR_LENGTH(c1) |
    +------------+-----------------+
    | xy         |              10 |
    +------------+-----------------+
    1 row in set (0.00 sec)
    
  • PIPES_AS_CONCAT

    Treat || as a string concatenation operator (same as CONCAT()) rather than as a synonym for OR.

  • REAL_AS_FLOAT

    Treat REAL as a synonym for FLOAT. By default, MySQL treats REAL as a synonym for DOUBLE.

  • STRICT_ALL_TABLES

    Enable strict SQL mode for all storage engines. Invalid data values are rejected. For details, see Strict SQL Mode.

    From MySQL 5.7.4 through 5.7.7, STRICT_ALL_TABLES includes the effect of the ERROR_FOR_DIVISION_BY_ZERO, NO_ZERO_DATE, and NO_ZERO_IN_DATE modes. For additional discussion, see SQL Mode Changes in MySQL 5.7.

  • STRICT_TRANS_TABLES

    Enable strict SQL mode for transactional storage engines, and when possible for nontransactional storage engines. For details, see Strict SQL Mode.

    From MySQL 5.7.4 through 5.7.7, STRICT_TRANS_TABLES includes the effect of the ERROR_FOR_DIVISION_BY_ZERO, NO_ZERO_DATE, and NO_ZERO_IN_DATE modes. For additional discussion, see SQL Mode Changes in MySQL 5.7.

Combination SQL Modes

The following special modes are provided as shorthand for combinations of mode values from the preceding list.

Strict SQL Mode

Strict mode controls how MySQL handles invalid or missing values in data-change statements such as INSERT or UPDATE. A value can be invalid for several reasons. For example, it might have the wrong data type for the column, or it might be out of range. A value is missing when a new row to be inserted does not contain a value for a non-NULL column that has no explicit DEFAULT clause in its definition. (For a NULL column, NULL is inserted if the value is missing.) Strict mode also affects DDL statements such as CREATE TABLE.

If strict mode is not in effect, MySQL inserts adjusted values for invalid or missing values and produces warnings (see Section 14.7.5.40, “SHOW WARNINGS Syntax”). In strict mode, you can produce this behavior by using INSERT IGNORE or UPDATE IGNORE.

For statements such as SELECT that do not change data, invalid values generate a warning in strict mode, not an error.

Strict mode produces an error for attempts to create a key that exceeds the maximum key length. When strict mode is not enabled, this results in a warning and truncation of the key to the maximum key length.

Strict mode does not affect whether foreign key constraints are checked. foreign_key_checks can be used for that. (See Section 6.1.5, “Server System Variables”.)

Strict SQL mode is in effect if either STRICT_ALL_TABLES or STRICT_TRANS_TABLES is enabled, although the effects of these modes differ somewhat:

  • For transactional tables, an error occurs for invalid or missing values in a data-change statement when either STRICT_ALL_TABLES or STRICT_TRANS_TABLES is enabled. The statement is aborted and rolled back.

  • For nontransactional tables, the behavior is the same for either mode if the bad value occurs in the first row to be inserted or updated: The statement is aborted and the table remains unchanged. If the statement inserts or modifies multiple rows and the bad value occurs in the second or later row, the result depends on which strict mode is enabled:

    • For STRICT_ALL_TABLES, MySQL returns an error and ignores the rest of the rows. However, because the earlier rows have been inserted or updated, the result is a partial update. To avoid this, use single-row statements, which can be aborted without changing the table.

    • For STRICT_TRANS_TABLES, MySQL converts an invalid value to the closest valid value for the column and inserts the adjusted value. If a value is missing, MySQL inserts the implicit default value for the column data type. In either case, MySQL generates a warning rather than an error and continues processing the statement. Implicit defaults are described in Section 12.7, “Data Type Default Values”.

Strict mode affects handling of division by zero, zero dates, and zeros in dates as follows:

  • Strict mode affects handling of division by zero, which includes MOD(N,0):

    For data-change operations (INSERT, UPDATE):

    • If strict mode is not enabled, division by zero inserts NULL and produces no warning.

    • If strict mode is enabled, division by zero produces an error, unless IGNORE is given as well. For INSERT IGNORE and UPDATE IGNORE, division by zero inserts NULL and produces a warning.

    For SELECT, division by zero returns NULL. Enabling strict mode causes a warning to be produced as well.

  • Strict mode affects whether the server permits '0000-00-00' as a valid date:

    • If strict mode is not enabled, '0000-00-00' is permitted and inserts produce no warning.

    • If strict mode is enabled, '0000-00-00' is not permitted and inserts produce an error, unless IGNORE is given as well. For INSERT IGNORE and UPDATE IGNORE, '0000-00-00' is permitted and inserts produce a warning.

  • Strict mode affects whether the server permits dates in which the year part is nonzero but the month or day part is 0 (dates such as '2010-00-01' or '2010-01-00'):

    • If strict mode is not enabled, dates with zero parts are permitted and inserts produce no warning.

    • If strict mode is enabled, dates with zero parts are not permitted and inserts produce an error, unless IGNORE is given as well. For INSERT IGNORE and UPDATE IGNORE, dates with zero parts are inserted as '0000-00-00' (which is considered valid with IGNORE) and produce a warning.

For more information about strict mode with respect to IGNORE, see Comparison of the IGNORE Keyword and Strict SQL Mode.

Before MySQL 5.7.4, and in MySQL 5.7.8 and later, strict mode affects handling of division by zero, zero dates, and zeros in dates in conjunction with the ERROR_FOR_DIVISION_BY_ZERO, NO_ZERO_DATE, and NO_ZERO_IN_DATE modes. From MySQL 5.7.4 though 5.7.7, the ERROR_FOR_DIVISION_BY_ZERO, NO_ZERO_DATE, and NO_ZERO_IN_DATE modes do nothing when named explicitly and their effects are included in the effects of strict mode. For additional discussion, see SQL Mode Changes in MySQL 5.7.

Comparison of the IGNORE Keyword and Strict SQL Mode

This section compares the effect on statement execution of the IGNORE keyword (which downgrades errors to warnings) and strict SQL mode (which upgrades warnings to errors). It describes which statements they affect, and which errors they apply to.

The following table presents a summary comparison of statement behavior when the default is to produce an error versus a warning. An example of when the default is to produce an error is inserting a NULL into a NOT NULL column. An example of when the default is to produce a warning is inserting a value of the wrong data type into a column (such as inserting the string 'abc' into an integer column).

Operational ModeWhen Statement Default is ErrorWhen Statement Default is Warning
Without IGNORE or strict SQL modeErrorWarning
With IGNOREWarningWarning (same as without IGNORE or strict SQL mode)
With strict SQL modeError (same as without IGNORE or strict SQL mode)Error
With IGNORE and strict SQL modeWarningWarning

One conclusion to draw from the table is that when the IGNORE keyword and strict SQL mode are both in effect, IGNORE takes precedence. This means that, although IGNORE and strict SQL mode can be considered to have opposite effects on error handling, they do not cancel when used together.

The Effect of IGNORE on Statement Execution

Several statements in MySQL support an optional IGNORE keyword. This keyword causes the server to downgrade certain types of errors and generate warnings instead. For a multiple-row statement, IGNORE causes the statement to skip to the next row instead of aborting.

For example, if the table t has a primary key column i, attempting to insert the same value of i into multiple rows normally produces a duplicate-key error:

mysql> INSERT INTO t (i) VALUES(1),(1);
ERROR 1062 (23000): Duplicate entry '1' for key 'PRIMARY'

With IGNORE, the row containing the duplicate key still is not inserted, but a warning occurs instead of an error:


mysql> INSERT IGNORE INTO t (i) VALUES(1),(1);
Query OK, 1 row affected, 1 warning (0.01 sec)
Records: 2  Duplicates: 1  Warnings: 1

mysql> SHOW WARNINGS;
+---------+------+---------------------------------------+
| Level   | Code | Message                               |
+---------+------+---------------------------------------+
| Warning | 1062 | Duplicate entry '1' for key 'PRIMARY' |
+---------+------+---------------------------------------+
1 row in set (0.00 sec)

These statements support the IGNORE keyword:

  • CREATE TABLE ... SELECT: IGNORE does not apply to the CREATE TABLE or SELECT parts of the statement but to inserts into the table of rows produced by the SELECT. Rows that duplicate an existing row on a unique key value are discarded.

  • DELETE: IGNORE causes MySQL to ignore errors during the process of deleting rows.

  • INSERT: With IGNORE, rows that duplicate an existing row on a unique key value are discarded. Rows set to values that would cause data conversion errors are set to the closest valid values instead.

    For partitioned tables where no partition matching a given value is found, IGNORE causes the insert operation to fail silently for rows containing the unmatched value.

  • LOAD DATA, LOAD XML: With IGNORE, rows that duplicate an existing row on a unique key value are discarded.

  • UPDATE: With IGNORE, rows for which duplicate-key conflicts occur on a unique key value are not updated. Rows updated to values that would cause data conversion errors are updated to the closest valid values instead.

The IGNORE keyword applies to the following errors:

ER_BAD_NULL_ERROR
ER_DUP_ENTRY
ER_DUP_ENTRY_WITH_KEY_NAME
ER_DUP_KEY
ER_NO_PARTITION_FOR_GIVEN_VALUE
ER_NO_PARTITION_FOR_GIVEN_VALUE_SILENT
ER_NO_REFERENCED_ROW_2
ER_ROW_DOES_NOT_MATCH_GIVEN_PARTITION_SET
ER_ROW_IS_REFERENCED_2
ER_SUBQUERY_NO_1_ROW
ER_VIEW_CHECK_FAILED
The Effect of Strict SQL Mode on Statement Execution

The MySQL server can operate in different SQL modes, and can apply these modes differently for different clients, depending on the value of the sql_mode system variable. In strict SQL mode, the server upgrades certain warnings to errors.

For example, in non-strict SQL mode, inserting the string 'abc' into an integer column results in conversion of the value to 0 and a warning:

mysql> SET sql_mode = '';
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO t (i) VALUES('abc');
Query OK, 1 row affected, 1 warning (0.01 sec)

mysql> SHOW WARNINGS;
+---------+------+--------------------------------------------------------+
| Level   | Code | Message                                                |
+---------+------+--------------------------------------------------------+
| Warning | 1366 | Incorrect integer value: 'abc' for column 'i' at row 1 |
+---------+------+--------------------------------------------------------+
1 row in set (0.00 sec)

In strict SQL mode, the invalid value is rejected with an error:

mysql> SET sql_mode = 'STRICT_ALL_TABLES';
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO t (i) VALUES('abc');
ERROR 1366 (HY000): Incorrect integer value: 'abc' for column 'i' at row 1

For more information about possible settings of the sql_mode system variable, see Section 6.1.8, “Server SQL Modes”.

Strict SQL mode applies to the following statements under conditions for which some value might be out of range or an invalid row is inserted into or deleted from a table:

Within stored programs, individual statements of the types just listed execute in strict SQL mode if the program was defined while strict mode was in effect.

Strict SQL mode applies to the following errors, represent a class of errors in which an input value is either invalid or missing. A value is invalid if it has the wrong data type for the column or might be out of range. A value is missing if a new row to be inserted does not contain a value for a NOT NULL column that has no explicit DEFAULT clause in its definition.

ER_BAD_NULL_ERROR
ER_CUT_VALUE_GROUP_CONCAT
ER_DATA_TOO_LONG
ER_DATETIME_FUNCTION_OVERFLOW
ER_DIVISION_BY_ZERO
ER_INVALID_ARGUMENT_FOR_LOGARITHM
ER_NO_DEFAULT_FOR_FIELD
ER_NO_DEFAULT_FOR_VIEW_FIELD
ER_TOO_LONG_KEY
ER_TRUNCATED_WRONG_VALUE
ER_TRUNCATED_WRONG_VALUE_FOR_FIELD
ER_WARN_DATA_OUT_OF_RANGE
ER_WARN_NULL_TO_NOTNULL
ER_WARN_TOO_FEW_RECORDS
ER_WRONG_ARGUMENTS
ER_WRONG_VALUE_FOR_TYPE
WARN_DATA_TRUNCATED

SQL Mode Changes in MySQL 5.7

In MySQL 5.7.5, the ONLY_FULL_GROUP_BY SQL mode is enabled by default because GROUP BY processing has become more sophisticated to include detection of functional dependencies. However, if you find that having ONLY_FULL_GROUP_BY enabled causes queries for existing applications to be rejected, either of these actions should restore operation:

  • If it is possible to modify an offending query, do so, either so that nonaggregated columns are functionally dependent on GROUP BY columns, or by referring to nonaggregated columns using ANY_VALUE().

  • If it is not possible to modify an offending query (for example, if it is generated by a third-party application), set the sql_mode system variable at server startup to not enable ONLY_FULL_GROUP_BY.

As of MySQL 5.7.4, the ERROR_FOR_DIVISION_BY_ZERO, NO_ZERO_DATE, and NO_ZERO_IN_DATE SQL modes are deprecated. From MySQL 5.7.4 though 5.7.7, these modes do nothing when named explicitly. Instead, their effects are included in the effects of strict SQL mode (STRICT_ALL_TABLES or STRICT_TRANS_TABLES). In other words, strict mode means the same thing in those versions as the pre-5.7.4 meaning of strict mode plus ERROR_FOR_DIVISION_BY_ZERO, NO_ZERO_DATE, and NO_ZERO_IN_DATE.

The MySQL 5.7.4 change to make strict mode more strict by including ERROR_FOR_DIVISION_BY_ZERO, NO_ZERO_DATE, and NO_ZERO_IN_DATE caused some problems. For example, in MySQL 5.6 with strict mode but not NO_ZERO_DATE enabled, TIMESTAMP columns can be defined with DEFAULT '0000-00-00 00:00:00'. In MySQL 5.7.4 with the same mode settings, strict mode includes the effect of NO_ZERO_DATE and TIMESTAMP columns cannot be defined with DEFAULT '0000-00-00 00:00:00'. This causes replication of CREATE TABLE statements from 5.6 to 5.7.4 to fail if they contain such TIMESTAMP columns.

The long term plan is still to have the three affected modes be included in strict SQL mode and to remove them as explicit modes in a future MySQL release. But to restore compatibility in MySQL 5.7 with MySQL 5.6 strict mode and to provide additional time for affected applications to be modified, the following changes were made in MySQL 5.7.8:

With the preceding changes, stricter data checking is still enabled by default, but the individual modes can be disabled in environments where it is currently desirable or necessary to do so.

Although in MySQL 5.7.8 and later ERROR_FOR_DIVISION_BY_ZERO, NO_ZERO_DATE, and NO_ZERO_IN_DATE can be used separately from strict mode, it is intended that they be used together. As a reminder, a warning occurs if they are enabled without also enabling strict mode or vice versa.

Important

The following discussion applies only for MySQL versions 5.7.4 through 5.7.7. For upgrades from a version older than MySQL 5.7.4, we recommend upgrading to MySQL 5.7.8 or later, which renders this discussion unnecessary.

The remainder of this section describes the SQL mode settings to use in MySQL 5.7.4 through 5.7.7 to achieve the same statement execution as before 5.7.4, including the cases for INSERT and UPDATE in which IGNORE is given. It also provides guidelines for determining whether applications need modification to behave the same before and after the SQL mode changes.

The following table shows how to control handling of division by zero for versions other than MySQL 5.7.4 through 5.7.7 and for MySQL 5.7.4 through 5.7.7.

Desired BehaviorMySQL 5.7.x Versions Except 5.7.4 Through 5.7.7MySQL 5.7.4 Through 5.7.7
insert NULL, produce no warningERROR_FOR_DIVISION_BY_ZERO not enabledstrict mode not enabled
insert NULL, produce warningERROR_FOR_DIVISION_BY_ZERO, or ERROR_FOR_DIVISION_BY_ZERO + strict mode + IGNOREstrict mode + IGNORE
errorERROR_FOR_DIVISION_BY_ZERO + strict modestrict mode

The following table shows how to control whether the server permits '0000-00-00' as a valid date for versions other than MySQL 5.7.4 through 5.7.7 and for MySQL 5.7.4 through 5.7.7.

Desired BehaviorMySQL 5.7.x Versions Except 5.7.4 Through 5.7.7MySQL 5.7.4 Through 5.7.7
insert '0000-00-00', produce no warningNO_ZERO_DATE not enabledstrict mode not enabled
insert '0000-00-00', produce warningNO_ZERO_DATE, or NO_ZERO_DATE + strict mode + IGNOREstrict mode + IGNORE
errorNO_ZERO_DATE + strict modestrict mode

The following table shows how to control whether the server permits dates with zero parts for versions other than MySQL 5.7.4 through 5.7.7 and for MySQL 5.7.4 through 5.7.7.

Desired BehaviorMySQL 5.7.x Versions Except 5.7.4 Through 5.7.7MySQL 5.7.4 Through 5.7.7
insert date, produce no warningNO_ZERO_IN_DATE not enabledstrict mode not enabled
insert '0000-00-00', produce warningNO_ZERO_IN_DATE, or NO_ZERO_IN_DATE + strict mode + IGNOREstrict mode + IGNORE
errorNO_ZERO_IN_DATE + strict modestrict mode

The following discussion describes the conditions under which a given statement produces the same or different result under the SQL mode changes in MySQL 5.7.4 through 5.7.7. It considers only strict mode (STRICT_ALL_TABLES or STRICT_TRANS_TABLES) and the three deprecated modes (ERROR_FOR_DIVISION_BY_ZERO, NO_ZERO_DATE, and NO_ZERO_IN_DATE). Other SQL modes such as ANSI_QUOTES or ONLY_FULL_GROUP_BY are assumed to be held constant before and after an upgrade.

This discussion also describes how to prepare for an upgrade to 5.7.4 through 5.7.7 from a version older than 5.7.4. Any modifications should be made before upgrading.

There is no change in behavior between MySQL 5.6 and 5.7 for the following SQL mode settings. A statement that executes under one of these settings needs no modification to produce the same result in 5.6 and 5.7:

  • Strict mode and the three deprecated modes are all not enabled.

  • Strict mode and the three deprecated modes are all enabled.

A change from warnings in MySQL 5.6 to no warnings in MySQL 5.7 occurs for the following SQL mode settings. The result of statement execution is the same in 5.6 and 5.7, so statements need no modification unless warnings are considered significant:

A behavior change occurs under the following SQL mode settings. A statement that executes under one of these settings must be modified to produce the same result in 5.6 and 5.7:

  • Strict mode is not enabled, NO_ZERO_IN_DATE is enabled. For this mode setting, expect these differences in statement execution:

    • In 5.6, the server inserts dates with zero parts as '0000-00-00' and produces a warning.

    • In 5.7, the server inserts dates with zero parts as is and produces no warning.

  • Strict mode is enabled, with some but not all of the three deprecated modes enabled. For this mode setting, expect these differences in statement execution:

    Statements that would be affected by enabling the not-enabled deprecated modes produce errors in 5.7 but not in 5.6. Suppose that strict mode, NO_ZERO_DATE, and NO_ZERO_IN_DATE are enabled, and a data-change statement performs division by zero:

To prepare for an upgrade to MySQL 5.7.4 through 5.7.7, the main principle is to make sure that your applications will operate the same way in MySQL 5.6 and 5.7. For example, you can adopt either of these approaches to application compatibility:

  • Modify the application to set the SQL mode on a version-specific basis. If we assume that an application will not be used with development versions of MySQL 5.7 prior to 5.7.4, it is possible to set the sql_mode value for the application based on the current server version as follows:

    SET sql_mode = IF(LEFT(VERSION(),3)<'5.7',5.6 mode,5.7 mode);
    

    The tables shown earlier in this section serve as a guide to the appropriate equivalent modes for MySQL 5.6 and 5.7.

  • Modify the application to execute under an SQL mode for which statements produce the same result in MySQL 5.6 and 5.7.

    Tip

    TRADITIONAL SQL mode in MySQL 5.6 includes strict mode and the three deprecated modes. If you write applications to operate in TRADITIONAL mode in MySQL 5.6, there is no change to make for MySQL 5.7.

When assessing SQL mode compatibility between MySQL 5.6 and 5.7, consider particularly these statement execution contexts:

  • Replication. You will encounter replication incompatibility related to the SQL mode changes under the following conditions:

    • MySQL 5.6 master and 5.7 slave

    • Statement-based replication

    • An SQL mode setting for which statements produce different results in MySQL 5.6 and 5.7, as described earlier

    To handle this incompatibility, use one of these workarounds:

    • Use row-based replication

    • Use IGNORE

    • Use an SQL mode for which statements do not produce different results in MySQL 5.6 and 5.7

  • Stored programs (stored procedures and functions, triggers, and events). Each stored program executes using the SQL mode in effect at the time it was created. To identify stored programs that may be affected by differences between MySQL 5.6 and 5.7 in SQL mode handling, use these queries:

    SELECT ROUTINE_SCHEMA, ROUTINE_NAME, ROUTINE_TYPE, SQL_MODE
    FROM INFORMATION_SCHEMA.ROUTINES
    WHERE SQL_MODE LIKE '%STRICT%'
    OR SQL_MODE LIKE '%DIVISION%'
    OR SQL_MODE LIKE '%NO_ZERO%';
    
    SELECT TRIGGER_SCHEMA, TRIGGER_NAME, SQL_MODE
    FROM INFORMATION_SCHEMA.TRIGGERS
    WHERE SQL_MODE LIKE '%STRICT%'
    OR SQL_MODE LIKE '%DIVISION%'
    OR SQL_MODE LIKE '%NO_ZERO%';
    
    SELECT EVENT_SCHEMA, EVENT_NAME, SQL_MODE
    FROM INFORMATION_SCHEMA.EVENTS
    WHERE SQL_MODE LIKE '%STRICT%'
    OR SQL_MODE LIKE '%DIVISION%'
    OR SQL_MODE LIKE '%NO_ZERO%';
    

6.1.9 IPv6 Support

Support for IPv6 in MySQL includes these capabilities:

The following sections describe how to set up MySQL so that clients can connect to the server over IPv6.

6.1.9.1 Verifying System Support for IPv6

Before MySQL Server can accept IPv6 connections, the operating system on your server host must support IPv6. As a simple test to determine whether that is true, try this command:

shell> ping6 ::1
16 bytes from ::1, icmp_seq=0 hlim=64 time=0.171 ms
16 bytes from ::1, icmp_seq=1 hlim=64 time=0.077 ms
...

To produce a description of your system's network interfaces, invoke ifconfig -a and look for IPv6 addresses in the output.

If your host does not support IPv6, consult your system documentation for instructions on enabling it. It might be that you need only reconfigure an existing network interface to add an IPv6 address. Or a more extensive change might be needed, such as rebuilding the kernel with IPv6 options enabled.

These links may be helpful in setting up IPv6 on various platforms:

6.1.9.2 Configuring the MySQL Server to Permit IPv6 Connections

The MySQL server listens on a single network socket for TCP/IP connections. This socket is bound to a single address, but it is possible for an address to map onto multiple network interfaces. To specify an address, use the --bind-address=addr option at server startup, where addr is an IPv4 or IPv6 address or a host name. (IPv6 addresses are not supported before MySQL 5.5.3.) If addr is a host name, the server resolves the name to an IP address and binds to that address.

The server treats different types of addresses as follows:

  • If the address is *, the server accepts TCP/IP connections on all server host IPv6 and IPv4 interfaces if the server host supports IPv6, or accepts TCP/IP connections on all IPv4 addresses otherwise. Use this address to permit both IPv4 and IPv6 connections on all server interfaces. This value is the default.

  • If the address is 0.0.0.0, the server accepts TCP/IP connections on all server host IPv4 interfaces.

  • If the address is ::, the server accepts TCP/IP connections on all server host IPv4 and IPv6 interfaces. Use this address to permit both IPv4 and IPv6 connections on all server interfaces.

  • If the address is an IPv4-mapped address, the server accepts TCP/IP connections for that address, in either IPv4 or IPv6 format. For example, if the server is bound to ::ffff:127.0.0.1, clients can connect using --host=127.0.0.1 or --host=::ffff:127.0.0.1.

  • If the address is a regular IPv4 or IPv6 address (such as 127.0.0.1 or ::1), the server accepts TCP/IP connections only for that IPv4 or IPv6 address.

If you intend to bind the server to a specific address, be sure that the mysql.user grant table contains an account with administrative privileges that you can use to connect to that address. Otherwise, you will not be able to shut down the server. For example, if you bind the server to *, you can connect to it using all existing accounts. But if you bind the server to ::1, it accepts connections only on that address. In that case, first make sure that the 'root'@'::1' account is present in the mysql.user table so you can still connect to the server to shut it down.

6.1.9.3 Connecting Using the IPv6 Local Host Address

The following procedure shows how to configure MySQL to permit IPv6 connections by clients that connect to the local server using the ::1 local host address. The instructions given here assume that your system supports IPv6.

  1. Start the MySQL server with an appropriate --bind-address option to permit it to accept IPv6 connections. For example, put the following lines in your server option file and restart the server:

    [mysqld]
    bind-address = *
    

    Alternatively, you can bind the server to ::1, but that makes the server more restrictive for TCP/IP connections. It accepts only IPv6 connections for that single address and rejects IPv4 connections. For more information, see Section 6.1.9.2, “Configuring the MySQL Server to Permit IPv6 Connections”.

  2. As an administrator, connect to the server and create an account for a local user who will connect from the ::1 local IPv6 host address:

    mysql> CREATE USER 'ipv6user'@'::1' IDENTIFIED BY 'ipv6pass';
    

    For the permitted syntax of IPv6 addresses in account names, see Section 7.2.3, “Specifying Account Names”. In addition to the CREATE USER statement, you can issue GRANT statements that give specific privileges to the account, although that is not necessary for the remaining steps in this procedure.

  3. Invoke the mysql client to connect to the server using the new account:

    shell> mysql -h ::1 -u ipv6user -pipv6pass
    
  4. Try some simple statements that show connection information:

    mysql> STATUS
    ...
    Connection:   ::1 via TCP/IP
    ...
    
    mysql> SELECT CURRENT_USER(), @@bind_address;
    +----------------+----------------+
    | CURRENT_USER() | @@bind_address |
    +----------------+----------------+
    | ipv6user@::1   | ::             |
    +----------------+----------------+
    

6.1.9.4 Connecting Using IPv6 Nonlocal Host Addresses

The following procedure shows how to configure MySQL to permit IPv6 connections by remote clients. It is similar to the preceding procedure for local clients, but the server and client hosts are distinct and each has its own nonlocal IPv6 address. The example uses these addresses:

Server host: 2001:db8:0:f101::1
Client host: 2001:db8:0:f101::2

These addresses are chosen from the nonroutable address range recommended by IANA for documentation purposes and suffice for testing on your local network. To accept IPv6 connections from clients outside the local network, the server host must have a public address. If your network provider assigns you an IPv6 address, you can use that. Otherwise, another way to obtain an address is to use an IPv6 broker; see Section 6.1.9.5, “Obtaining an IPv6 Address from a Broker”.

  1. Start the MySQL server with an appropriate --bind-address option to permit it to accept IPv6 connections. For example, put the following lines in your server option file and restart the server:

    [mysqld]
    bind-address = *
    

    Alternatively, you can bind the server to 2001:db8:0:f101::1, but that makes the server more restrictive for TCP/IP connections. It accepts only IPv6 connections for that single address and rejects IPv4 connections. For more information, see Section 6.1.9.2, “Configuring the MySQL Server to Permit IPv6 Connections”.

  2. On the server host (2001:db8:0:f101::1), create an account for a user who will connect from the client host (2001:db8:0:f101::2):

    mysql> CREATE USER 'remoteipv6user'@'2001:db8:0:f101::2' IDENTIFIED BY 'remoteipv6pass';
    
  3. On the client host (2001:db8:0:f101::2), invoke the mysql client to connect to the server using the new account:

    shell> mysql -h 2001:db8:0:f101::1 -u remoteipv6user -premoteipv6pass
    
  4. Try some simple statements that show connection information:

    mysql> STATUS
    ...
    Connection:   2001:db8:0:f101::1 via TCP/IP
    ...
    
    mysql> SELECT CURRENT_USER(), @@bind_address;
    +-----------------------------------+----------------+
    | CURRENT_USER()                    | @@bind_address |
    +-----------------------------------+----------------+
    | remoteipv6user@2001:db8:0:f101::2 | ::             |
    +-----------------------------------+----------------+
    

6.1.9.5 Obtaining an IPv6 Address from a Broker

If you do not have a public IPv6 address that enables your system to communicate over IPv6 outside your local network, you can obtain one from an IPv6 broker. The Wikipedia IPv6 Tunnel Broker page lists several brokers and their features, such as whether they provide static addresses and the supported routing protocols.

After configuring your server host to use a broker-supplied IPv6 address, start the MySQL server with an appropriate --bind-address option to permit the server to accept IPv6 connections. For example, put the following lines in the server option file and restart the server:

[mysqld]
bind-address = *

Alternatively, you can bind the server to the specific IPv6 address provided by the broker, but that makes the server more restrictive for TCP/IP connections. It accepts only IPv6 connections for that single address and rejects IPv4 connections. For more information, see Section 6.1.9.2, “Configuring the MySQL Server to Permit IPv6 Connections”. In addition, if the broker allocates dynamic addresses, the address provided for your system might change the next time you connect to the broker. If so, any accounts you create that name the original address become invalid. To bind to a specific address but avoid this change-of-address problem, you may be able to arrange with the broker for a static IPv6 address.

The following example shows how to use Freenet6 as the broker and the gogoc IPv6 client package on Gentoo Linux.

  1. Create an account at Freenet6 by visiting this URL and signing up:

    http://gogonet.gogo6.com
    
  2. After creating the account, go to this URL, sign in, and create a user ID and password for the IPv6 broker:

    http://gogonet.gogo6.com/page/freenet6-registration
    

  3. As root, install gogoc:

    shell> emerge gogoc
    
  4. Edit /etc/gogoc/gogoc.conf to set the userid and password values. For example:

    userid=gogouser
    passwd=gogopass
    
  5. Start gogoc:

    shell> /etc/init.d/gogoc start
    

    To start gogoc each time your system boots, execute this command:

    shell> rc-update add gogoc default
    
  6. Use ping6 to try to ping a host:

    shell> ping6 ipv6.google.com
    
  7. To see your IPv6 address:

    shell> ifconfig tun
    

6.1.10 Server-Side Help

MySQL Server supports a HELP statement that returns information from the MySQL Reference manual (see Section 14.8.3, “HELP Syntax”). Several tables in the mysql system database contain the information needed to support this statement (see Section 6.3, “The mysql System Database”). The proper operation of this statement requires that these help tables be initialized, which is done by processing the contents of the fill_help_tables.sql script.

If you install MySQL using a binary or source distribution on Unix, help table content initialization occurs when you initialize the data directory (see Section 2.10.1, “Initializing the Data Directory”). For an RPM distribution on Linux or binary distribution on Windows, content initialization occurs as part of the MySQL installation process.

If you upgrade MySQL using a binary distribution, help table content is not upgraded automatically, but you can upgrade it manually. Locate the fill_help_tables.sql file in the share or share/mysql directory. Change location into that directory and process the file with the mysql client as follows:

shell> mysql -u root mysql < fill_help_tables.sql

You can also obtain the latest fill_help_tables.sql at any time to upgrade your help tables. Download the proper file for your version of MySQL from http://dev.mysql.com/doc/index-other.html. After downloading and uncompressing the file, process it with mysql as described previously.

If you are working with Git and a MySQL development source tree, you must use a downloaded copy of the fill_help_tables.sql file because the source tree contains only a stub version.

Note

For a server that participates in replication, the help table content upgrade process involves multiple servers. For details, see Section 18.4.1.29, “Replication of Server-Side Help Tables”.

6.1.11 Server Response to Signals

On Unix, signals can be sent to processes. mysqld responds to signals sent to it as follows:

  • SIGTERM causes the server to shut down.

  • SIGHUP causes the server to reload the grant tables and to flush tables, logs, the thread cache, and the host cache. These actions are like various forms of the FLUSH statement. The server also writes a status report to the error log that has this format:

    Status information:
    
    Current dir: /var/mysql/data/
    Running threads: 0  Stack size: 196608
    Current locks:
    
    Key caches:
    default
    Buffer_size:       8388600
    Block_size:           1024
    Division_limit:        100
    Age_limit:             300
    blocks used:             0
    not flushed:             0
    w_requests:              0
    writes:                  0
    r_requests:              0
    reads:                   0
    
    handler status:
    read_key:            0
    read_next:           0
    read_rnd             0
    read_first:          1
    write:               0
    delete               0
    update:              0
    
    Table status:
    Opened tables:          5
    Open tables:            0
    Open files:             7
    Open streams:           0
    
    Alarm status:
    Active alarms:   1
    Max used alarms: 2
    Next alarm time: 67
    

6.1.12 The Server Shutdown Process

The server shutdown process takes place as follows:

  1. The shutdown process is initiated.

    This can occur initiated several ways. For example, a user with the SHUTDOWN privilege can execute a mysqladmin shutdown command. mysqladmin can be used on any platform supported by MySQL. Other operating system-specific shutdown initiation methods are possible as well: The server shuts down on Unix when it receives a SIGTERM signal. A server running as a service on Windows shuts down when the services manager tells it to.

  2. The server creates a shutdown thread if necessary.

    Depending on how shutdown was initiated, the server might create a thread to handle the shutdown process. If shutdown was requested by a client, a shutdown thread is created. If shutdown is the result of receiving a SIGTERM signal, the signal thread might handle shutdown itself, or it might create a separate thread to do so. If the server tries to create a shutdown thread and cannot (for example, if memory is exhausted), it issues a diagnostic message that appears in the error log:

    Error: Can't create thread to kill server
    
  3. The server stops accepting new connections.

    To prevent new activity from being initiated during shutdown, the server stops accepting new client connections by closing the handlers for the network interfaces to which it normally listens for connections: the TCP/IP port, the Unix socket file, the Windows named pipe, and shared memory on Windows.

  4. The server terminates current activity.

    For each thread associated with a client connection, the server breaks the connection to the client and marks the thread as killed. Threads die when they notice that they are so marked. Threads for idle connections die quickly. Threads that currently are processing statements check their state periodically and take longer to die. For additional information about thread termination, see Section 14.7.6.4, “KILL Syntax”, in particular for the instructions about killed REPAIR TABLE or OPTIMIZE TABLE operations on MyISAM tables.

    For threads that have an open transaction, the transaction is rolled back. If a thread is updating a nontransactional table, an operation such as a multiple-row UPDATE or INSERT may leave the table partially updated because the operation can terminate before completion.

    If the server is a master replication server, it treats threads associated with currently connected slaves like other client threads. That is, each one is marked as killed and exits when it next checks its state.

    If the server is a slave replication server, it stops the I/O and SQL threads, if they are active, before marking client threads as killed. The SQL thread is permitted to finish its current statement (to avoid causing replication problems), and then stops. If the SQL thread is in the middle of a transaction at this point, the server waits until the current replication event group (if any) has finished executing, or until the user issues a KILL QUERY or KILL CONNECTION statement. See also Section 14.4.2.7, “STOP SLAVE Syntax”. Since nontransactional statements cannot be rolled back, in order to guarantee crash-safe replication, only transactional tables should be used.

    Note

    To guarantee crash safety on the slave, you must run the slave with --relay-log-recovery enabled.

    See also Section 18.2.4, “Replication Relay and Status Logs”).

  5. The server shuts down or closes storage engines.

    At this stage, the server flushes the table cache and closes all open tables.

    Each storage engine performs any actions necessary for tables that it manages. InnoDB flushes its buffer pool to disk (unless innodb_fast_shutdown is 2), writes the current LSN to the tablespace, and terminates its own internal threads. MyISAM flushes any pending index writes for a table.

  6. The server exits.

To provide information to management processes, the server returns one of the exit codes described in the following list. The phrase in parentheses indicates the action taken by systemd in response to the code, for platforms on which systemd is used to manage the server.

  • 0 = successful termination (no restart done)

  • 1 = unsuccessful termination (no restart done)

  • 2 = unsuccessful termination (restart done)

Note

The server returns the codes just described as of MySQL 5.7.6. Any management script written for older servers should be revised to handle three exit values if it checks only for 1 as a failure exit value.

6.2 The MySQL Data Directory

Information managed by the MySQL server is stored under a directory known as the data directory. The following list briefly describes the items typically found in the data directory, with cross references for additional information:

Some items in the preceding list can be relocated elsewhere by reconfiguring the server. In addition, the --datadir option enables the location of the data directory itself to be changed. For a given MySQL installation, check the server configuration to determine whether items have been moved.

6.3 The mysql System Database

The mysql database is the system database. It contains tables that store information required by the MySQL server as it runs.

Tables in the mysql database fall into these categories:

The remainder of this section enumerates the tables in each category, with cross references for additional information. System tables use the MyISAM storage engine unless otherwise indicated.

Grant System Tables

These system tables contain grant information about user accounts and the privileges held by them:

  • user: User accounts, global privileges, and other non-privilege columns.

  • db: Database-level privileges.

  • tables_priv: Table-level privileges.

  • columns_priv: Column-level privileges.

  • procs_priv: Stored procedure and function privileges.

  • proxies_priv: Proxy-user privileges.

For more information about the structure, contents, and purpose of the grant tables, see Section 7.2.2, “Grant Tables”.

Object Information System Tables

These system tables contain information about stored programs, user-defined functions, and server-side plugins:

Log System Tables

The server uses these system tables for logging:

  • general_log: The general query log table.

  • slow_log: The slow query log table.

Log tables use the CSV storage engine.

For more information, see Section 6.4, “MySQL Server Logs”.

Server-Side Help System Tables

These system tables contain server-side help information:

  • help_category: Information about help categories.

  • help_keyword: Keywords associated with help topics.

  • help_relation: Mappings between help keywords and topics.

  • help_topic: Help topic contents.

These tables use the InnoDB storage engine as of MySQL 5.7.5, MyISAM before that.

For more information, see Section 6.1.10, “Server-Side Help”.

Time Zone System Tables

These system tables contain time zone information:

  • time_zone: Time zone IDs and whether they use leap seconds.

  • time_zone_leap_second: When leap seconds occur.

  • time_zone_name: Mappings between time zone IDs and names.

  • time_zone_transition, time_zone_transition_type: Time zone descriptions.

These tables use the InnoDB storage engine as of MySQL 5.7.5, MyISAM before that.

For more information, see Section 11.6, “MySQL Server Time Zone Support”.

Replication System Tables

The server uses these system tables to support replication:

Optimizer System Tables

These system tables are for use by the optimizer:

These tables use the InnoDB storage engine.

Miscellaneous System Tables

Other system tables do not fall into the preceding categories:

6.4 MySQL Server Logs

MySQL Server has several logs that can help you find out what activity is taking place.

Log TypeInformation Written to Log
Error logProblems encountered starting, running, or stopping mysqld
General query logEstablished client connections and statements received from clients
Binary logStatements that change data (also used for replication)
Relay logData changes received from a replication master server
Slow query logQueries that took more than long_query_time seconds to execute
DDL log (metadata log)Metadata operations performed by DDL statements

By default, no logs are enabled, except the error log on Windows. (The DDL log is always created when required, and has no user-configurable options; see Section 6.4.6, “The DDL Log”.) The following log-specific sections provide information about the server options that enable logging.

By default, the server writes files for all enabled logs in the data directory. You can force the server to close and reopen the log files (or in some cases switch to a new log file) by flushing the logs. Log flushing occurs when you issue a FLUSH LOGS statement; execute mysqladmin with a flush-logs or refresh argument; or execute mysqldump with a --flush-logs or --master-data option. See Section 14.7.6.3, “FLUSH Syntax”, Section 5.5.2, “mysqladmin — Client for Administering a MySQL Server”, and Section 5.5.4, “mysqldump — A Database Backup Program”. In addition, the binary log is flushed when its size reaches the value of the max_binlog_size system variable.

You can control the general query and slow query logs during runtime. You can enable or disable logging, or change the log file name. You can tell the server to write general query and slow query entries to log tables, log files, or both. For details, see Section 6.4.1, “Selecting General Query and Slow Query Log Output Destinations”, Section 6.4.3, “The General Query Log”, and Section 6.4.5, “The Slow Query Log”.

The relay log is used only on slave replication servers, to hold data changes from the master server that must also be made on the slave. For discussion of relay log contents and configuration, see Section 18.2.4.1, “The Slave Relay Log”.

For information about log maintenance operations such as expiration of old log files, see Section 6.4.7, “Server Log Maintenance”.

For information about keeping logs secure, see Section 7.1.2.3, “Passwords and Logging”.

6.4.1 Selecting General Query and Slow Query Log Output Destinations

MySQL Server provides flexible control over the destination of output to the general query log and the slow query log, if those logs are enabled. Possible destinations for log entries are log files or the general_log and slow_log tables in the mysql database. Either or both destinations can be selected.

Log control at server startup. The --log-output option specifies the destination for log output. This option does not in itself enable the logs. Its syntax is --log-output[=value,...]:

  • If --log-output is given with a value, the value should be a comma-separated list of one or more of the words TABLE (log to tables), FILE (log to files), or NONE (do not log to tables or files). NONE, if present, takes precedence over any other specifiers.

  • If --log-output is omitted, the default logging destination is FILE.

The general_log system variable controls logging to the general query log for the selected log destinations. If specified at server startup, general_log takes an optional argument of 1 or 0 to enable or disable the log. To specify a file name other than the default for file logging, set the general_log_file variable. Similarly, the slow_query_log variable controls logging to the slow query log for the selected destinations and setting slow_query_log_file specifies a file name for file logging. If either log is enabled, the server opens the corresponding log file and writes startup messages to it. However, further logging of queries to the file does not occur unless the FILE log destination is selected.

Examples:

  • To write general query log entries to the log table and the log file, use --log-output=TABLE,FILE to select both log destinations and --general_log to enable the general query log.

  • To write general and slow query log entries only to the log tables, use --log-output=TABLE to select tables as the log destination and --general_log and --slow_query_log to enable both logs.

  • To write slow query log entries only to the log file, use --log-output=FILE to select files as the log destination and --slow_query_log to enable the slow query log. (In this case, because the default log destination is FILE, you could omit the --log-output option.)

Log control at runtime. The system variables associated with log tables and files enable runtime control over logging:

  • The global log_output system variable indicates the current logging destination. It can be modified at runtime to change the destination.

  • The global general_log and slow_query_log variables indicate whether the general query log and slow query log are enabled (ON) or disabled (OFF). You can set these variables at runtime to control whether the logs are enabled.

  • The global general_log_file and slow_query_log_file variables indicate the names of the general query log and slow query log files. You can set these variables at server startup or at runtime to change the names of the log files.

  • To disable or enable general query logging for the current connection, set the session sql_log_off variable to ON or OFF.

The use of tables for log output offers the following benefits:

  • Log entries have a standard format. To display the current structure of the log tables, use these statements:

    SHOW CREATE TABLE mysql.general_log;
    SHOW CREATE TABLE mysql.slow_log;
    
  • Log contents are accessible through SQL statements. This enables the use of queries that select only those log entries that satisfy specific criteria. For example, to select log contents associated with a particular client (which can be useful for identifying problematic queries from that client), it is easier to do this using a log table than a log file.

  • Logs are accessible remotely through any client that can connect to the server and issue queries (if the client has the appropriate log table privileges). It is not necessary to log in to the server host and directly access the file system.

The log table implementation has the following characteristics:

  • In general, the primary purpose of log tables is to provide an interface for users to observe the runtime execution of the server, not to interfere with its runtime execution.

  • CREATE TABLE, ALTER TABLE, and DROP TABLE are valid operations on a log table. For ALTER TABLE and DROP TABLE, the log table cannot be in use and must be disabled, as described later.

  • By default, the log tables use the CSV storage engine that writes data in comma-separated values format. For users who have access to the .CSV files that contain log table data, the files are easy to import into other programs such as spreadsheets that can process CSV input.

    The log tables can be altered to use the MyISAM storage engine. You cannot use ALTER TABLE to alter a log table that is in use. The log must be disabled first. No engines other than CSV or MyISAM are legal for the log tables.

  • To disable logging so that you can alter (or drop) a log table, you can use the following strategy. The example uses the general query log; the procedure for the slow query log is similar but uses the slow_log table and slow_query_log system variable.

    SET @old_log_state = @@global.general_log;
    SET GLOBAL general_log = 'OFF';
    ALTER TABLE mysql.general_log ENGINE = MyISAM;
    SET GLOBAL general_log = @old_log_state;
    
  • TRUNCATE TABLE is a valid operation on a log table. It can be used to expire log entries.

  • RENAME TABLE is a valid operation on a log table. You can atomically rename a log table (to perform log rotation, for example) using the following strategy:

    USE mysql;
    DROP TABLE IF EXISTS general_log2;
    CREATE TABLE general_log2 LIKE general_log;
    RENAME TABLE general_log TO general_log_backup, general_log2 TO general_log;
    
  • CHECK TABLE is a valid operation on a log table.

  • LOCK TABLES cannot be used on a log table.

  • INSERT, DELETE, and UPDATE cannot be used on a log table. These operations are permitted only internally to the server itself.

  • FLUSH TABLES WITH READ LOCK and the state of the read_only system variable have no effect on log tables. The server can always write to the log tables.

  • Entries written to the log tables are not written to the binary log and thus are not replicated to slave servers.

  • To flush the log tables or log files, use FLUSH TABLES or FLUSH LOGS, respectively.

  • Partitioning of log tables is not permitted.

  • A mysqldump dump includes statements to recreate those tables so that they are not missing after reloading the dump file. Log table contents are not dumped.

6.4.2 The Error Log

The error log contains information about mysqld startup and shutdown times, progress notes that occur during startup and shutdown, and critical errors that occur while the server is running. If mysqld notices a table that needs to be automatically checked or repaired, it writes a message to the error log.

On some operating systems, the error log contains a stack trace if mysqld exits abnormally. The trace can be used to determine where mysqld exited. See Section 28.5, “Debugging and Porting MySQL”.

Interpretation of error logging options differs somewhat for Windows and Unix systems, so be sure to use the information appropriate to your system.

mysqld_safe may write messages to the error log if it is used to start mysqld. For example, when mysqld_safe notices abnormal mysqld exits, it restarts mysqld and writes a mysqld restarted message to the error log.

In the following discussion, console means stderr, the standard error output. This is your terminal or console window unless the standard error output has been redirected.

Error Logging on Windows

On Windows, the --log-error, --pid-file, and --console options affect error logging:

  • Without --log-error, mysqld writes error messages to the default log file.

  • With --log-error[=file_name], mysqld writes error messages to an error log file. If no file is named, mysqld writes to the default log file. If a file is named, mysqld writes to it, creating it in the data directory unless an absolute path name is given to specify a different directory.

  • The default log file is host_name.err in the data directory, unless the --pid-file option is specified. In that case, the default name is the PID file base name with a suffix of .err in the data directory. This default is used if --log-error is not given, or is given without naming a log file.

  • With --console, mysqld writes error messages to the console. --log-error, if given, is ignored and has no effect. If both options are present, their order does not matter: --console takes precedence and error messages go to the console. (In MySQL 5.5 and 5.6, the precedence is reversed: --log-error causes --console to be ignored.)

In addition, on Windows, the server by default writes events and error messages to the Windows Event Log within the Application log.

  • Entries marked as Error, Warning, and Note are written to the Event Log, but not informational messages such as information statements from individual storage engines.

  • These log entries have a source of MySQL.

  • Information written to the Windows Event Log can be controlled using the log_syslog system variable, as described later.

If the server writes error messages to the console, it sets the log_error system variable to stderr. Otherwise, log_error indicates the error log file name. On Windows, --console overrides use of an error log file and sends error messages to the console, so the server sets log_error to stderr. This occurs even if --log-error is also given.

Error Logging on Unix and Unix-Like Systems

On Unix and Unix-like systems, mysqld writes error log messages as follows:

  • Without --log-error, mysqld writes error messages to the console.

  • With --log-error[=file_name], mysqld writes error messages to an error log file. If no file is named, mysqld writes to the default log file. If a file is named, mysqld writes to it, creating it in the data directory unless an absolute path name is given to specify a different directory.

  • The default log file is host_name.err in the data directory. This default is used if --log-error is given without naming a log file.

Note

It is common for Yum or APT package installations to configure an error log location under /var/log with an entry like log-error=/var/log/mysqld.log in a server configuration file. Removing the file name from the entry causes the default log file to be used, which is written to the data directory.

If the server writes error messages to the console, it sets the log_error system variable to stderr. Otherwise, log_error indicates the error log file name.

If you specify --log-error in an option file in a [mysqld], [server], or [mysqld_safe] section, mysqld_safe finds and uses the option.

Using Syslog for the Error Log

It is possible to have mysqld write the error log to syslog on Unix and Unix-like systems, and to the Windows Event Log on Windows. To do so, use these system variables:

  • log_syslog: Enable this variable to send the error log to syslog. In this case, the following system variables can also be used for finer control.

  • log_syslog_facility: The default facility for syslog messages is daemon. Set this variable to specify a different facility.

  • log_syslog_include_pid: Whether to include the server process ID in each line of syslog output.

  • log_syslog_tag: This variable defines a tag to add to the server identifier (mysqld) in syslog messages. If defined, the tag is appended to the identifier with a leading hyphen.

On Unix and Unix-like systems, control of output to syslog is also available using mysqld_safe, which can capture server error output and pass it to syslog.

Note

Using mysqld_safe for syslog error logging is deprecated; you should use the server system variables instead.

mysqld_safe has three error-logging options, --syslog, --skip-syslog, and --log-error. The default with no logging options or with --skip-syslog is to use the default log file. To explicitly specify use of an error log file, specify --log-error=file_name to mysqld_safe, and mysqld_safe will arrange for mysqld to write messages to a log file. To use syslog instead, specify the --syslog option. For syslog output, a tag can be specified with --syslog-tag=tag_val; this is appended to the mysqld server identifier with a leading hyphen.

Error Log Verbosity

The log_error_verbosity system variable controls server verbosity for writing error, warning, and note messages to the error log. Permitted values are 1 (errors only), 2 (errors and warnings), 3 (errors, warnings, and notes), with a default of 3. If the value is greater than 2, the server logs aborted connections and access-denied errors for new connection attempts. See Section B.5.2.11, “Communication Errors and Aborted Connections”.

Error Log Message Format

The log_timestamps system variable controls the timestamp time zone of messages written to the error log (as well as to general query log and slow query log files). Permitted values are UTC (the default) and SYSTEM (local system time zone).

The ID included in error log messages is that of the thread within mysqld responsible for writing the message. This indicates which part of the server produced the message, and is consistent with general query log and slow query log messages, which include the connection thread ID.

Flushing and Renaming the Error Log File

If you flush the logs using FLUSH LOGS or mysqladmin flush-logs and mysqld is writing the error log to a file (for example, if it was started with the --log-error option), the server closes and reopens the log file. To rename the file, do so manually before flushing. Flushing the logs then reopens a new file with the original file name. For example, to rename the file and create a new one, use the following commands (assuming a log file name of host_name.err):

shell> mv host_name.err host_name.err-old
shell> mysqladmin flush-logs
shell> mv host_name.err-old backup-directory

On Windows, use rename rather than mv.

If the location of the error file is not writable by the server, the log-flushing operation will fail to create a new log file. For example, on Linux, the server might write the error log as /var/log/mysqld.log, where /var/log is owned by root and not writable by mysqld. For information about handling this case, see Section 6.4.7, “Server Log Maintenance”.

If the server is not writing to a named file, no error log renaming occurs when the logs are flushed.

6.4.3 The General Query Log

The general query log is a general record of what mysqld is doing. The server writes information to this log when clients connect or disconnect, and it logs each SQL statement received from clients. The general query log can be very useful when you suspect an error in a client and want to know exactly what the client sent to mysqld.

Each line that shows when a client connects also includes using connection_type to indicate the protocol used to establish the connection. connection_type is one of TCP/IP (TCP/IP connection established without SSL), SSL/TLS (TCP/IP connection established with SSL), Socket (Unix socket file connection), Named Pipe (Windows named pipe connection), or Shared Memory (Windows shared memory connection).

mysqld writes statements to the query log in the order that it receives them, which might differ from the order in which they are executed. This logging order is in contrast with that of the binary log, for which statements are written after they are executed but before any locks are released. In addition, the query log may contain statements that only select data while such statements are never written to the binary log.

When using statement-based binary logging on a replication master server, statements received by its slaves are written to the query log of each slave. Statements are written to the query log of the master server if a client reads events with the mysqlbinlog utility and passes them to the server.

However, when using row-based binary logging, updates are sent as row changes rather than SQL statements, and thus these statements are never written to the query log when binlog_format is ROW. A given update also might not be written to the query log when this variable is set to MIXED, depending on the statement used. See Section 18.2.1.1, “Advantages and Disadvantages of Statement-Based and Row-Based Replication”, for more information.

By default, the general query log is disabled. To specify the initial general query log state explicitly, use --general_log[={0|1}]. With no argument or an argument of 1, --general_log enables the log. With an argument of 0, this option disables the log. To specify a log file name, use --general_log_file=file_name. To specify the log destination, use --log-output (as described in Section 6.4.1, “Selecting General Query and Slow Query Log Output Destinations”).

If you specify no name for the general query log file, the default name is host_name.log. The server creates the file in the data directory unless an absolute path name is given to specify a different directory.

To disable or enable the general query log or change the log file name at runtime, use the global general_log and general_log_file system variables. Set general_log to 0 (or OFF) to disable the log or to 1 (or ON) to enable it. Set general_log_file to specify the name of the log file. If a log file already is open, it is closed and the new file is opened.

When the general query log is enabled, the server writes output to any destinations specified by the --log-output option or log_output system variable. If you enable the log, the server opens the log file and writes startup messages to it. However, further logging of queries to the file does not occur unless the FILE log destination is selected. If the destination is NONE, the server writes no queries even if the general log is enabled. Setting the log file name has no effect on logging if the log destination value does not contain FILE.

Server restarts and log flushing do not cause a new general query log file to be generated (although flushing closes and reopens it). To rename the file and create a new one, use the following commands:

shell> mv host_name.log host_name-old.log
shell> mysqladmin flush-logs
shell> mv host_name-old.log backup-directory

On Windows, use rename rather than mv.

You can also rename the general query log file at runtime by disabling the log:

SET GLOBAL general_log = 'OFF';

With the log disabled, rename the log file externally; for example, from the command line. Then enable the log again:

SET GLOBAL general_log = 'ON';

This method works on any platform and does not require a server restart.

The session sql_log_off variable can be set to ON or OFF to disable or enable general query logging for the current connection.

Passwords in statements written to the general query log are rewritten by the server not to occur literally in plain text. Password rewriting can be suppressed for the general query log by starting the server with the --log-raw option. This option may be useful for diagnostic purposes, to see the exact text of statements as received by the server, but for security reasons is not recommended for production use. See also Section 7.1.2.3, “Passwords and Logging”.

An implication of password rewriting is that statements that cannot be parsed (due, for example, to syntax errors) are not written to the general query log because they cannot be known to be password free. Use cases that require logging of all statements including those with errors should use the --log-raw option, bearing in mind that this also bypasses password rewriting.

Password rewriting occurs only when plain text passwords are expected. For statements with syntax that expect a password hash value, no rewriting occurs. If a plain text password is supplied erroneously for such syntax, the password is logged as given, without rewriting. For example, the following statement is logged as shown because a password hash value is expected:

CREATE USER 'user1'@'localhost' IDENTIFIED BY PASSWORD 'not-so-secret';

The log_timestamps system variable controls the timestamp time zone of messages written to the general query log file (as well as to the slow query log file and the error log). It does not affect the time zone of general query log and slow query log messages written to log tables, but rows retrieved from those tables can be converted from the local system time zone to any desired time zone with CONVERT_TZ() or by setting the session time_zone system variable.

6.4.4 The Binary Log

The binary log contains events that describe database changes such as table creation operations or changes to table data. It also contains events for statements that potentially could have made changes (for example, a DELETE which matched no rows), unless row-based logging is used. The binary log also contains information about how long each statement took that updated data. The binary log has two important purposes:

  • For replication, the binary log on a master replication server provides a record of the data changes to be sent to slave servers. The master server sends the events contained in its binary log to its slaves, which execute those events to make the same data changes that were made on the master. See Section 18.2, “Replication Implementation”.

  • Certain data recovery operations require use of the binary log. After a backup has been restored, the events in the binary log that were recorded after the backup was made are re-executed. These events bring databases up to date from the point of the backup. See Section 8.5, “Point-in-Time (Incremental) Recovery Using the Binary Log”.

The binary log is not used for statements such as SELECT or SHOW that do not modify data. To log all statements (for example, to identify a problem query), use the general query log. See Section 6.4.3, “The General Query Log”.

Running a server with binary logging enabled makes performance slightly slower. However, the benefits of the binary log in enabling you to set up replication and for restore operations generally outweigh this minor performance decrement.

The binary log is generally resilient to unexpected halts because only complete transactions are logged or read back. See Section 18.3.2, “Handling an Unexpected Halt of a Replication Slave” for more information.

Passwords in statements written to the binary log are rewritten by the server not to occur literally in plain text. See also Section 7.1.2.3, “Passwords and Logging”.

The following discussion describes some of the server options and variables that affect the operation of binary logging. For a complete list, see Section 18.1.6.4, “Binary Logging Options and Variables”.

To enable the binary log, start the server with the --log-bin[=base_name] option. If no base_name value is given, the default name is the value of the pid-file option (which by default is the name of host machine) followed by -bin. If the base name is given, the server writes the file in the data directory unless the base name is given with a leading absolute path name to specify a different directory. It is recommended that you specify a base name explicitly rather than using the default of the host name; see Section B.5.7, “Known Issues in MySQL”, for the reason.

If you supply an extension in the log name (for example, --log-bin=base_name.extension), the extension is silently removed and ignored.

mysqld appends a numeric extension to the binary log base name to generate binary log file names. The number increases each time the server creates a new log file, thus creating an ordered series of files. The server creates a new file in the series each time it starts or flushes the logs. The server also creates a new binary log file automatically after the current log's size reaches max_binlog_size. A binary log file may become larger than max_binlog_size if you are using large transactions because a transaction is written to the file in one piece, never split between files.

To keep track of which binary log files have been used, mysqld also creates a binary log index file that contains the names of all used binary log files. By default, this has the same base name as the binary log file, with the extension '.index'. You can change the name of the binary log index file with the --log-bin-index[=file_name] option. You should not manually edit this file while mysqld is running; doing so would confuse mysqld.

The term binary log file generally denotes an individual numbered file containing database events. The term binary log collectively denotes the set of numbered binary log files plus the index file.

A client that has the SUPER privilege can disable binary logging of its own statements by using a SET sql_log_bin=0 statement. See Section 6.1.5, “Server System Variables”.

By default, the server logs the length of the event as well as the event itself and uses this to verify that the event was written correctly. You can also cause the server to write checksums for the events by setting the binlog_checksum system variable. When reading back from the binary log, the master uses the event length by default, but can be made to use checksums if available by enabling the master_verify_checksum system variable. The slave I/O thread also verifies events received from the master. You can cause the slave SQL thread to use checksums if available when reading from the relay log by enabling the slave_sql_verify_checksum system variable.

The format of the events recorded in the binary log is dependent on the binary logging format. Three format types are supported, row-based logging, statement-based logging and mixed-base logging. The binary logging format used depends on the MySQL version. For general descriptions of the logging formats, see Section 6.4.4.1, “Binary Logging Formats”. For detailed information about the format of the binary log, see MySQL Internals: The Binary Log.

The server evaluates the --binlog-do-db and --binlog-ignore-db options in the same way as it does the --replicate-do-db and --replicate-ignore-db options. For information about how this is done, see Section 18.2.5.1, “Evaluation of Database-Level Replication and Binary Logging Options”.

A replication slave server by default does not write to its own binary log any data modifications that are received from the replication master. To log these modifications, start the slave with the --log-slave-updates option in addition to the --log-bin option (see Section 18.1.6.3, “Replication Slave Options and Variables”). This is done when a slave is also to act as a master to other slaves in chained replication.

You can delete all binary log files with the RESET MASTER statement, or a subset of them with PURGE BINARY LOGS. See Section 14.7.6.6, “RESET Syntax”, and Section 14.4.1.1, “PURGE BINARY LOGS Syntax”.

If you are using replication, you should not delete old binary log files on the master until you are sure that no slave still needs to use them. For example, if your slaves never run more than three days behind, once a day you can execute mysqladmin flush-logs on the master and then remove any logs that are more than three days old. You can remove the files manually, but it is preferable to use PURGE BINARY LOGS, which also safely updates the binary log index file for you (and which can take a date argument). See Section 14.4.1.1, “PURGE BINARY LOGS Syntax”.

You can display the contents of binary log files with the mysqlbinlog utility. This can be useful when you want to reprocess statements in the log for a recovery operation. For example, you can update a MySQL server from the binary log as follows:

shell> mysqlbinlog log_file | mysql -h server_name

mysqlbinlog also can be used to display replication slave relay log file contents because they are written using the same format as binary log files. For more information on the mysqlbinlog utility and how to use it, see Section 5.6.7, “mysqlbinlog — Utility for Processing Binary Log Files”. For more information about the binary log and recovery operations, see Section 8.5, “Point-in-Time (Incremental) Recovery Using the Binary Log”.

Binary logging is done immediately after a statement or transaction completes but before any locks are released or any commit is done. This ensures that the log is logged in commit order.

Updates to nontransactional tables are stored in the binary log immediately after execution.

Within an uncommitted transaction, all updates (UPDATE, DELETE, or INSERT) that change transactional tables such as InnoDB tables are cached until a COMMIT statement is received by the server. At that point, mysqld writes the entire transaction to the binary log before the COMMIT is executed.

Modifications to nontransactional tables cannot be rolled back. If a transaction that is rolled back includes modifications to nontransactional tables, the entire transaction is logged with a ROLLBACK statement at the end to ensure that the modifications to those tables are replicated.

When a thread that handles the transaction starts, it allocates a buffer of binlog_cache_size to buffer statements. If a statement is bigger than this, the thread opens a temporary file to store the transaction. The temporary file is deleted when the thread ends.

The Binlog_cache_use status variable shows the number of transactions that used this buffer (and possibly a temporary file) for storing statements. The Binlog_cache_disk_use status variable shows how many of those transactions actually had to use a temporary file. These two variables can be used for tuning binlog_cache_size to a large enough value that avoids the use of temporary files.

The max_binlog_cache_size system variable (default 4GB, which is also the maximum) can be used to restrict the total size used to cache a multiple-statement transaction. If a transaction is larger than this many bytes, it fails and rolls back. The minimum value is 4096.

If you are using the binary log and row based logging, concurrent inserts are converted to normal inserts for CREATE ... SELECT or INSERT ... SELECT statements. This is done to ensure that you can re-create an exact copy of your tables by applying the log during a backup operation. If you are using statement-based logging, the original statement is written to the log.

The binary log format has some known limitations that can affect recovery from backups. See Section 18.4.1, “Replication Features and Issues”.

Binary logging for stored programs is done as described in Section 23.7, “Binary Logging of Stored Programs”.

Note that the binary log format differs in MySQL 5.7 from previous versions of MySQL, due to enhancements in replication. See Section 18.4.2, “Replication Compatibility Between MySQL Versions”.

Writes to the binary log file and binary log index file are handled in the same way as writes to MyISAM tables. See Section B.5.3.4, “How MySQL Handles a Full Disk”.

As of MySQL 5.7.7, the binary log is synchronized to disk at each write by default (sync_binlog=1). Prior to MySQL 5.7.7, it is not (sync_binlog=0). So, prior to MySQL 5.7.7, if the operating system or machine (not only the MySQL server) crashes, there is a chance that the last statements of the binary log are lost. To prevent this, use the sync_binlog system variable to synchronize the binary log to disk after every N commit groups. See Section 6.1.5, “Server System Variables”. The safest value for sync_binlog is 1, but this is also the slowest. Even with sync_binlog set to 1, there is still the chance of inconsistency between the table content and binary log content in case of a crash.

For example, if you are using InnoDB tables and the MySQL server processes a COMMIT statement, it writes many prepared transactions to the binary log in sequence, synchronizes the binary log, and then commits this transaction into InnoDB. If the server crashes between those two operations, the transaction is rolled back by InnoDB at restart but still exists in the binary log. Such an issue is resolved assuming --innodb_support_xa is set to 1, the default. Although this option is related to the support of XA transactions in InnoDB, it also ensures that the binary log and InnoDB data files are synchronized. For this option to provide a greater degree of safety, the MySQL server should also be configured to synchronize the binary log and the InnoDB logs to disk before committing the transaction. The InnoDB logs are synchronized by default, and sync_binlog=1 can be used to synchronize the binary log. The effect of this option is that at restart after a crash, after doing a rollback of transactions, the MySQL server scans the latest binary log file to collect transaction xid values and calculate the last valid position in the binary log file. The MySQL server then tells InnoDB to complete any prepared transactions that were successfully written to the to the binary log, and truncates the binary log to the last valid position. This ensures that the binary log reflects the exact data of InnoDB tables, and therefore the slave remains in synchrony with the master because it does not receive a statement which has been rolled back.

Note

innodb_support_xa is deprecated and will be removed in a future release. InnoDB support for two-phase commit in XA transactions is always enabled as of MySQL 5.7.10.

If the MySQL server discovers at crash recovery that the binary log is shorter than it should have been, it lacks at least one successfully committed InnoDB transaction. This should not happen if sync_binlog=1 and the disk/file system do an actual sync when they are requested to (some do not), so the server prints an error message The binary log file_name is shorter than its expected size. In this case, this binary log is not correct and replication should be restarted from a fresh snapshot of the master's data.

The session values of the following system variables are written to the binary log and honored by the replication slave when parsing the binary log:

6.4.4.1 Binary Logging Formats

The server uses several logging formats to record information in the binary log. The exact format employed depends on the version of MySQL being used. There are three logging formats:

  • Replication capabilities in MySQL originally were based on propagation of SQL statements from master to slave. This is called statement-based logging. You can cause this format to be used by starting the server with --binlog-format=STATEMENT.

  • In row-based logging, the master writes events to the binary log that indicate how individual table rows are affected. It is important therefore that tables always use a primary key to ensure rows can be efficiently identified. You can cause the server to use row-based logging by starting it with --binlog-format=ROW.

  • A third option is also available: mixed logging. With mixed logging, statement-based logging is used by default, but the logging mode switches automatically to row-based in certain cases as described below. You can cause MySQL to use mixed logging explicitly by starting mysqld with the option --binlog-format=MIXED.

Prior to MySQL 5.7.7, statement-based logging format was the default. In MySQL 5.7.7 and later, row-based logging format is the default.

The logging format can also be set or limited by the storage engine being used. This helps to eliminate issues when replicating certain statements between a master and slave which are using different storage engines.

With statement-based replication, there may be issues with replicating nondeterministic statements. In deciding whether or not a given statement is safe for statement-based replication, MySQL determines whether it can guarantee that the statement can be replicated using statement-based logging. If MySQL cannot make this guarantee, it marks the statement as potentially unreliable and issues the warning, Statement may not be safe to log in statement format.

You can avoid these issues by using MySQL's row-based replication instead.

6.4.4.2 Setting The Binary Log Format

You can select the binary logging format explicitly by starting the MySQL server with --binlog-format=type. The supported values for type are:

  • STATEMENT causes logging to be statement based.

  • ROW causes logging to be row based.

  • MIXED causes logging to use mixed format.

Prior to MySQL 5.7.7, statement-based logging format was the default. In MySQL 5.7.7 and later, row-based logging format is the default.

The logging format also can be switched at runtime. To specify the format globally for all clients, set the global value of the binlog_format system variable:

mysql> SET GLOBAL binlog_format = 'STATEMENT';
mysql> SET GLOBAL binlog_format = 'ROW';
mysql> SET GLOBAL binlog_format = 'MIXED';

An individual client can control the logging format for its own statements by setting the session value of binlog_format:

mysql> SET SESSION binlog_format = 'STATEMENT';
mysql> SET SESSION binlog_format = 'ROW';
mysql> SET SESSION binlog_format = 'MIXED';
Note

Each MySQL Server can set its own and only its own binary logging format (true whether binlog_format is set with global or session scope). This means that changing the logging format on a replication master does not cause a slave to change its logging format to match. (When using STATEMENT mode, the binlog_format system variable is not replicated; when using MIXED or ROW logging mode, it is replicated but is ignored by the slave.) Changing the binary logging format on the master while replication is ongoing, or without also changing it on the slave can cause replication to fail with errors such as Error executing row event: 'Cannot execute statement: impossible to write to binary log since statement is in row format and BINLOG_FORMAT = STATEMENT.'

To change the global or session binlog_format value, you must have the SUPER privilege.

There are several reasons why a client might want to set binary logging on a per-session basis:

  • A session that makes many small changes to the database might want to use row-based logging.

  • A session that performs updates that match many rows in the WHERE clause might want to use statement-based logging because it will be more efficient to log a few statements than many rows.

  • Some statements require a lot of execution time on the master, but result in just a few rows being modified. It might therefore be beneficial to replicate them using row-based logging.

There are exceptions when you cannot switch the replication format at runtime:

  • From within a stored function or a trigger

  • If the NDB storage engine is enabled

  • If the session is currently in row-based replication mode and has open temporary tables

Trying to switch the format in any of these cases results in an error.

If you are using InnoDB tables and the transaction isolation level is READ COMMITTED or READ UNCOMMITTED, only row-based logging can be used. It is possible to change the logging format to STATEMENT, but doing so at runtime leads very rapidly to errors because InnoDB can no longer perform inserts.

Switching the replication format at runtime is not recommended when any temporary tables exist, because temporary tables are logged only when using statement-based replication, whereas with row-based replication they are not logged. With mixed replication, temporary tables are usually logged; exceptions happen with user-defined functions (UDFs) and with the UUID() function.

With the binary log format set to ROW, many changes are written to the binary log using the row-based format. Some changes, however, still use the statement-based format. Examples include all DDL (data definition language) statements such as CREATE TABLE, ALTER TABLE, or DROP TABLE.

The --binlog-row-event-max-size option is available for servers that are capable of row-based replication. Rows are stored into the binary log in chunks having a size in bytes not exceeding the value of this option. The value must be a multiple of 256. The default value is 8192.

Warning

When using statement-based logging for replication, it is possible for the data on the master and slave to become different if a statement is designed in such a way that the data modification is nondeterministic; that is, it is left to the will of the query optimizer. In general, this is not a good practice even outside of replication. For a detailed explanation of this issue, see Section B.5.7, “Known Issues in MySQL”.

For information about logs kept by replication slaves, see Section 18.2.4, “Replication Relay and Status Logs”.

6.4.4.3 Mixed Binary Logging Format

When running in MIXED logging format, the server automatically switches from statement-based to row-based logging under the following conditions:

Note

A warning is generated if you try to execute a statement using statement-based logging that should be written using row-based logging. The warning is shown both in the client (in the output of SHOW WARNINGS) and through the mysqld error log. A warning is added to the SHOW WARNINGS table each time such a statement is executed. However, only the first statement that generated the warning for each client session is written to the error log to prevent flooding the log.

In addition to the decisions above, individual engines can also determine the logging format used when information in a table is updated. The logging capabilities of an individual engine can be defined as follows:

  • If an engine supports row-based logging, the engine is said to be row-logging capable.

  • If an engine supports statement-based logging, the engine is said to be statement-logging capable.

A given storage engine can support either or both logging formats. The following table lists the formats supported by each engine.

Storage EngineRow Logging SupportedStatement Logging Supported
ARCHIVEYesYes
BLACKHOLEYesYes
CSVYesYes
EXAMPLEYesNo
FEDERATEDYesYes
HEAPYesYes
InnoDBYesYes when the transaction isolation level is REPEATABLE READ or SERIALIZABLE; No otherwise.
MyISAMYesYes
MERGEYesYes
NDBYesNo

Whether a statement is to be logged and the logging mode to be used is determined according to the type of statement (safe, unsafe, or binary injected), the binary logging format (STATEMENT, ROW, or MIXED), and the logging capabilities of the storage engine (statement capable, row capable, both, or neither). (Binary injection refers to logging a change that must be logged using ROW format.)

Statements may be logged with or without a warning; failed statements are not logged, but generate errors in the log. This is shown in the following decision table, where SLC stands for statement-logging capable and RLC stands for row-logging capable.

ConditionAction
Typebinlog_formatSLCRLCError / WarningLogged as
**NoNoError: Cannot execute statement: Binary logging is impossible since at least one engine is involved that is both row-incapable and statement-incapable.-
SafeSTATEMENTYesNo-STATEMENT
SafeMIXEDYesNo-STATEMENT
SafeROWYesNoError: Cannot execute statement: Binary logging is impossible since BINLOG_FORMAT = ROW and at least one table uses a storage engine that is not capable of row-based logging.-
UnsafeSTATEMENTYesNoWarning: Unsafe statement binlogged in statement format, since BINLOG_FORMAT = STATEMENTSTATEMENT
UnsafeMIXEDYesNoError: Cannot execute statement: Binary logging of an unsafe statement is impossible when the storage engine is limited to statement-based logging, even if BINLOG_FORMAT = MIXED.-
UnsafeROWYesNoError: Cannot execute statement: Binary logging is impossible since BINLOG_FORMAT = ROW and at least one table uses a storage engine that is not capable of row-based logging.-
Row InjectionSTATEMENTYesNoError: Cannot execute row injection: Binary logging is not possible since at least one table uses a storage engine that is not capable of row-based logging.-
Row InjectionMIXEDYesNoError: Cannot execute row injection: Binary logging is not possible since at least one table uses a storage engine that is not capable of row-based logging.-
Row InjectionROWYesNoError: Cannot execute row injection: Binary logging is not possible since at least one table uses a storage engine that is not capable of row-based logging.-
SafeSTATEMENTNoYesError: Cannot execute statement: Binary logging is impossible since BINLOG_FORMAT = STATEMENT and at least one table uses a storage engine that is not capable of statement-based logging.-
SafeMIXEDNoYes-ROW
SafeROWNoYes-ROW
UnsafeSTATEMENTNoYesError: Cannot execute statement: Binary logging is impossible since BINLOG_FORMAT = STATEMENT and at least one table uses a storage engine that is not capable of statement-based logging.-
UnsafeMIXEDNoYes-ROW
UnsafeROWNoYes-ROW
Row InjectionSTATEMENTNoYesError: Cannot execute row injection: Binary logging is not possible since BINLOG_FORMAT = STATEMENT.-
Row InjectionMIXEDNoYes-ROW
Row InjectionROWNoYes-ROW
SafeSTATEMENTYesYes-STATEMENT
SafeMIXEDYesYes-STATEMENT
SafeROWYesYes-ROW
UnsafeSTATEMENTYesYesWarning: Unsafe statement binlogged in statement format since BINLOG_FORMAT = STATEMENT.STATEMENT
UnsafeMIXEDYesYes-ROW
UnsafeROWYesYes-ROW
Row InjectionSTATEMENTYesYesError: Cannot execute row injection: Binary logging is not possible because BINLOG_FORMAT = STATEMENT.-
Row InjectionMIXEDYesYes-ROW
Row InjectionROWYesYes-ROW

When a warning is produced by the determination, a standard MySQL warning is produced (and is available using SHOW WARNINGS). The information is also written to the mysqld error log. Only one error for each error instance per client connection is logged to prevent flooding the log. The log message includes the SQL statement that was attempted.

If a slave server was started with log_error_verbosity set to display warnings, the slave prints messages to the error log to provide information about its status, such as the binary log and relay log coordinates where it starts its job, when it is switching to another relay log, when it reconnects after a disconnect, statements that are unsafe for statement-based logging, and so forth.

6.4.4.4 Logging Format for Changes to mysql Database Tables

The contents of the grant tables in the mysql database can be modified directly (for example, with INSERT or DELETE) or indirectly (for example, with GRANT or CREATE USER). Statements that affect mysql database tables are written to the binary log using the following rules:

CREATE TABLE ... SELECT is a combination of data definition and data manipulation. The CREATE TABLE part is logged using statement format and the SELECT part is logged according to the value of binlog_format.

6.4.5 The Slow Query Log

The slow query log consists of SQL statements that took more than long_query_time seconds to execute and required at least min_examined_row_limit rows to be examined. The minimum and default values of long_query_time are 0 and 10, respectively. The value can be specified to a resolution of microseconds. For logging to a file, times are written including the microseconds part. For logging to tables, only integer times are written; the microseconds part is ignored.

By default, administrative statements are not logged, nor are queries that do not use indexes for lookups. This behavior can be changed using log_slow_admin_statements and log_queries_not_using_indexes, as described later.

The time to acquire the initial locks is not counted as execution time. mysqld writes a statement to the slow query log after it has been executed and after all locks have been released, so log order might differ from execution order.

By default, the slow query log is disabled. To specify the initial slow query log state explicitly, use --slow_query_log[={0|1}]. With no argument or an argument of 1, --slow_query_log enables the log. With an argument of 0, this option disables the log. To specify a log file name, use --slow_query_log_file=file_name. To specify the log destination, use --log-output (as described in Section 6.4.1, “Selecting General Query and Slow Query Log Output Destinations”).

If you specify no name for the slow query log file, the default name is host_name-slow.log. The server creates the file in the data directory unless an absolute path name is given to specify a different directory.

To disable or enable the slow query log or change the log file name at runtime, use the global slow_query_log and slow_query_log_file system variables. Set slow_query_log to 0 (or OFF) to disable the log or to 1 (or ON) to enable it. Set slow_query_log_file to specify the name of the log file. If a log file already is open, it is closed and the new file is opened.

When the slow query log is enabled, the server writes output to any destinations specified by the --log-output option or log_output system variable. If you enable the log, the server opens the log file and writes startup messages to it. However, further logging of queries to the file does not occur unless the FILE log destination is selected. If the destination is NONE, the server writes no queries even if the slow query log is enabled. Setting the log file name has no effect on logging if the log destination value does not contain FILE.

The server writes less information to the slow query log if you use the --log-short-format option.

To include slow administrative statements in the statements written to the slow query log, use the log_slow_admin_statements system variable. Administrative statements include ALTER TABLE, ANALYZE TABLE, CHECK TABLE, CREATE INDEX, DROP INDEX, OPTIMIZE TABLE, and REPAIR TABLE.

To include queries that do not use indexes for row lookups in the statements written to the slow query log, enable the log_queries_not_using_indexes system variable. When such queries are logged, the slow query log may grow quickly. It is possible to put a rate limit on these queries by setting the log_throttle_queries_not_using_indexes system variable. By default, this variable is 0, which means there is no limit. Positive values impose a per-minute limit on logging of queries that do not use indexes. The first such query opens a 60-second window within which the server logs queries up to the given limit, then suppresses additional queries. If there are suppressed queries when the window ends, the server logs a summary that indicates how many there were and the aggregate time spent in them. The next 60-second window begins when the server logs the next query that does not use indexes.

The server uses the controlling parameters in the following order to determine whether to write a query to the slow query log:

  1. The query must either not be an administrative statement, or log_slow_admin_statements must be enabled.

  2. The query must have taken at least long_query_time seconds, or log_queries_not_using_indexes must be enabled and the query used no indexes for row lookups.

  3. The query must have examined at least min_examined_row_limit rows.

  4. The query must not be suppressed according to the log_throttle_queries_not_using_indexes setting.

The log_timestamps system variable controls the timestamp time zone of messages written to the slow query log file (as well as to the general query log file and the error log). It does not affect the time zone of general query log and slow query log messages written to log tables, but rows retrieved from those tables can be converted from the local system time zone to any desired time zone with CONVERT_TZ() or by setting the session time_zone system variable.

All log lines contain a timestamp.

The server does not write queries handled by the query cache to the slow query log, nor queries that would not benefit from the presence of an index because the table has zero rows or one row.

By default, a replication slave does not write replicated queries to the slow query log. To change this, use the log_slow_slave_statements system variable.

Passwords in statements written to the slow query log are rewritten by the server not to occur literally in plain text. See also Section 7.1.2.3, “Passwords and Logging”.

The slow query log can be used to find queries that take a long time to execute and are therefore candidates for optimization. However, examining a long slow query log can become a difficult task. To make this easier, you can process a slow query log file using the mysqldumpslow command to summarize the queries that appear in the log. See Section 5.6.8, “mysqldumpslow — Summarize Slow Query Log Files”.

6.4.6 The DDL Log

The DDL log, or metadata log, records metadata operations generated by data definition statements such as DROP TABLE and ALTER TABLE. MySQL uses this log to recover from crashes occurring in the middle of a metadata operation. When executing the statement DROP TABLE t1, t2, we need to ensure that both t1 and t2 are dropped, and that each table drop is complete. Another example of this type of SQL statement is ALTER TABLE t3 DROP PARTITION p2, where we must make certain that the partition is completely dropped and that its definition is removed from the list of partitions for table t3.

A record of metadata operations such as those just described are written to the file ddl_log.log, in the MySQL data directory. This is a binary file; it is not intended to be human-readable, and you should not attempt to modify its contents in any way.

ddl_log.log is not created until it is actually needed for recording metadata statements, and is removed following a successful start of mysqld. Thus, it is possible for this file not to be present on a MySQL server that is functioning in a completely normal manner.

Currently, ddl_log.log can hold up to 1048573 entries, equivalent 4 GB in size. Once this limit is exceeded, you must rename or remove the file before it is possible to execute any additional DDL statements. This is a known issue which we are working to resolve (Bug #83708).

There are no user-configurable server options or variables associated with this file.

6.4.7 Server Log Maintenance

As described in Section 6.4, “MySQL Server Logs”, MySQL Server can create several different log files to help you see what activity is taking place. However, you must clean up these files regularly to ensure that the logs do not take up too much disk space.

When using MySQL with logging enabled, you may want to back up and remove old log files from time to time and tell MySQL to start logging to new files. See Section 8.2, “Database Backup Methods”.

On a Linux (Red Hat) installation, you can use the mysql-log-rotate script for this. If you installed MySQL from an RPM distribution, this script should have been installed automatically. Be careful with this script if you are using the binary log for replication. You should not remove binary logs until you are certain that their contents have been processed by all slaves.

On other systems, you must install a short script yourself that you start from cron (or its equivalent) for handling log files.

For the binary log, you can set the expire_logs_days system variable to expire binary log files automatically after a given number of days (see Section 6.1.5, “Server System Variables”). If you are using replication, you should set the variable no lower than the maximum number of days your slaves might lag behind the master. To remove binary logs on demand, use the PURGE BINARY LOGS statement (see Section 14.4.1.1, “PURGE BINARY LOGS Syntax”).

You can force MySQL to start using new log files by flushing the logs. Log flushing occurs when you issue a FLUSH LOGS statement or execute a mysqladmin flush-logs, mysqladmin refresh, mysqldump --flush-logs, or mysqldump --master-data command. See Section 14.7.6.3, “FLUSH Syntax”, Section 5.5.2, “mysqladmin — Client for Administering a MySQL Server”, and Section 5.5.4, “mysqldump — A Database Backup Program”. In addition, the binary log is flushed when its size reaches the value of the max_binlog_size system variable.

FLUSH LOGS supports optional modifiers to enable selective flushing of individual logs (for example, FLUSH BINARY LOGS).

A log-flushing operation does the following:

  • If general query logging or slow query logging to a log file is enabled, the server closes and reopens the general query log file or slow query log file.

  • If binary logging is enabled, the server closes the current binary log file and opens a new log file with the next sequence number.

  • If the server was started with the --log-error option to cause the error log to be written to a file, the server closes and reopens the log file.

The server creates a new binary log file when you flush the logs. However, it just closes and reopens the general and slow query log files. To cause new files to be created on Unix, rename the current log files before flushing them. At flush time, the server opens new log files with the original names. For example, if the general and slow query log files are named mysql.log and mysql-slow.log, you can use a series of commands like this:

shell> cd mysql-data-directory
shell> mv mysql.log mysql.old
shell> mv mysql-slow.log mysql-slow.old
shell> mysqladmin flush-logs

On Windows, use rename rather than mv.

At this point, you can make a backup of mysql.old and mysql-slow.old and then remove them from disk.

A similar strategy can be used to back up the error log file, if there is one.

You can rename the general query log or slow query log at runtime by disabling the log:

SET GLOBAL general_log = 'OFF';
SET GLOBAL slow_query_log = 'OFF';

With the logs disabled, rename the log files externally; for example, from the command line. Then enable the logs again:

SET GLOBAL general_log = 'ON';
SET GLOBAL slow_query_log = 'ON';

This method works on any platform and does not require a server restart.

Note

For the server to recreate a given log file after you have renamed the file externally, the file location must be writable by the server. This may not always be the case. For example, on Linux, the server might write the error log as /var/log/mysqld.log, where /var/log is owned by root and not writable by mysqld. In this case, the log-flushing operation will fail to create a new log file.

To handle this situation, you must manually create the new log file with the proper ownershiop after renaming the original log file. For example, execute these commands as root:

shell> mv /var/log/mysqld.log /var/log/mysqld.log.old
shell> install -omysql -gmysql -m0644 /dev/null /var/log/mysqld.log

6.5 MySQL Server Plugins

MySQL supports a plugin API that enables creation of server components. Plugins can be loaded at server startup, or loaded and unloaded at runtime without restarting the server. The components supported by this interface include, but are not limited to, storage engines, INFORMATION_SCHEMA tables, full-text parser plugins, partitioning support, and server extensions.

6.5.1 Server Plugins Available

MySQL distributions include several plugins that implement server extensions:

The following sections describe how to install and uninstall plugins, and how to determine at runtime which plugins are installed and obtain information about them. For information about writing plugins, see Section 28.2, “The MySQL Plugin API”.

6.5.2 Installing and Uninstalling Plugins

Server plugins must be loaded into the server before they can be used. MySQL supports plugin loading at server startup and runtime. It is also possible to control the activation state of loaded plugins at startup, and to unload them at runtime.

While a plugin is loaded, information about it is available at runtime from the INFORMATION_SCHEMA.PLUGINS table and the SHOW PLUGINS statement. See Section 6.5.3, “Obtaining Server Plugin Information”.

Installing Plugins

Before a server plugin can be used, it must be installed using one of the following methods. In the descriptions, plugin_name stands for a plugin name such as innodb, csv, or validate_password.

Built-in plugins:

A built-in plugin is known by the server automatically. Normally, the server enables the plugin at startup. Some built-in plugins permit this to be changed with the --plugin_name[=activation_state] option.

Plugins registered in the mysql.plugin system table:

The mysql.plugin table serves as a registry of plugins (other than built-in plugins, which need not be registered). At startup, the server loads each plugin listed in the table. Normally, for a plugin loaded from the mysql.plugin table, the server also enables the plugin. This can be changed with the --plugin_name[=activation_state] option.

If the server is started with the --skip-grant-tables option, it does not consult the mysql.plugin table and does not load the plugins listed there.

Plugins named with command-line options:

A plugin located in a plugin library file can be loaded at server startup with the --plugin-load, --plugin-load-add, or (as of MySQL 5.7.11) --early-plugin-load option. Normally, for a plugin loaded at startup, the server also enables the plugin. This can be changed with the --plugin_name[=activation_state] option.

The --plugin-load and --plugin-load-add options load plugins after built-in plugins and storage engines have initialized during the server startup sequence. The --early-plugin-load option is used to load plugins that must be available prior to initialization of built-in plugins and storage engines.

The value of each plugin-loading option is a semicolon-separated list of name=plugin_library and plugin_library values. Each name is the name of a plugin to load, and plugin_library is the name of the library file that contains the plugin code. If a plugin library is named without any preceding plugin name, the server loads all plugins in the library. The server looks for plugin library files in the directory named by the plugin_dir system variable.

Plugin-loading options do not register any plugin in the mysql.plugin table. For subsequent restarts, the server loads the plugin again only if --plugin-load, --plugin-load-add, or --early-plugin-load is given again. That is, the option produces a one-time plugin-installation operation that persists for a single server invocation.

--plugin-load, --plugin-load-add, and --early-plugin-load enable plugins to be loaded even when --skip-grant-tables is given (which causes the server to ignore the mysql.plugin table). --plugin-load, --plugin-load-add, and --early-plugin-load also enable plugins to be loaded at startup that cannot be loaded at runtime.

The --plugin-load-add option complements the --plugin-load option:

For example, these options:

--plugin-load=x --plugin-load-add=y

are equivalent to this option:

--plugin-load="x;y"

But these options:

--plugin-load-add=y --plugin-load=x

are equivalent to this option:

--plugin-load=x

Plugins installed with the INSTALL PLUGIN statement:

A plugin located in a plugin library file can be loaded at runtime with the INSTALL PLUGIN statement. The statement also registers the plugin in the mysql.plugin table to cause the server to load it on subsequent restarts. For this reason, INSTALL PLUGIN requires the INSERT privilege for the mysql.plugin table.

The plugin library file base name depends on your platform. Common suffixes are .so for Unix and Unix-like systems, .dll for Windows.

Example: The --plugin-load option installs a plugin at server startup. To install a plugin named myplugin from a plugin library file named somepluglib.so, use these lines in a my.cnf file:

[mysqld]
plugin-load=myplugin=somepluglib.so

In this case, the plugin is not registered in mysql.plugin. Restarting the server without the --plugin-load option causes the plugin not to be loaded at startup.

Alternatively, the INSTALL PLUGIN statement causes the server to load the plugin code from the library file at runtime:

INSTALL PLUGIN myplugin SONAME 'somepluglib.so';

INSTALL PLUGIN also causes permanent plugin registration: The plugin is listed in the mysql.plugin table to ensure that the server loads it on subsequent restarts.

Many plugins can be loaded either at server startup or at runtime. However, if a plugin is designed such that it must be loaded and initialized during server startup, attempts to load it at runtime using INSTALL PLUGIN produce an error:

mysql> INSTALL PLUGIN myplugin SONAME 'somepluglib.so';
ERROR 1721 (HY000): Plugin 'myplugin' is marked as not dynamically
installable. You have to stop the server to install it.

In this case, you must use --plugin-load, --plugin-load-add, or --early-plugin-load.

If a plugin is named both using a --plugin-load, --plugin-load-add, or --early-plugin-load option and (as a result of an earlier INSTALL PLUGIN statement) in the mysql.plugin table, the server starts but writes these messages to the error log:

[ERROR] Function 'plugin_name' already exists
[Warning] Couldn't load plugin named 'plugin_name'
with soname 'plugin_object_file'.

Controlling Plugin Activation State

If the server knows about a plugin when it starts (for example, because the plugin is named using a --plugin-load option or is registered in the mysql.plugin table), the server loads and enables the plugin by default. It is possible to control activation state for such a plugin using a --plugin_name[=activation_state] startup option, where plugin_name is the name of the plugin to affect, such as innodb, csv, or validate_password. As with other options, dashes and underscores are interchangeable in option names. Also, activation state values are not case sensitive. For example, --my_plugin=ON and --my-plugin=on are equivalent.

  • --plugin_name=OFF

    Tells the server to disable the plugin. This may not be possible for certain built-in plugins, such as mysql_native_password.

  • --plugin_name[=ON]

    Tells the server to enable the plugin. (Specifying the option as --plugin_name without a value has the same effect.) If the plugin fails to initialize, the server runs with the plugin disabled.

  • --plugin_name=FORCE

    Tells the server to enable the plugin, but if plugin initialization fails, the server does not start. In other words, this option forces the server to run with the plugin enabled or not at all.

  • --plugin_name=FORCE_PLUS_PERMANENT

    Like FORCE, but in addition prevents the plugin from being unloaded at runtime. If a user attempts to do so with UNINSTALL PLUGIN, an error occurs.

Plugin activation states are visible in the LOAD_OPTION column of the INFORMATION_SCHEMA.PLUGINS table.

Suppose that CSV, BLACKHOLE, and ARCHIVE are built-in pluggable storage engines and that you want the server to load them at startup, subject to these conditions: The server is permitted to run if CSV initialization fails, must require that BLACKHOLE initialization succeeds, and should disable ARCHIVE. To accomplish that, use these lines in an option file:

[mysqld]
csv=ON
blackhole=FORCE
archive=OFF

The --enable-plugin_name option format is a synonym for --plugin_name=ON. The --disable-plugin_name and --skip-plugin_name option formats are synonyms for --plugin_name=OFF.

If a plugin is disabled, either explicitly with OFF or implicitly because it was enabled with ON but failed to initialize, aspects of server operation that require the plugin will change. For example, if the plugin implements a storage engine, existing tables for the storage engine become inaccessible, and attempts to create new tables for the storage engine result in tables that use the default storage engine unless the NO_ENGINE_SUBSTITUTION SQL mode is enabled to cause an error to occur instead.

Disabling a plugin may require adjustment to other options. For example, if you start the server using --skip-innodb to disable InnoDB, other innodb_xxx options likely will need to be omitted at startup. In addition, because InnoDB is the default storage engine, it will not start unless you specify another available storage engine with --default_storage_engine. You must also set --default_tmp_storage_engine.

Uninstalling Plugins

At runtime, the UNINSTALL PLUGIN statement disables and uninstalls a plugin known to the server. The statement unloads the plugin and removes it from the mysql.plugin table, if it is registered there. For this reason, UNINSTALL PLUGIN statement requires the DELETE privilege for the mysql.plugin table. With the plugin no longer registered in the table, the server will not load the plugin automatically for subsequent restarts.

UNINSTALL PLUGIN can unload a plugin regardless of whether it was loaded at runtime with INSTALL PLUGIN or at startup with a plugin-loading option, subject to these conditions:

  • It cannot unload plugins that are built in to the server. These can be identified as those that have a library name of NULL in the output from INFORMATION_SCHEMA.PLUGINS or SHOW PLUGINS.

  • It cannot unload plugins for which the server was started with --plugin_name=FORCE_PLUS_PERMANENT, which prevents plugin unloading at runtime. These can be identified from the LOAD_OPTION column of the INFORMATION_SCHEMA.PLUGINS table.

To uninstall a plugin that currently is loaded at server startup with a plugin-loading option, use this procedure.

  1. Remove any options related to the plugin from the my.cnf file.

  2. Restart the server.

  3. Plugins normally are installed using either a plugin-loading option at startup or with INSTALL PLUGIN at runtime, but not both. However, removing options for a plugin from the my.cnf file may not be sufficient to uninstall it if at some point INSTALL PLUGIN has also been used. If the plugin still appears in the output from INFORMATION_SCHEMA.PLUGINS or SHOW PLUGINS, use UNINSTALL PLUGIN to remove it from the mysql.plugin table. Then restart the server again.

6.5.3 Obtaining Server Plugin Information

There are several ways to determine which plugins are installed in the server:

  • The INFORMATION_SCHEMA.PLUGINS table contains a row for each loaded plugin. Any that have a PLUGIN_LIBRARY value of NULL are built in and cannot be unloaded.

    mysql> SELECT * FROM information_schema.PLUGINS\G
    *************************** 1. row ***************************
               PLUGIN_NAME: binlog
            PLUGIN_VERSION: 1.0
             PLUGIN_STATUS: ACTIVE
               PLUGIN_TYPE: STORAGE ENGINE
       PLUGIN_TYPE_VERSION: 50158.0
            PLUGIN_LIBRARY: NULL
    PLUGIN_LIBRARY_VERSION: NULL
             PLUGIN_AUTHOR: MySQL AB
        PLUGIN_DESCRIPTION: This is a pseudo storage engine to represent the binlog in a transaction
            PLUGIN_LICENSE: GPL
               LOAD_OPTION: FORCE
    ...
    *************************** 10. row ***************************
               PLUGIN_NAME: InnoDB
            PLUGIN_VERSION: 1.0
             PLUGIN_STATUS: ACTIVE
               PLUGIN_TYPE: STORAGE ENGINE
       PLUGIN_TYPE_VERSION: 50158.0
            PLUGIN_LIBRARY: ha_innodb_plugin.so
    PLUGIN_LIBRARY_VERSION: 1.0
             PLUGIN_AUTHOR: Innobase Oy
        PLUGIN_DESCRIPTION: Supports transactions, row-level locking,
                            and foreign keys
            PLUGIN_LICENSE: GPL
               LOAD_OPTION: ON
    ...
    
  • The SHOW PLUGINS statement displays a row for each loaded plugin. Any that have a Library value of NULL are built in and cannot be unloaded.

    mysql> SHOW PLUGINS\G
    *************************** 1. row ***************************
       Name: binlog
     Status: ACTIVE
       Type: STORAGE ENGINE
    Library: NULL
    License: GPL
    ...
    *************************** 10. row ***************************
       Name: InnoDB
     Status: ACTIVE
       Type: STORAGE ENGINE
    Library: ha_innodb_plugin.so
    License: GPL
    ...
    
  • The mysql.plugin table shows which plugins have been registered with INSTALL PLUGIN. The table contains only plugin names and library file names, so it does not provide as much information as the PLUGINS table or the SHOW PLUGINS statement.

6.5.4 MySQL Enterprise Thread Pool

Note

MySQL Enterprise Thread Pool is an extension included in MySQL Enterprise Edition, a commercial product. To learn more about commercial products, http://www.mysql.com/products/.

As of MySQL 5.7.9, MySQL Enterprise Edition includes MySQL Enterprise Thread Pool, implemented using a server plugin. The default thread-handling model in MySQL Server executes statements using one thread per client connection. As more clients connect to the server and execute statements, overall performance degrades. The thread pool plugin provides an alternative thread-handling model designed to reduce overhead and improve performance. The plugin implements a thread pool that increases server performance by efficiently managing statement execution threads for large numbers of client connections.

The thread pool addresses several problems of the one thread per connection model:

  • Too many thread stacks make CPU caches almost useless in highly parallel execution workloads. The thread pool promotes thread stack reuse to minimize the CPU cache footprint.

  • With too many threads executing in parallel, context switching overhead is high. This also presents a challenging task to the operating system scheduler. The thread pool controls the number of active threads to keep the parallelism within the MySQL server at a level that it can handle and that is appropriate for the server host on which MySQL is executing.

  • Too many transactions executing in parallel increases resource contention. In InnoDB, this increases the time spent holding central mutexes. The thread pool controls when transactions start to ensure that not too many execute in parallel.

The thread pool plugin is included only in MySQL Enterprise Edition. It is not included in MySQL community distributions.

On Windows, the thread pool plugin requires Windows Vista or newer. On Linux, the plugin requires kernel 2.6.9 or higher.

Additional Resources

Section A.14, “MySQL 5.7 FAQ: MySQL Enterprise Thread Pool”

6.5.4.1 Thread Pool Components

The thread pool feature comprises these components:

6.5.4.2 Thread Pool Installation

This section describes how to install MySQL Enterprise Thread Pool. For general information about installing plugins, see Section 6.5.2, “Installing and Uninstalling Plugins”.

To be usable by the server, the plugin library file must be located in the MySQL plugin directory (the directory named by the plugin_dir system variable). If necessary, set the value of plugin_dir at server startup to tell the server the plugin directory location.

The plugin library file base name is thread_pool. The file name suffix differs per platform (for example, .so for Unix and Unix-like systems, .dll for Windows).

To enable thread pool capability, load the plugins to be used by starting the server with the --plugin-load option. For example, if you name just the plugin library file, the server loads all plugins that it contains (that is, the thread pool plugin and all the INFORMATION_SCHEMA tables). To do this, put these lines in your my.cnf file (adjust the .so suffix for your platform as necessary):

[mysqld]
plugin-load=thread_pool.so

That is equivalent to loading all thread pool plugins by naming them individually:

[mysqld]
plugin-load=thread_pool=thread_pool.so;tp_thread_state=thread_pool.so;tp_thread_group_state=thread_pool.so;tp_thread_group_stats=thread_pool.so

With --plugin-load, all plugins must be named on a single line. To make the option file easier to read, use --plugin-load-add, which enables naming plugins individually:

[mysqld]
plugin-load-add=thread_pool=thread_pool.so
plugin-load-add=tp_thread_state=thread_pool.so
plugin-load-add=tp_thread_group_state=thread_pool.so
plugin-load-add=tp_thread_group_stats=thread_pool.so

If desired, you can load individual plugins from the library file. To load the thread pool plugin but not the INFORMATION_SCHEMA tables, use an option like this:

[mysqld]
plugin-load=thread_pool=thread_pool.so

To load the thread pool plugin and only the TP_THREAD_STATE INFORMATION_SCHEMA table, use an option like this:

[mysqld]
plugin-load=thread_pool=thread_pool.so;tp_thread_state=thread_pool.so
Note

If you do not load all the INFORMATION_SCHEMA tables, some or all MySQL Enterprise Monitor thread pool graphs will be empty.

To verify plugin installation, examine the INFORMATION_SCHEMA.PLUGINS table or use the SHOW PLUGINS statement (see Section 6.5.3, “Obtaining Server Plugin Information”). For example:

mysql> SELECT PLUGIN_NAME, PLUGIN_STATUS FROM INFORMATION_SCHEMA.PLUGINS
    -> WHERE PLUGIN_NAME LIKE 'thread%' OR PLUGIN_NAME LIKE 'tp%';
+-----------------------+---------------+
| PLUGIN_NAME           | PLUGIN_STATUS |
+-----------------------+---------------+
| thread_pool           | ACTIVE        |
| TP_THREAD_STATE       | ACTIVE        |
| TP_THREAD_GROUP_STATE | ACTIVE        |
| TP_THREAD_GROUP_STATS | ACTIVE        |
+-----------------------+---------------+

If the server loads the thread pool plugin successfully, it sets the thread_handling system variable to dynamically-loaded. If the plugin fails to load, the server writes a message to the error log.

6.5.4.3 Thread Pool Operation

The thread pool consists of a number of thread groups, each of which manages a set of client connections. As connections are established, the thread pool assigns them to thread groups in round-robin fashion.

The number of thread groups is configurable using the thread_pool_size system variable. The default number of groups is 16. For guidelines on setting this variable, see Section 6.5.4.4, “Thread Pool Tuning”.

The maximum number of threads per group is 4096 (or 4095 on some systems where one thread is used internally).

The thread pool separates connections and threads, so there is no fixed relationship between connections and the threads that execute statements received from those connections. This differs from the default thread-handling model that associates one thread with one connection such that the thread executes all statements from the connection.

The thread pool tries to ensure a maximum of one thread executing in each group at any time, but sometimes permits more threads to execute temporarily for best performance. The algorithm works in the following manner:

  • Each thread group has a listener thread that listens for incoming statements from the connections assigned to the group. When a statement arrives, the thread group either begins executing it immediately or queues it for later execution:

    • Immediate execution occurs if the statement is the only one received and no statements are queued or currently executing.

    • Queuing occurs if the statement cannot begin executing immediately.

  • If immediate execution occurs, execution is performed by the listener thread. (This means that temporarily no thread in the group is listening.) If the statement finishes quickly, the executing thread returns to listening for statements. Otherwise, the thread pool considers the statement stalled and starts another thread as a listener thread (creating it if necessary). To ensure that no thread group becomes blocked by stalled statements, the thread pool has a background thread that regularly monitors thread group states.

    By using the listening thread to execute a statement that can begin immediately, there is no need to create an additional thread if the statement finishes quickly. This ensures the most efficient execution possible in the case of a low number of concurrent threads.

    When the thread pool plugin starts, it creates one thread per group (the listener thread), plus the background thread. Additional threads are created as necessary to execute statements.

  • The value of the thread_pool_stall_limit system variable determines the meaning of finishes quickly in the previous item. The default time before threads are considered stalled is 60ms but can be set to a maximum of 6s. This parameter is configurable to enable you to strike a balance appropriate for the server work load. Short wait values permit threads to start more quickly. Short values are also better for avoiding deadlock situations. Long wait values are useful for workloads that include long-running statements, to avoid starting too many new statements while the current ones execute.

  • The thread pool focuses on limiting the number of concurrent short-running statements. Before an executing statement reaches the stall time, it prevents other statements from beginning to execute. If the statement executes past the stall time, it is permitted to continue but no longer prevents other statements from starting. In this way, the thread pool tries to ensure that in each thread group there is never more than one short-running statement, although there might be multiple long-running statements. It is undesirable to let long-running statements prevent other statements from executing because there is no limit on the amount of waiting that might be necessary. For example, on a replication master, a thread that is sending binary log events to a slave effectively runs forever.

  • A statement becomes blocked if it encounters a disk I/O operation or a user level lock (row lock or table lock). The block would cause the thread group to become unused, so there are callbacks to the thread pool to ensure that the thread pool can immediately start a new thread in this group to execute another statement. When a blocked thread returns, the thread pool permits it to restart immediately.

  • There are two queues, a high-priority queue and a low-priority queue. The first statement in a transaction goes to the low-priority queue. Any following statements for the transaction go to the high-priority queue if the transaction is ongoing (statements for it have begun executing), or to the low-priority queue otherwise. Queue assignment can be affected by enabling the thread_pool_high_priority_connection system variable, which causes all queued statements for a session to go into the high-priority queue.

    Statements for a nontransactional storage engine, or a transactional engine if autocommit is enabled, are treated as low-priority statements because in this case each statement is a transaction. Thus, given a mix of statements for InnoDB and MyISAM tables, the thread pool prioritizes those for InnoDB over those for MyISAM unless autocommit is enabled. With autocommit enabled, all statements will be low priority.

  • When the thread group selects a queued statement for execution, it first looks in the high-priority queue, then in the low-priority queue. If a statement is found, it is removed from its queue and begins to execute.

  • If a statement stays in the low-priority queue too long, the thread pool moves to the high-priority queue. The value of the thread_pool_prio_kickup_timer system variable controls the time before movement. For each thread group, a maximum of one statement per 10ms or 100 per second will be moved from the low-priority queue to the high-priority queue.

  • The thread pool reuses the most active threads to obtain a much better use of CPU caches. This is a small adjustment that has a great impact on performance.

  • While a thread executes a statement from a user connection, Performance Schema instrumentation accounts thread activity to the user connection. Otherwise, Performance Schema accounts activity to the thread pool.

Here are examples of conditions under which a thread group might have multiple threads started to execute statements:

  • One thread begins executing a statement, but runs long enough to be considered stalled. The thread group permits another thread to begin executing another statement even through the first thread is still executing.

  • One thread begins executing a statement, then becomes blocked and reports this back to the thread pool. The thread group permits another thread to begin executing another statement.

  • One thread begins executing a statement, becomes blocked, but does not report back that it is blocked because the block does not occur in code that has been instrumented with thread pool callbacks. In this case, the thread appears to the thread group to be still running. If the block lasts long enough for the statement to be considered stalled, the group permits another thread to begin executing another statement.

The thread pool is designed to be scalable across an increasing number of connections. It is also designed to avoid deadlocks that can arise from limiting the number of actively executing statements. It is important that threads that do not report back to the thread pool do not prevent other statements from executing and thus cause the thread pool to become deadlocked. Examples of such statements follow:

  • Long-running statements. These would lead to all resources used by only a few statements and they could prevent all others from accessing the server.

  • Binary log dump threads that read the binary log and send it to slaves. This is a kind of long-running statement that runs for a very long time, and that should not prevent other statements from executing.

  • Statements blocked on a row lock, table lock, sleep, or any other blocking activity that has not been reported back to the thread pool by MySQL Server or a storage engine.

In each case, to prevent deadlock, the statement is moved to the stalled category when it does not complete quickly, so that the thread group can permit another statement to begin executing. With this design, when a thread executes or becomes blocked for an extended time, the thread pool moves the thread to the stalled category and for the rest of the statement's execution, it does not prevent other statements from executing.

The maximum number of threads that can occur is the sum of max_connections and thread_pool_size. This can happen in a situation where all connections are in execution mode and an extra thread is created per group to listen for more statements. This is not necessarily a state that happens often, but it is theoretically possible.

6.5.4.4 Thread Pool Tuning

This section provides guidelines on setting thread pool system variables for best performance, measured using a metric such as transactions per second.

thread_pool_size is the most important parameter controlling thread pool performance. It can be set only at server startup. Our experience in testing the thread pool indicates the following:

  • If the primary storage engine is InnoDB, the optimal thread_pool_size setting is likely to be between 16 and 36, with the most common optimal values tending to be from 24 to 36. We have not seen any situation where the setting has been optimal beyond 36. There may be special cases where a value smaller than 16 is optimal.

    For workloads such as DBT2 and Sysbench, the optimum for InnoDB seems to be usually around 36. For very write-intensive workloads, the optimal setting can sometimes be lower.

  • If the primary storage engine is MyISAM, the thread_pool_size setting should be fairly low. We tend to get optimal performance for values from 4 to 8. Higher values tend to have a slightly negative but not dramatic impact on performance.

Another system variable, thread_pool_stall_limit, is important for handling of blocked and long-running statements. If all calls that block the MySQL Server are reported to the thread pool, it would always know when execution threads are blocked. However, this may not always be true. For example, blocks could occur in code that has not been instrumented with thread pool callbacks. For such cases, the thread pool must be able to identify threads that appear to be blocked. This is done by means of a timeout, the length of which can be tuned using the thread_pool_stall_limit system variable. This parameter ensures that the server does not become completely blocked. The value of thread_pool_stall_limit has an upper limit of 6 seconds to prevent the risk of a deadlocked server.

thread_pool_stall_limit also enables the thread pool to handle long-running statements. If a long-running statement was permitted to block a thread group, all other connections assigned to the group would be blocked and unable to start execution until the long-running statement completed. In the worst case, this could take hours or even days.

The value of thread_pool_stall_limit should be chosen such that statements that execute longer than its value are considered stalled. Stalled statements generate a lot of extra overhead since they involve extra context switches and in some cases even extra thread creations. On the other hand, setting the thread_pool_stall_limit parameter too high means that long-running statements will block a number of short-running statements for longer than necessary. Short wait values permit threads to start more quickly. Short values are also better for avoiding deadlock situations. Long wait values are useful for workloads that include long-running statements, to avoid starting too many new statements while the current ones execute.

Suppose a server executes a workload where 99.9% of the statements complete within 100ms even when the server is loaded, and the remaining statements take between 100ms and 2 hours fairly evenly spread. In this case, it would make sense to set thread_pool_stall_limit to 10 (meaning 100ms). The default value of 60ms is okay for servers that primarily execute very simple statements.

The thread_pool_stall_limit parameter can be changed at runtime to enable you to strike a balance appropriate for the server work load. Assuming that the TP_THREAD_GROUP_STATS table is enabled, you can use the following query to determine the fraction of executed statements that stalled:

SELECT SUM(STALLED_QUERIES_EXECUTED) / SUM(QUERIES_EXECUTED)
FROM information_schema.TP_THREAD_GROUP_STATS;

This number should be as low as possible. To decrease the likelihood of statements stalling, increase the value of thread_pool_stall_limit.

When a statement arrives, what is the maximum time it can be delayed before it actually starts executing? Suppose that the following conditions apply:

In the worst case, the 10 high-priority statements represent 10 transactions that continue executing for a long time. Thus, in the worst case, no statements will be moved to the high-priority queue because it will always already contain statements awaiting execution. After 10 seconds, the new statement is eligible to be moved to the high-priority queue. However, before it can be moved, all the statements before it must be moved as well. This could take another 2 seconds because a maximum of 100 statements per second are moved to the high-priority queue. Now when the statement reaches the high-priority queue, there could potentially be many long-running statements ahead of it. In the worst case, every one of those will become stalled and it will take 1 second for each statement before the next statement is retrieved from the high-priority queue. Thus, in this scenario, it will take 222 seconds before the new statement starts executing.

This example shows a worst case for an application. How to handle it depends on the application. If the application has high requirements for the response time, it should most likely throttle users at a higher level itself. Otherwise, it can use the thread pool configuration parameters to set some kind of a maximum waiting time.

6.5.5 The Rewriter Query Rewrite Plugin

As of MySQL 5.7.6, MySQL Server supports query rewrite plugins that can examine and possibly modify statements received by the server before the server executes them. See Query Rewrite Plugins.

MySQL distributions include a postparse query rewrite plugin named Rewriter and scripts for installing the plugin and its associated components. These components work together to provide SELECT rewriting capability:

  • A server-side plugin named Rewriter examines SELECT statements and may rewrite them, based on its in-memory cache of rewrite rules. Standalone SELECT statements and SELECT statements in prepared statements are subject to rewriting. SELECT statements occurring within view definitions or stored programs are not subject to rewriting.

  • The Rewriter plugin uses a database named query_rewrite containing a table named rewrite_rules. The table provides persistent storage for the rules that the plugin uses to decide whether to rewrite statements. Users communicate with the plugin by modifying the set of rules stored in this table. The plugin communicates with users by setting the message column of table rows.

  • The query_rewrite database contains a stored procedure named flush_rewrite_rules() that loads the contents of the rules table into the plugin.

  • A user-defined function named load_rewrite_rules() is used by the flush_rewrite_rules() stored procedure.

  • The Rewriter plugin exposes system variables that enable plugin configuration and status variables that provide runtime operational information.

The following sections describe how to install and use the Rewriter plugin, and provide reference information for its associated components.

6.5.5.1 Installing or uninstalling the Rewriter Query Rewrite Plugin

Note

If installed, the Rewriter plugin involves some overhead even when disabled. To avoid this overhead, do not install the plugin unless you plan to use it.

To install or uninstall the Rewriter query rewrite plugin, choose the approropriate script located in the share directory of your MySQL installation:

  • install_rewriter.sql: Choose this script to install the Rewriter plugin and its associated components.

    Note

    Before MySQL 5.7.8, there are two installation scripts, install_rewriter.sql and install_rewriter_with_optional_columns.sql, which differ in whether they create the pattern_digest and normalized_columns columns of the rewrite_rules table. As of 5.7.8, the installation script always creates these columns. (For details about the table columns, see Section 6.5.5.3.1, “Rewriter Query Rewrite Plugin Rules Table”.)

  • uninstall_rewriter.sql: Choose this script to uninstall the Rewriter plugin and its associated components.

Run the chosen script as follows:

shell> mysql -u root -p < install_rewriter.sql
Enter password: (enter root password here)

The example here uses the install_rewriter.sql installation script. Make the appropriate substitution if you choose a different script.

Running an installation script should install and enable the plugin. To verify that, connect to the server and execute this statement:

mysql> SHOW GLOBAL VARIABLES LIKE 'rewriter_enabled';
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| rewriter_enabled | ON    |
+------------------+-------+

For usage instructions, see Section 6.5.5.2, “Using the Rewriter Query Rewrite Plugin”. For reference information, see Section 6.5.5.3, “Rewriter Query Rewrite Plugin Reference”.

6.5.5.2 Using the Rewriter Query Rewrite Plugin

To enable or disable the plugin, enable or disable the rewriter_enabled system variable. By default, the Rewriter plugin is enabled when you install it (see Section 6.5.5.1, “Installing or uninstalling the Rewriter Query Rewrite Plugin”). To set the initial plugin state explicitly, you can set the variable at server startup. For example, to enable the plugin in an option file, use these lines:

[mysqld]
rewriter_enabled=ON

It is also possible to enable or disable the plugin at runtime:

mosql> SET GLOBAL rewriter_enabled = ON;
mysql> SET GLOBAL rewriter_enabled = OFF;

Assuming that the Rewriter plugin is enabled, it examines and possibly modifies each SELECT statement received by the server. The plugin determines whether to rewrite statements based on its in-memory cache of rewriting rules, which are loaded from the rewrite_rules table in the query_rewrite database.

Adding Rewrite Rules

To add rules for the Rewriter plugin, add rows to the rewrite_rules table, then invoke the flush_rewrite_rules() stored procedure to load the rules from the table into the plugin. The following example creates a simple rule to match statements that select a single literal value:

mysql> INSERT INTO query_rewrite.rewrite_rules (pattern, replacement)
    -> VALUES('SELECT ?', 'SELECT ? + 1');

The resulting table contents look like this:

mysql> SELECT * FROM query_rewrite.rewrite_rules\G
*************************** 1. row ***************************
                id: 1
           pattern: SELECT ?
  pattern_database: NULL
       replacement: SELECT ? + 1
           enabled: YES
           message: NULL
    pattern_digest: NULL
normalized_pattern: NULL

The rule specifies a pattern template indicating which SELECT statements to match, and a replacement template indicating how to rewrite matching statements. However, adding the rule to the rewrite_rules table is not sufficient to cause the Rewriter plugin to use the rule. You must invoke flush_rewrite_rules() to load the table contents into the plugin in-memory cache:

mysql> CALL query_rewrite.flush_rewrite_rules();
Tip

If your rewrite rules seem not to be working properly, make sure that you have reloaded the rules table by calling flush_rewrite_rules().

When the plugin reads each rule from the rules table, it computes a normalized form (digest) from the pattern and a digest hash value, and updates the normalized_pattern and pattern_digest columns:

mysql> SELECT * FROM query_rewrite.rewrite_rules\G
*************************** 1. row ***************************
                id: 1
           pattern: SELECT ?
  pattern_database: NULL
       replacement: SELECT ? + 1
           enabled: YES
           message: NULL
    pattern_digest: 46b876e64cd5c41009d91c754921f1d4
normalized_pattern: select ?

For information about statement digesting and normalized statements, see Section 25.8, “Performance Schema Statement Digests”.

Patterns use the same syntax as prepared statements (see Section 14.5.1, “PREPARE Syntax”). Within a pattern template, ? characters act as parameter markers that match data values. Parameter markers can be used only where data values should appear, not for SQL keywords, identifiers, and so forth. The ? characters should not be enclosed within quotation marks.

Like the pattern, the replacement can contain ? characters. For a statement that matches a pattern template, the plugin rewrites it, replacing ? parameter markers in the replacement using data values matched by the corresponding markers in the pattern. The result is a complete statement string. The plugin asks the server to parse it, and returns the result to the server as the representation of the rewritten statement.

After adding and loading the rule, check whether rewriting occurs according to whether statements match the rule pattern:

mysql> SELECT PI();
+----------+
| PI()     |
+----------+
| 3.141593 |
+----------+
1 row in set (0.01 sec)

mysql> SELECT 10;
+--------+
| 10 + 1 |
+--------+
|     11 |
+--------+
1 row in set, 1 warning (0.00 sec)

No rewriting occurs for the first SELECT statement, but does for the second. The second statement illustrates that when the Rewriter plugin rewrites a statement, it produces a warning message. To view the message, use SHOW WARNINGS:

mysql> SHOW WARNINGS\G
*************************** 1. row ***************************
  Level: Note
   Code: 1105
Message: Query 'SELECT 10' rewritten to 'SELECT 10 + 1' by a query rewrite plugin

To enable or disable an existing rule, modify its enabled column and reload the table into the plugin. To disable rule 1:

mysql> UPDATE query_rewrite.rewrite_rules SET enabled = 'NO' WHERE id = 1;
mysql> CALL query_rewrite.flush_rewrite_rules();

This enables you to deactivate a rule without removing it from the table.

To re-enable rule 1:

mysql> UPDATE query_rewrite.rewrite_rules SET enabled = 'YES' WHERE id = 1;
mysql> CALL query_rewrite.flush_rewrite_rules();

The rewrite_rules table contains a pattern_database column that Rewriter uses for matching table names that are not qualified with a database name:

  • Qualified table names in statements match qualified names in the pattern if corresponding database and table names are identical.

  • Unqualified table names in statements match unqualified names in the pattern only if the default database is the same as pattern_database and the table names are identical.

Suppose that a table named appdb.users has a column named id and that applications are expected to select rows from the table using a query of one of these forms, where the second can be used only if appdb is the default database:

SELECT * FROM users WHERE appdb.id = id_value;
SELECT * FROM users WHERE id = id_value;

Suppose also that the id column is renamed to user_id (perhaps the table must be modified to add another type of ID and it is necessary to indicate more specifically what type of ID the id column represents).

The change means that applications must refer to user_id rather than id in the WHERE clause. But if there are old applications that cannot be written to change the SELECT queries they generate, they will no longer work properly. The Rewriter plugin can solve this problem. To match and rewrite statements whether or not they qualify the table name, add the following two rules and reload the rules table:

mysql> INSERT INTO query_rewrite.rewrite_rules
    -> (pattern, replacement) VALUES(
    -> 'SELECT * FROM appdb.users WHERE id = ?',
    -> 'SELECT * FROM appdb.users WHERE user_id = ?'
    -> );
mysql> INSERT INTO query_rewrite.rewrite_rules
    -> (pattern, replacement, pattern_database) VALUES(
    -> 'SELECT * FROM users WHERE id = ?',
    -> 'SELECT * FROM users WHERE user_id = ?',
    -> 'appdb'
    -> );
mysql> CALL query_rewrite.flush_rewrite_rules();

Rewriter uses the first rule to match statements that use the qualified table name. It uses the second to match statements that used the unqualified name, but only if the default database is appdb (the value in pattern_database).

How Statement Matching Works

The Rewriter plugin uses statement digests to match incoming statements against rewrite rules in stages. The max_digest_length system variable determines the size of the buffer used for computing statement digests. Larger values enable computation of digests that distinguish longer statements. Smaller values use less memory but increase the likelihood of longer statements colliding with the same digest value.

The plugin matches each statement to the rewrite rules as follows:

  1. Compute the statement digest hash value and compare it to the rule digest hash values. This is subject to false positives, but serves as a quick rejection test.

  2. If the statement digest hash value matches any pattern digest hash values, match the normalized form of the statement to the normalized form of the matching rule patterns.

  3. If the normalized statement matches a rule, compare the literal values in the statement and the pattern. A ? in the pattern matches any literal value in the statement. If the statement prepares a SELECT statement, ? in the pattern also matches ? in the statement. Otherwise, corresponding literals must be the same.

If multiple rules match a statement, it is indeterminate which one the plugin uses to rewrite the statement.

If a pattern contains more markers than the replacement, the plugin discards excess data values. If a pattern contains fewer markers than the replacement, it is an error. The plugin notices this when the rules table is loaded, writes an error message to the message column of the rule row to communicate the problem, and sets the Rewriter_reload_error status variable to ON.

Rewriting Prepared Statements

Prepared statements are rewritten at parse time (that is, when they are prepared), not when they are executed later.

Prepared statements differ from nonprepared statements in that they may contain ? characters as parameter markers. To match a ? in a prepared statement, a Rewriter pattern must contain ? in the same location. Suppose that a rewrite rule has this pattern:

SELECT ?, 3

The following table shows several prepared SELECT statements and whether the rule pattern matches them.

Prepared StatementWhether Pattern Matches Statement
PREPARE s AS 'SELECT 3, 3'Yes
PREPARE s AS 'SELECT ?, 3'Yes
PREPARE s AS 'SELECT 3, ?'No
PREPARE s AS 'SELECT ?, ?'No
Rewriter Plugin Operational Information

The Rewriter plugin makes information available about its operation by means of several status variables:

mysql> SHOW GLOBAL STATUS LIKE 'Rewriter%';
+-----------------------------------+-------+
| Variable_name                     | Value |
+-----------------------------------+-------+
| Rewriter_number_loaded_rules      | 1     |
| Rewriter_number_reloads           | 5     |
| Rewriter_number_rewritten_queries | 1     |
| Rewriter_reload_error             | ON    |
+-----------------------------------+-------+

For descriptions of these variables, see Section 6.5.5.3.4, “Rewriter Query Rewrite Plugin Status Variables”.

When you load the rules table by calling the flush_rewrite_rules() stored procedure, if an error occurs for some rule, the CALL statement produces an error, and the plugin sets the Rewriter_reload_error status variable to ON:

mysql> CALL query_rewrite.flush_rewrite_rules();
ERROR 1644 (45000): Loading of some rule(s) failed.

mysql> SHOW GLOBAL STATUS LIKE 'Rewriter_reload_error';
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| Rewriter_reload_error | ON    |
+-----------------------+-------+

In this case, check the message column of rewrite_rules table rows for non-NULL values to see what the problem was.

Rewriter Plugin Use of Character Sets

When the rewrite_rules table is loaded into the Rewriter plugin, the plugin interprets statements using the current global value of the character_set_client system variable. If the global character_set_client value is changed subsequently, the rules table must be reloaded.

A client must have a session character_set_client value identical to what the global value was when the rules table was loaded or rule matching will not work for that client.

6.5.5.3 Rewriter Query Rewrite Plugin Reference

The following discussion serves as a reference to these components associated with the Rewriter query rewrite plugin:

  • The Rewriter rules table in the query_rewrite database

  • Rewriter procedures and functions

  • Rewriter system and status variables

6.5.5.3.1 Rewriter Query Rewrite Plugin Rules Table

The rewrite_rules table in the query_rewrite database provides persistent storage for the rules that the Rewriter plugin uses to decide whether to rewrite statements.

Users communicate with the plugin by modifying the set of rules stored in this table. The plugin communicates with users by setting the table's message column.

Note

The rules table is loaded into the plugin by the flush_rewrite_rules stored procedure. Unless that procedure has been called following the most recent table modification, the table contents do not necessarily correspond to the set of rules the plugin is using.

The rewrite_rules table has these columns:

  • id

    The rule ID. This column is the table primary key. You can use the ID to uniquely identify any rule.

  • pattern

    The template that indicates the pattern for statements that the rule matches. Use ? to represent parameter markers that match data values.

  • pattern_database

    The database used to match unqualified table names in statements. Qualified table names in statements match qualified names in the pattern if corresponding database and table names are identical. Unqualified table names in statements match unqualified names in the pattern only if the default database is the same as pattern_database and the table names are identical.

  • replacement

    The template that indicates how to rewrite statements matching the pattern column value. Use ? to represent parameter markers that match data values. In rewritten statements, the plugin replaces ? parameter markers in replacement using data values matched by the corresponding markers in pattern.

  • enabled

    Whether the rule is enabled. Load operations (performed by invoking the flush_rewrite_rules() stored procedure) load the rule from the table into the Rewriter in-memory cache only if this column is YES (Y before MySQL 5.7.8).

    This column makes it possible to deactivate a rule without removing it: Set the column to a value other than YES and reload the table into the plugin.

  • message

    The plugin uses this column for communicating with users. If no error occurs when the rules table is loaded into memory, the plugin sets the message column to NULL. A non-NULL value indicates an error and the column contents are the error message. Errors can occur under these circumstances:

    • Either the pattern or the replacement is an incorrect SQL statement that produces syntax errors.

    • The replacement contains more ? parameter markers than the pattern.

    If a load error occurs, the plugin also sets the Rewriter_reload_error status variable to ON.

  • pattern_digest

    This column is used for debugging and diagnostics. If the column exists when the rules table is loaded into memory, the plugin updates it with the pattern digest. This column may be useful if you are trying to determine why some statement fails to be rewritten.

  • normalized_pattern

    This column is used for debugging and diagnostics. If the column exists when the rules table is loaded into memory, the plugin updates it with the normalized form of the pattern. This column may be useful if you are trying to determine why some statement fails to be rewritten.

Note

Before MySQL 5.7.8, the pattern_digest and normalized_pattern columns are optional: They are created if you install the Rewriter plugin using the install_rewriter_with_optional_columns.sql, but not if you use install_rewriter.sql.

6.5.5.3.2 Rewriter Query Rewrite Plugin Procedures and Functions

Rewriter plugin operation uses a stored procedure that loads the rules table into its in-memory cache, and a helper user-defined function (UDF). Under normal operation, users invoke only the stored procedure. The UDF is intended to be invoked by the stored procedure, not directly by users.

  • flush_rewrite_rules()

    This stored procedure uses the load_rewrite_rules() UDF to load the contents of the rewrite_rules table into the Rewriter in-memory cache. After loading the table, it also clears the query cache.

    Calling flush_rewrite_rules() implies COMMIT.

    Invoke this procedure after you modify the rules table to cause the plugin to update its cache from the new table contents. If any errors occur, the plugin sets the message column for the appropriate rule rows in the table and sets the Rewriter_reload_error status variable to ON.

  • load_rewrite_rules()

    This UDF is a helper routine used by the flush_rewrite_rules() stored procedure.

6.5.5.3.3 Rewriter Query Rewrite Plugin System Variables

The Rewriter query rewrite plugin supports the following system variables. These variables are available only if the plugin is installed (see Section 6.5.5.1, “Installing or uninstalling the Rewriter Query Rewrite Plugin”).

  • rewriter_enabled

    Introduced5.7.6
    System VariableNamerewriter_enabled
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultON

    Whether the Rewriter query rewrite plugin is enabled.

  • rewriter_verbose

    Introduced5.7.6
    System VariableNamerewriter_verbose
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger

    For internal use.

6.5.5.3.4 Rewriter Query Rewrite Plugin Status Variables

The Rewriter query rewrite plugin supports the following status variables. These variables are available only if the plugin is installed (see Section 6.5.5.1, “Installing or uninstalling the Rewriter Query Rewrite Plugin”).

  • Rewriter_number_loaded_rules

    The number of rewrite plugin rewrite rules successfully loaded from the rewrite_rules table into memory for use by the Rewriter plugin.

  • Rewriter_number_reloads

    The number of times the rewrite_rules table has been loaded into the in-memory cache used by the Rewriter plugin.

  • Rewriter_number_rewritten_queries

    The number of queries rewritten by the Rewriter query rewrite plugin since it was loaded.

  • Rewriter_reload_error

    Whether an error occurred the most recent time that the rewrite_rules table was loaded into the in-memory cache used by the Rewriter plugin. If the value is OFF, no error occurred. If the value is ON, an error occurred; check the message column of the rewriter_rules table for error messages.

6.5.6 Version Tokens

Distributions of MySQL 5.7.8 or higher include Version Tokens, a feature that enables creation of and synchronization around server tokens that applications can use to prevent accessing incorrect or out-of-date data.

The Version Tokens interface has these characteristics:

  • Version tokens are pairs consisting of a name that serves as a key or identifier, plus a value.

  • Version tokens can be locked. An application can use token locks to indicate to other cooperating applications that tokens are in use and should not be modified.

  • Version token lists are established per server; for example, to specify the server assignment or operational state. In addition, an application that communicates with a server can register its own list of tokens that indicate the state it requires the server to be in. An SQL statement sent by the application to a server not in the required state produces an error. This is a signal to the application that it should seek a different server in the required state to receive the SQL statement.

The following sections describe the components of Version Tokens, discuss how to install and use it, and provide reference information for its components.

6.5.6.1 Version Tokens Components

Version Tokens is based on a plugin library that implements these components:

  • A server-side plugin named version_tokens holds the list of version tokens associated with the server and subscribes to notifications for statement execution events. The version_tokens plugin uses the audit plugin API to monitor incoming statements from clients and matches each client's session-specific version token list against the server version token list. If there is a match, the plugin lets the statement through and the server continues to process it. Otherwise, the plugin returns an error to the client and the statement fails.

  • A set of user-defined functions (UDFs) provides an SQL-level API for manipulating and inspecting the list of server version tokens maintained by the plugin.

  • A system variable enables clients to specify the list of version tokens that register the required server state. If the server has a different state when a client sends a statement, the client receives an error.

6.5.6.2 Installing or Uninstalling Version Tokens

Note

If installed, Version Tokens involves some overhead. To avoid this overhead, do not install it unless you plan to use it.

This section describes how to install or uninstall Version Tokens, which is implemented in a plugin library file containing a plugin and user-defined functions. For general information about installing or uninstalling plugins and UDFs, see Section 6.5.2, “Installing and Uninstalling Plugins”, and Section 28.4.2.5, “UDF Compiling and Installing”.

To be usable by the server, the plugin library file must be located in the MySQL plugin directory (the directory named by the plugin_dir system variable). If necessary, set the value of plugin_dir at server startup to tell the server the plugin directory location.

The plugin library file base name is version_tokens. The file name suffix differs per platform (for example, .so for Unix and Unix-like systems, .dll for Windows).

To install the Version Tokens plugin and UDFs, use the INSTALL PLUGIN and CREATE FUNCTION statements (adjust the .so suffix for your platform as necessary):

INSTALL PLUGIN version_tokens SONAME 'version_token.so';
CREATE FUNCTION version_tokens_set RETURNS STRING SONAME 'version_token.so';
CREATE FUNCTION version_tokens_show RETURNS STRING SONAME 'version_token.so';
CREATE FUNCTION version_tokens_edit RETURNS STRING SONAME 'version_token.so';
CREATE FUNCTION version_tokens_delete RETURNS STRING SONAME 'version_token.so';
CREATE FUNCTION version_tokens_lock_shared RETURNS INT SONAME 'version_token.so';
CREATE FUNCTION version_tokens_lock_exclusive RETURNS INT SONAME 'version_token.so';
CREATE FUNCTION version_tokens_unlock RETURNS INT SONAME 'version_token.so';

You must install the UDFs to manage the server's version token list, but you must also install the plugin because the UDFs will not work correctly without it.

If the plugin and UDFs are used on a master replication server, install them on all slave servers as well to avoid replication problems.

Once installed as just described, the Version Tokens plugin and UDFs remain installed until uninstalled. To remove them, use the UNINSTALL PLUGIN and DROP FUNCTION statements:

UNINSTALL PLUGIN version_tokens;
DROP FUNCTION version_tokens_set;
DROP FUNCTION version_tokens_show;
DROP FUNCTION version_tokens_edit;
DROP FUNCTION version_tokens_delete;
DROP FUNCTION version_tokens_lock_shared;
DROP FUNCTION version_tokens_lock_exclusive;
DROP FUNCTION version_tokens_unlock;

6.5.6.3 Using Version Tokens

Before using Version Tokens, install it according to the instructions provided at Section 6.5.6.2, “Installing or Uninstalling Version Tokens”.

A scenario in which Version Tokens can be useful is a system that accesses a collection of MySQL servers but needs to manage them for load balancing purposes by monitoring them and adjusting server assignments according to load changes. Such a system comprises these components:

  • The collection of MySQL servers to be managed.

  • An administrative or management application that communicates with the servers and organizes them into high-availability groups. Groups serve different purposes, and servers within each group may have different assignments. Assignment of a server within a certain group can change at any time.

  • Client applications that access the servers to retrieve and update data, choosing servers according to the purposes assigned them. For example, a client should not send an update to a read-only server.

Version Tokens permit server access to be managed according to assignment without requiring clients to repeatedly query the servers about their assignments:

  • The management application performs server assignments and establishes version tokens on each server to reflect its assignment. The application caches this information to provide a central access point to it.

    If at some point the management application needs to change a server assignment (for example, to change it from permitting writes to read only), it changes the server's version token list and updates its cache.

  • To improve performance, client applications obtain cache information from the management application, enabling them to avoid having to retrieve information about server assignments for each statement. Based on the type of statements it will issue (for example, reads versus writes), a client selects an appropriate server and connects to it.

  • In addition, the client sends to the server its own client-specific version tokens to register the assignment it requires of the server. For each statement sent by the client to the server, the server compares its own token list with the client token list. If the server token list contains all tokens present in the client token list with the same values, there is a match and the server executes the statement.

    On the other hand, perhaps the management application has changed the server assignment and its version token list. In this case, the new server assignment may now be incompatible with the client requirements. A token mismatch between the server and client token lists occurs and the server returns an error in reply to the statement. This is an indication to the client to refresh its version token information from the management application cache, and to select a new server to communicate with.

The client-side logic for detecting version token errors and selecting a new server can be implemented different ways:

  • The client can handle all version token registration, mismatch detection, and connection switching itself.

  • The logic for those actions can be implemented in a connector that manages connections between clients and MySQL servers. Such a connector might handle mismatch error detection and statement resending itself, or it might pass the error to the application and leave it to the application to resend the statement.

The following example illustrates the preceding discussion in more concrete form.

When Version Tokens initializes on a given server, the server's version token list is empty. Token list maintenance is performed by calling user-defined functions (UDFs). The SUPER privilege is required to call any of the Version Token UDFs, so token list modification is expected to be done by a management or administrative application that has that privilege.

Suppose that a management application communicates with a set of servers that are queried by clients to access employee and product databases (named emp and prod, respectively). All servers are permitted to process data retrieval statements, but only some of them are permitted to make database updates. To handle this on a database-specific basis, the management application establishes a list of version tokens on each server. In the token list for a given server, token names represent database names and token values are read or write depending on whether the database must be used in read-only fashion or whether it can take reads and writes.

Client applications register a list of version tokens they require the server to match by setting a system variable. Variable setting occurs on a client-specific basis, so different clients can register different requirements. By default, the client token list is empty, which matches any server token list. When a client sets its token list to a nonempty value, matching may succeed or fail, depending on the server version token list.

To define the version token list for a server, the management application calls the version_token_set() UDF. (There are also UDFs for modifying and displaying the token list, described later.) For example, the application might send these statements to a group of three servers:

Server 1:

mysql> SELECT version_tokens_set('emp=read;prod=read');
+------------------------------------------+
| version_tokens_set('emp=read;prod=read') |
+------------------------------------------+
| 2 version tokens set.                    |
+------------------------------------------+

Server 2:

mysql> SELECT version_tokens_set('emp=write;prod=read');
+-------------------------------------------+
| version_tokens_set('emp=write;prod=read') |
+-------------------------------------------+
| 2 version tokens set.                     |
+-------------------------------------------+

Server 3:

mysql> SELECT version_tokens_set('emp=read;prod=write');
+-------------------------------------------+
| version_tokens_set('emp=read;prod=write') |
+-------------------------------------------+
| 2 version tokens set.                     |
+-------------------------------------------+

The token list in each case is specified as a semicolon-separated list of name=value pairs. The resulting token list values result in these server assingments:

  • Any server accepts reads for either database.

  • Only server 2 accepts updates for the emp database.

  • Only server 3 accepts updates for the prod database.

In addition to assigning each server a version token list, the management application also maintains a cache that reflects the server assignments.

Before communicating with the servers, a client application contacts the management application and retrieves information about server assignments. Then the client selects a server based on those assignments. Suppose that a client wants to perform both reads and writes on the emp database. Based on the preceding assignments, only server 2 qualifies. The client connects to server 2 and registers its server requirements there by setting its version_tokens_session system variable:

mysql> SET @@session.version_tokens_session = 'emp=write';

For subsequent statements sent by the client to server 2, the server compares its own version token list to the client list to check whether they match. If so, statements execute normally:

mysql> UPDATE emp.employee SET salary = salary * 1.1 WHERE id = 4981;
Query OK, 1 row affected (0.07 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> SELECT last_name, first_name FROM emp.employee WHERE id = 4981;
+-----------+------------+
| last_name | first_name |
+-----------+------------+
| Smith     | Abe        |
+-----------+------------+
1 row in set (0.01 sec)

Discrepancies between the server and client version token lists can occur two ways:

As long as the assignment of server 2 does not change, the client continues to use it for reads and writes. But suppose that the management application wants to change server assignments so that writes for the emp database must be sent to server 1 instead of server 2. To do this, it uses version_tokens_edit() to modify the emp token value on the two servers (and updates its cache of server assignments):

Server 1:

mysql> SELECT version_tokens_edit('emp=write');
+----------------------------------+
| version_tokens_edit('emp=write') |
+----------------------------------+
| 1 version tokens updated.        |
+----------------------------------+

Server 2:

mysql> SELECT version_tokens_edit('emp=read');
+---------------------------------+
| version_tokens_edit('emp=read') |
+---------------------------------+
| 1 version tokens updated.       |
+---------------------------------+

version_tokens_edit() modifies the named tokens in the server token list and leaves other tokens unchanged.

The next time the client sends a statement to server 2, its own token list no longer matches the server token list and an error occurs:

mysql> UPDATE emp.employee SET salary = salary * 1.1 WHERE id = 4982;
ERROR 3136 (42000): Version token mismatch for emp. Correct value read

In this case, the client should contact the management application to obtain updated information about server assignments, select a new server, and send the failed statement to the new server.

Note

Each client must cooperate with Version Tokens by sending only statements in accordance with the token list that it registers with a given server. For example, if a client registers a token list of 'emp=read', there is nothing in Version Tokens to prevent the client from sending updates for the emp database. The client itself must refrain from doing so.

For each statement received from a client, the server implicitly uses locking, as follows:

  • Take a shared lock for each token named in the client token list (that is, in the version_tokens_session value)

  • Perform the comparison between the server and client token lists

  • Execute the statement or produce an error depending on the comparison result

  • Release the locks

The server uses shared locks so that comparisons for multiple sessions can occur without blocking, while preventing changes to the tokens for any session that attempts to acquire an exclusive lock before it manipulates tokens of the same names in the server token list.

The preceding example uses only a few of the user-defined included in the Version Tokens plugin library, but there are others. One set of UDFs permits the server's list of version tokens to be manipulated and inspected. Another set of UDFs permits version tokens to be locked and unlocked.

These UDFs permit the server's list of version tokens to be created, changed, removed, and inspected:

  • version_tokens_set() completely replaces the current list and assigns a new list. The argument is a semicolon-separated list of name=value pairs.

  • version_tokens_edit() enables partial modifications to the current list. It can add new tokens or change the values of existing tokens. The argument is a semicolon-separated list of name=value pairs.

  • version_tokens_delete() deletes tokens from the current list. The argument is a semicolon-separated list of token names.

  • version_tokens_show() displays the current token list. It takes no argument.

Each of those functions, if successful, returns a binary string indicating what action occurred. The following example establishes the server token list, modifies it by adding a new token, deletes some tokens, and displays the resulting token list:

mysql> SELECT version_tokens_set('tok1=a;tok2=b');
+-------------------------------------+
| version_tokens_set('tok1=a;tok2=b') |
+-------------------------------------+
| 2 version tokens set.               |
+-------------------------------------+
mysql> SELECT version_tokens_edit('tok3=c');
+-------------------------------+
| version_tokens_edit('tok3=c') |
+-------------------------------+
| 1 version tokens updated.     |
+-------------------------------+
mysql> SELECT version_tokens_delete('tok2;tok1');
+------------------------------------+
| version_tokens_delete('tok2;tok1') |
+------------------------------------+
| 2 version tokens deleted.          |
+------------------------------------+
mysql> SELECT version_tokens_show();
+-----------------------+
| version_tokens_show() |
+-----------------------+
| tok3=c;               |
+-----------------------+

Warnings occur if a token list is malformed:

mysql> SELECT version_tokens_set('tok1=a; =c');
+----------------------------------+
| version_tokens_set('tok1=a; =c') |
+----------------------------------+
| 1 version tokens set.            |
+----------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> SHOW WARNINGS\G
*************************** 1. row ***************************
  Level: Warning
   Code: 42000
Message: Invalid version token pair encountered. The list provided
         is only partially updated.
1 row in set (0.00 sec)

As mentioned previously, version tokens are defined using a semicolon-separated list of name=value pairs. Consider this invocation of version_tokens_set():

mysql> SELECT version_tokens_set('tok1=b;;; tok2= a = b ; tok1 = 1\'2 3"4')
+---------------------------------------------------------------+
| version_tokens_set('tok1=b;;; tok2= a = b ; tok1 = 1\'2 3"4') |
+---------------------------------------------------------------+
| 3 version tokens set.                                         |
+---------------------------------------------------------------+

Version Tokens interprets the argument as follows:

  • Whitespace around names and values is ignored. Whitespace within names and values is permitted. (For version_tokens_delete(), which takes a list of names without values, whitespace around names is ignored.)

  • There is no quoting mechanism.

  • Order of tokens is not significant except that if a token list contains multiple instances of a given token name, the last value takes precedence over earlier values.

Given those rules, the preceding version_tokens_set() call results in a token list with two tokens: tok1 has the value 1'2 3"4, and tok2 has the value a = b. To verify this, call version_tokens_show():

mysql> SELECT version_tokens_show();
+--------------------------+
| version_tokens_show()    |
+--------------------------+
| tok2=a = b;tok1=1'2 3"4; |
+--------------------------+

If the token list contains two tokens, why did version_tokens_set() return the value 3 version tokens set? That occurred because the original token list contained two definitions for tok1, and the second definition replaced the first.

The Version Tokens token-manipulation UDFs place these constraints on token names and values:

  • Token names cannot contain = or ; characters and have a maximum length of 64 characters.

  • Token values cannot contain ; characters. Length of values is constrained by the value of the max_allowed_packet system variable.

  • Version Tokens treats token names and values as binary strings, so comparisons are case sensitive.

Version Tokens also includes a set of UDFs enabling tokens to be locked and unlocked:

  • version_tokens_lock_exclusive() acquires exclusive version token locks. It takes a list of one or more lock names and a timeout value.

  • version_tokens_lock_shared() acquires shared version token locks. It takes a list of one or more lock names and a timeout value.

  • version_tokens_unlock() releases version token locks (exclusive and shared). It takes no argument.

Each locking function returns nonzero for success. Otherwise, an error occurs:

mysql> SELECT version_tokens_lock_shared('lock1', 'lock2', 0);
+-------------------------------------------------+
| version_tokens_lock_shared('lock1', 'lock2', 0) |
+-------------------------------------------------+
|                                               1 |
+-------------------------------------------------+

mysql> SELECT version_tokens_lock_shared(NULL, 0);
ERROR 3131 (42000): Incorrect locking service lock name '(null)'.

Locking using Version Tokens locking functions is advisory; applications must agree to cooperate.

It is possible to lock nonexisting token names. This does not create the tokens.

Note

Version Tokens locking functions are based on the locking service described at Section 28.3.1, “The Locking Service”, and thus have the same semantics for shared and exclusive locks. (Version Tokens uses the locking service routines built into the server, not the locking service UDF interface, so those UDFs need not be installed to use Version Tokens.) Locks acquired by Version Tokens use a locking service namespace of version_token_locks. Locking service locks can be monitored using the Performance Schema, so this is also true for Version Tokens locks. For details, see Section 28.3.1.2.3, “Locking Service Monitoring”.

For the Version Tokens locking functions, token name arguments are used exactly as specified. Surrounding whitespace is not ignored and = and ; characters are permitted. This is because Version Tokens simply passes the token names to be locked as is to the locking service.

6.5.6.4 Version Tokens Reference

The following discussion serves as a reference to these Version Tokens components:

  • Version Tokens user-defined functions

  • Version Tokens system variables

6.5.6.4.1 Version Tokens Functions

The Version Tokens plugin library includes several user-defined functions. One set of UDFs permits the server's list of version tokens to be manipulated and inspected. Another set of UDFs permits version tokens to be locked and unlocked. The SUPER privilege is required to invoke any Version Tokens UDF.

The following UDFs permit the server's list of version tokens to be created, changed, removed, and inspected. Interpretation of name_list and token_list arguments (including whitespace handling) occurs as described in Section 6.5.6.3, “Using Version Tokens”, which provides details about the syntax for specifying tokens, as well as additional examples.

  • version_tokens_delete(name_list)

    Deletes tokens from the server's list of version tokens using the name_list argument and returns a binary string that indicates the outcome of the operation. name_list is a semicolon-separated list of version token names to delete.

    mysql> SELECT version_tokens_delete('tok1;tok3');
    +------------------------------------+
    | version_tokens_delete('tok1;tok3') |
    +------------------------------------+
    | 2 version tokens deleted.          |
    +------------------------------------+
    

    As of MySQL 5.7.9, an argument of NULL is treated as an empty string, which has no effect on the token list.

    version_tokens_delete() deletes the tokens named in its argument, if they exist. (It is not an error to delete nonexisting tokens.) To clear the token list entirely without knowing which tokens are in the list, pass NULL or a string containing no tokens to version_tokens_set():

    mysql> SELECT version_tokens_set(NULL);
    +------------------------------+
    | version_tokens_set(NULL)     |
    +------------------------------+
    | Version tokens list cleared. |
    +------------------------------+
    mysql> SELECT version_tokens_set('');
    +------------------------------+
    | version_tokens_set('')       |
    +------------------------------+
    | Version tokens list cleared. |
    +------------------------------+
    
  • version_tokens_edit(token_list)

    Modifies the server's list of version tokens using the token_list argument and returns a binary string that indicates the outcome of the operation. token_list is a semicolon-separated list of name=value pairs specifying the name of each token to be defined and its value. If a token exists, its value is updated with the given value. If a token does not exist, it is created with the given value. If the argument is NULL or a string containing no tokens, the token list remains unchanged.

    mysql> SELECT version_tokens_set('tok1=value1;tok2=value2');
    +-----------------------------------------------+
    | version_tokens_set('tok1=value1;tok2=value2') |
    +-----------------------------------------------+
    | 2 version tokens set.                         |
    +-----------------------------------------------+
    mysql> SELECT version_tokens_edit('tok2=new_value2;tok3=new_value3');
    +--------------------------------------------------------+
    | version_tokens_edit('tok2=new_value2;tok3=new_value3') |
    +--------------------------------------------------------+
    | 2 version tokens updated.                              |
    +--------------------------------------------------------+
    
  • version_tokens_set(token_list)

    Replaces the server's list of version tokens with the tokens defined in the token_list argument and returns a binary string that indicates the outcome of the operation. token_list is a semicolon-separated list of name=value pairs specifying the name of each token to be defined and its value. If the argument is NULL or a string containing no tokens, the token list is cleared.

    mysql> SELECT version_tokens_set('tok1=value1;tok2=value2');
    +-----------------------------------------------+
    | version_tokens_set('tok1=value1;tok2=value2') |
    +-----------------------------------------------+
    | 2 version tokens set.                         |
    +-----------------------------------------------+
    
  • version_tokens_show()

    Returns the server's list of version tokens as a binary string containing a semicolon-separated list of name=value pairs.

    mysql> SELECT version_tokens_show();
    +--------------------------+
    | version_tokens_show()    |
    +--------------------------+
    | tok2=value2;tok1=value1; |
    +--------------------------+
    

The following UDFs permit version tokens to be locked and unlocked:

  • version_tokens_lock_exclusive(token_name[, token_name] ..., timeout)

    Acquires exclusive locks on one or more version tokens, specified by name as strings, timing out with an error if the locks are not acquired within the given timeout value.

    mysql> SELECT version_tokens_lock_exclusive('lock1', 'lock2', 10);
    +-----------------------------------------------------+
    | version_tokens_lock_exclusive('lock1', 'lock2', 10) |
    +-----------------------------------------------------+
    |                                                   1 |
    +-----------------------------------------------------+
    

    This function was added in MySQL 5.7.8 with the name vtoken_get_write_locks() and renamed to version_tokens_lock_exclusive() in 5.7.9.

  • version_tokens_lock_shared(token_name[, token_name] ..., timeout)

    Acquires shared locks on one or more version tokens, specified by name as strings, timing out with an error if the locks are not acquired within the given timeout value.

    mysql> SELECT version_tokens_lock_shared('lock1', 'lock2', 10);
    +--------------------------------------------------+
    | version_tokens_lock_shared('lock1', 'lock2', 10) |
    +--------------------------------------------------+
    |                                                1 |
    +--------------------------------------------------+
    

    This function was added in MySQL 5.7.8 with the name vtoken_get_read_locks() and renamed to version_tokens_lock_shared() in 5.7.9.

  • version_tokens_unlock()

    Releases all locks that were acquired within the current session using version_tokens_lock_exclusive() and version_tokens_lock_shared().

    mysql> SELECT version_tokens_unlock();
    +-------------------------+
    | version_tokens_unlock() |
    +-------------------------+
    |                       1 |
    +-------------------------+
    

    This function was added in MySQL 5.7.8 with the name vtoken_release_locks() and renamed to version_tokens_unlock() in 5.7.9.

The locking functions share these characteristics:

  • The return value is nonzero for success. Otherwise, an error occurs.

  • Token names are strings.

  • In contrast to argument handling for the UDFs that manipulate the server token list, whitespace surrounding token name arguments is not ignored and = and ; characters are permitted.

  • It is possible to lock nonexisting token names. This does not create the tokens.

  • Timeout values are nonnegative integers representing the time in seconds to wait to acquire locks before timing out with an error. If the timeout is 0, there is no waiting and the function produces an error if locks cannot be acquired immediately.

  • Version Tokens locking functions are based on the locking service described at Section 28.3.1, “The Locking Service”.

6.5.6.4.2 Version Tokens System Variables

Version Tokens supports the following system variables. These variables are unavailable unless the Version Tokens plugin is installed (see Section 6.5.6.2, “Installing or Uninstalling Version Tokens”).

System variables:

  • version_tokens_session

    Introduced5.7.8
    Command-Line Format--version_tokens_session=value
    System VariableNameversion_tokens_session
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypestring
    DefaultNULL

    The session value of this variable specifies the client version token list and indicates the tokens that the client session requires the server version token list to have.

    If the version_tokens_session variable is NULL (the default) or has an empty value, any server version token list matches. (In effect, an empty value disables matching requirements.)

    If the version_tokens_session variable has a nonempty value, any mismatch between its value and the server version token list results in an error for any statement the session sends to the server. A mismatch occurs under these conditions:

    It is not a mismatch for the server version token list to include a token not named in the version_tokens_session value.

    Suppose that a management application has set the server token list as follows:

    mysql> SELECT version_tokens_set('tok1=a;tok2=b;tok3=c');
    +--------------------------------------------+
    | version_tokens_set('tok1=a;tok2=b;tok3=c') |
    +--------------------------------------------+
    | 3 version tokens set.                      |
    +--------------------------------------------+
    

    A client registers the tokens it requires the server to match by setting its version_tokens_session value. Then, for each subsequent statement sent by the client, the server checks its token list against the client version_tokens_session value and produces an error if there is a mismatch:

    mysql> SET @@session.version_tokens_session = 'tok1=a;tok2=b';
    mysql> SELECT 1;
    +---+
    | 1 |
    +---+
    | 1 |
    +---+
    
    mysql> SET @@session.version_tokens_session = 'tok1=b';
    mysql> SELECT 1;
    ERROR 3136 (42000): Version token mismatch for tok1. Correct value a
    

    The first SELECT succeeds because the client tokens tok1 and tok2 are present in the server token list and each token has the same value in the server list. The second SELECT fails because, although tok1 is present in the server token list, it has a different value than specified by the client.

    At this point, any statement sent by the client fails, unless the server token list changes such that it matches again. Suppose that the management application changes the server token list as follows:

    mysql> SELECT version_tokens_edit('tok1=b');
    +-------------------------------+
    | version_tokens_edit('tok1=b') |
    +-------------------------------+
    | 1 version tokens updated.     |
    +-------------------------------+
    mysql> SELECT version_tokens_show();
    +-----------------------+
    | version_tokens_show() |
    +-----------------------+
    | tok3=c;tok1=b;tok2=b; |
    +-----------------------+
    

    Now the client version_tokens_session value matches the server token list and the client can once again successfully execute statements:

    mysql> SELECT 1;
    +---+
    | 1 |
    +---+
    | 1 |
    +---+
    

    This variable was added in MySQL 5.7.8.

  • version_tokens_session_number

    Introduced5.7.8
    Command-Line Format--version_tokens_session_number=N
    System VariableNameversion_tokens_session_number
    Variable ScopeGlobal, Session
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default0

    This variable is for internal use.

    This variable was added in MySQL 5.7.8.

6.6 Running Multiple MySQL Instances on One Machine

In some cases, you might want to run multiple instances of MySQL on a single machine. You might want to test a new MySQL release while leaving an existing production setup undisturbed. Or you might want to give different users access to different mysqld servers that they manage themselves. (For example, you might be an Internet Service Provider that wants to provide independent MySQL installations for different customers.)

It is possible to use a different MySQL server binary per instance, or use the same binary for multiple instances, or any combination of the two approaches. For example, you might run a server from MySQL 5.6 and one from MySQL 5.7, to see how different versions handle a given workload. Or you might run multiple instances of the current production version, each managing a different set of databases.

Whether or not you use distinct server binaries, each instance that you run must be configured with unique values for several operating parameters. This eliminates the potential for conflict between instances. Parameters can be set on the command line, in option files, or by setting environment variables. See Section 5.2.3, “Specifying Program Options”. To see the values used by a given instance, connect to it and execute a SHOW VARIABLES statement.

The primary resource managed by a MySQL instance is the data directory. Each instance should use a different data directory, the location of which is specified using the --datadir=dir_name option. For methods of configuring each instance with its own data directory, and warnings about the dangers of failing to do so, see Section 6.6.1, “Setting Up Multiple Data Directories”.

In addition to using different data directories, several other options must have different values for each server instance:

  • --port=port_num

    --port controls the port number for TCP/IP connections. Alternatively, if the host has multiple network addresses, you can use --bind-address to cause each server to listen to a different address.

  • --socket={file_name|pipe_name}

    --socket controls the Unix socket file path on Unix or the named pipe name on Windows. On Windows, it is necessary to specify distinct pipe names only for those servers configured to permit named-pipe connections.

  • --shared-memory-base-name=name

    This option is used only on Windows. It designates the shared-memory name used by a Windows server to permit clients to connect using shared memory. It is necessary to specify distinct shared-memory names only for those servers configured to permit shared-memory connections.

  • --pid-file=file_name

    This option indicates the path name of the file in which the server writes its process ID.

If you use the following log file options, their values must differ for each server:

For further discussion of log file options, see Section 6.4, “MySQL Server Logs”.

To achieve better performance, you can specify the following option differently for each server, to spread the load between several physical disks:

Having different temporary directories also makes it easier to determine which MySQL server created any given temporary file.

If you have multiple MySQL installations in different locations, you can specify the base directory for each installation with the --basedir=dir_name option. This causes each instance to automatically use a different data directory, log files, and PID file because the default for each of those parameters is relative to the base directory. In that case, the only other options you need to specify are the --socket and --port options. Suppose that you install different versions of MySQL using tar file binary distributions. These install in different locations, so you can start the server for each installation using the command bin/mysqld_safe under its corresponding base directory. mysqld_safe determines the proper --basedir option to pass to mysqld, and you need specify only the --socket and --port options to mysqld_safe.

As discussed in the following sections, it is possible to start additional servers by specifying appropriate command options or by setting environment variables. However, if you need to run multiple servers on a more permanent basis, it is more convenient to use option files to specify for each server those option values that must be unique to it. The --defaults-file option is useful for this purpose.

6.6.1 Setting Up Multiple Data Directories

Each MySQL Instance on a machine should have its own data directory. The location is specified using the --datadir=dir_name option.

There are different methods of setting up a data directory for a new instance:

  • Create a new data directory.

  • Copy an existing data directory.

The following discussion provides more detail about each method.

Warning

Normally, you should never have two servers that update data in the same databases. This may lead to unpleasant surprises if your operating system does not support fault-free system locking. If (despite this warning) you run multiple servers using the same data directory and they have logging enabled, you must use the appropriate options to specify log file names that are unique to each server. Otherwise, the servers try to log to the same files.

Even when the preceding precautions are observed, this kind of setup works only with MyISAM and MERGE tables, and not with any of the other storage engines. Also, this warning against sharing a data directory among servers always applies in an NFS environment. Permitting multiple MySQL servers to access a common data directory over NFS is a very bad idea. The primary problem is that NFS is the speed bottleneck. It is not meant for such use. Another risk with NFS is that you must devise a way to ensure that two or more servers do not interfere with each other. Usually NFS file locking is handled by the lockd daemon, but at the moment there is no platform that performs locking 100% reliably in every situation.

Create a New Data Directory

With this method, the data directory will be in the same state as when you first install MySQL. It will have the default set of MySQL accounts and no user data.

On Unix, initialize the data directory. See Section 2.10, “Postinstallation Setup and Testing”.

On Windows, the data directory is included in the MySQL distribution:

  • MySQL Zip archive distributions for Windows contain an unmodified data directory. You can unpack such a distribution into a temporary location, then copy it data directory to where you are setting up the new instance.

  • Windows MSI package installers create and set up the data directory that the installed server will use, but also create a pristine template data directory named data under the installation directory. After an installation has been performed using an MSI package, the template data directory can be copied to set up additional MySQL instances.

Copy an Existing Data Directory

With this method, any MySQL accounts or user data present in the data directory are carried over to the new data directory.

  1. Stop the existing MySQL instance using the data directory. This must be a clean shutdown so that the instance flushes any pending changes to disk.

  2. Copy the data directory to the location where the new data directory should be.

  3. Copy the my.cnf or my.ini option file used by the existing instance. This serves as a basis for the new instance.

  4. Modify the new option file so that any pathnames referring to the original data directory refer to the new data directory. Also, modify any other options that must be unique per instance, such as the TCP/IP port number and the log files. For a list of parameters that must be unique per instance, see Section 6.6, “Running Multiple MySQL Instances on One Machine”.

  5. Start the new instance, telling it to use the new option file.

6.6.2 Running Multiple MySQL Instances on Windows

You can run multiple servers on Windows by starting them manually from the command line, each with appropriate operating parameters, or by installing several servers as Windows services and running them that way. General instructions for running MySQL from the command line or as a service are given in Section 2.3, “Installing MySQL on Microsoft Windows”. The following sections describe how to start each server with different values for those options that must be unique per server, such as the data directory. These options are listed in Section 6.6, “Running Multiple MySQL Instances on One Machine”.

6.6.2.1 Starting Multiple MySQL Instances at the Windows Command Line

The procedure for starting a single MySQL server manually from the command line is described in Section 2.3.5.6, “Starting MySQL from the Windows Command Line”. To start multiple servers this way, you can specify the appropriate options on the command line or in an option file. It is more convenient to place the options in an option file, but it is necessary to make sure that each server gets its own set of options. To do this, create an option file for each server and tell the server the file name with a --defaults-file option when you run it.

Suppose that you want to run one instance of mysqld on port 3307 with a data directory of C:\mydata1, and another instance on port 3308 with a data directory of C:\mydata2. Use this procedure:

  1. Make sure that each data directory exists, including its own copy of the mysql database that contains the grant tables.

  2. Create two option files. For example, create one file named C:\my-opts1.cnf that looks like this:

    [mysqld]
    datadir = C:/mydata1
    port = 3307
    

    Create a second file named C:\my-opts2.cnf that looks like this:

    [mysqld]
    datadir = C:/mydata2
    port = 3308
    
  3. Use the --defaults-file option to start each server with its own option file:

    C:\> C:\mysql\bin\mysqld --defaults-file=C:\my-opts1.cnf
    C:\> C:\mysql\bin\mysqld --defaults-file=C:\my-opts2.cnf
    

    Each server starts in the foreground (no new prompt appears until the server exits later), so you will need to issue those two commands in separate console windows.

To shut down the servers, connect to each using the appropriate port number:

C:\> C:\mysql\bin\mysqladmin --port=3307 --host=127.0.0.1 --user=root --password shutdown
C:\> C:\mysql\bin\mysqladmin --port=3308 --host=127.0.0.1 --user=root --password shutdown

Servers configured as just described permit clients to connect over TCP/IP. If your version of Windows supports named pipes and you also want to permit named-pipe connections, specify options that enable the named pipe and specify its name. Each server that supports named-pipe connections must use a unique pipe name. For example, the C:\my-opts1.cnf file might be written like this:

[mysqld]
datadir = C:/mydata1
port = 3307
enable-named-pipe
socket = mypipe1

Modify C:\my-opts2.cnf similarly for use by the second server. Then start the servers as described previously.

A similar procedure applies for servers that you want to permit shared-memory connections. Enable such connections with the --shared-memory option and specify a unique shared-memory name for each server with the --shared-memory-base-name option.

6.6.2.2 Starting Multiple MySQL Instances as Windows Services

On Windows, a MySQL server can run as a Windows service. The procedures for installing, controlling, and removing a single MySQL service are described in Section 2.3.5.8, “Starting MySQL as a Windows Service”.

To set up multiple MySQL services, you must make sure that each instance uses a different service name in addition to the other parameters that must be unique per instance.

For the following instructions, suppose that you want to run the mysqld server from two different versions of MySQL that are installed at C:\mysql-5.5.9 and C:\mysql-5.7.19, respectively. (This might be the case if you are running 5.5.9 as your production server, but also want to conduct tests using 5.7.19.)

To install MySQL as a Windows service, use the --install or --install-manual option. For information about these options, see Section 2.3.5.8, “Starting MySQL as a Windows Service”.

Based on the preceding information, you have several ways to set up multiple services. The following instructions describe some examples. Before trying any of them, shut down and remove any existing MySQL services.

  • Approach 1: Specify the options for all services in one of the standard option files. To do this, use a different service name for each server. Suppose that you want to run the 5.5.9 mysqld using the service name of mysqld1 and the 5.7.19 mysqld using the service name mysqld2. In this case, you can use the [mysqld1] group for 5.5.9 and the [mysqld2] group for 5.7.19. For example, you can set up C:\my.cnf like this:

    # options for mysqld1 service
    [mysqld1]
    basedir = C:/mysql-5.5.9
    port = 3307
    enable-named-pipe
    socket = mypipe1
    
    # options for mysqld2 service
    [mysqld2]
    basedir = C:/mysql-5.7.19
    port = 3308
    enable-named-pipe
    socket = mypipe2
    

    Install the services as follows, using the full server path names to ensure that Windows registers the correct executable program for each service:

    C:\> C:\mysql-5.5.9\bin\mysqld --install mysqld1
    C:\> C:\mysql-5.7.19\bin\mysqld --install mysqld2
    

    To start the services, use the services manager, or use NET START with the appropriate service names:

    C:\> NET START mysqld1
    C:\> NET START mysqld2
    

    To stop the services, use the services manager, or use NET STOP with the appropriate service names:

    C:\> NET STOP mysqld1
    C:\> NET STOP mysqld2
    
  • Approach 2: Specify options for each server in separate files and use --defaults-file when you install the services to tell each server what file to use. In this case, each file should list options using a [mysqld] group.

    With this approach, to specify options for the 5.5.9 mysqld, create a file C:\my-opts1.cnf that looks like this:

    [mysqld]
    basedir = C:/mysql-5.5.9
    port = 3307
    enable-named-pipe
    socket = mypipe1
    

    For the 5.7.19 mysqld, create a file C:\my-opts2.cnf that looks like this:

    [mysqld]
    basedir = C:/mysql-5.7.19
    port = 3308
    enable-named-pipe
    socket = mypipe2
    

    Install the services as follows (enter each command on a single line):

    C:\> C:\mysql-5.5.9\bin\mysqld --install mysqld1
               --defaults-file=C:\my-opts1.cnf
    C:\> C:\mysql-5.7.19\bin\mysqld --install mysqld2
               --defaults-file=C:\my-opts2.cnf
    

    When you install a MySQL server as a service and use a --defaults-file option, the service name must precede the option.

    After installing the services, start and stop them the same way as in the preceding example.

To remove multiple services, use mysqld --remove for each one, specifying a service name following the --remove option. If the service name is the default (MySQL), you can omit it.

6.6.3 Running Multiple MySQL Instances on Unix

Note

The discussion here uses mysqld_safe to launch multiple instances of MySQL. For MySQL installation using an RPM distribution, server startup and shutdown is managed by systemd on several Linux platforms. On these platforms, mysqld_safe is no longer installed because it is unnecessary. For information about using systemd to handle multiple MySQL instances, see Section 2.5.10, “Managing MySQL Server with systemd”.

One way is to run multiple MySQL instances on Unix is to compile different servers with different default TCP/IP ports and Unix socket files so that each one listens on different network interfaces. Compiling in different base directories for each installation also results automatically in a separate, compiled-in data directory, log file, and PID file location for each server.

Assume that an existing 5.6 server is configured for the default TCP/IP port number (3306) and Unix socket file (/tmp/mysql.sock). To configure a new 5.7.19 server to have different operating parameters, use a CMake command something like this:

shell> cmake . -DMYSQL_TCP_PORT=port_number \
             -DMYSQL_UNIX_ADDR=file_name \
             -DCMAKE_INSTALL_PREFIX=/usr/local/mysql-5.7.19

Here, port_number and file_name must be different from the default TCP/IP port number and Unix socket file path name, and the CMAKE_INSTALL_PREFIX value should specify an installation directory different from the one under which the existing MySQL installation is located.

If you have a MySQL server listening on a given port number, you can use the following command to find out what operating parameters it is using for several important configurable variables, including the base directory and Unix socket file name:

shell> mysqladmin --host=host_name --port=port_number variables

With the information displayed by that command, you can tell what option values not to use when configuring an additional server.

If you specify localhost as the host name, mysqladmin defaults to using a Unix socket file connection rather than TCP/IP. To explicitly specify the connection protocol, use the --protocol={TCP|SOCKET|PIPE|MEMORY} option.

You need not compile a new MySQL server just to start with a different Unix socket file and TCP/IP port number. It is also possible to use the same server binary and start each invocation of it with different parameter values at runtime. One way to do so is by using command-line options:

shell> mysqld_safe --socket=file_name --port=port_number

To start a second server, provide different --socket and --port option values, and pass a --datadir=dir_name option to mysqld_safe so that the server uses a different data directory.

Alternatively, put the options for each server in a different option file, then start each server using a --defaults-file option that specifies the path to the appropriate option file. For example, if the option files for two server instances are named /usr/local/mysql/my.cnf and /usr/local/mysql/my.cnf2, start the servers like this: command:

shell> mysqld_safe --defaults-file=/usr/local/mysql/my.cnf
shell> mysqld_safe --defaults-file=/usr/local/mysql/my.cnf2

Another way to achieve a similar effect is to use environment variables to set the Unix socket file name and TCP/IP port number:

shell> MYSQL_UNIX_PORT=/tmp/mysqld-new.sock
shell> MYSQL_TCP_PORT=3307
shell> export MYSQL_UNIX_PORT MYSQL_TCP_PORT
shell> mysql_install_db --user=mysql
shell> mysqld_safe --datadir=/path/to/datadir &

This is a quick way of starting a second server to use for testing. The nice thing about this method is that the environment variable settings apply to any client programs that you invoke from the same shell. Thus, connections for those clients are automatically directed to the second server.

Section 5.9, “MySQL Program Environment Variables”, includes a list of other environment variables you can use to affect MySQL programs.

On Unix, the mysqld_multi script provides another way to start multiple servers. See Section 5.3.4, “mysqld_multi — Manage Multiple MySQL Servers”.

6.6.4 Using Client Programs in a Multiple-Server Environment

To connect with a client program to a MySQL server that is listening to different network interfaces from those compiled into your client, you can use one of the following methods:

  • Start the client with --host=host_name --port=port_number to connect using TCP/IP to a remote server, with --host=127.0.0.1 --port=port_number to connect using TCP/IP to a local server, or with --host=localhost --socket=file_name to connect to a local server using a Unix socket file or a Windows named pipe.

  • Start the client with --protocol=TCP to connect using TCP/IP, --protocol=SOCKET to connect using a Unix socket file, --protocol=PIPE to connect using a named pipe, or --protocol=MEMORY to connect using shared memory. For TCP/IP connections, you may also need to specify --host and --port options. For the other types of connections, you may need to specify a --socket option to specify a Unix socket file or Windows named-pipe name, or a --shared-memory-base-name option to specify the shared-memory name. Shared-memory connections are supported only on Windows.

  • On Unix, set the MYSQL_UNIX_PORT and MYSQL_TCP_PORT environment variables to point to the Unix socket file and TCP/IP port number before you start your clients. If you normally use a specific socket file or port number, you can place commands to set these environment variables in your .login file so that they apply each time you log in. See Section 5.9, “MySQL Program Environment Variables”.

  • Specify the default Unix socket file and TCP/IP port number in the [client] group of an option file. For example, you can use C:\my.cnf on Windows, or the .my.cnf file in your home directory on Unix. See Section 5.2.6, “Using Option Files”.

  • In a C program, you can specify the socket file or port number arguments in the mysql_real_connect() call. You can also have the program read option files by calling mysql_options(). See Section 27.8.7, “C API Function Descriptions”.

  • If you are using the Perl DBD::mysql module, you can read options from MySQL option files. For example:

    $dsn = "DBI:mysql:test;mysql_read_default_group=client;"
            . "mysql_read_default_file=/usr/local/mysql/data/my.cnf";
    $dbh = DBI->connect($dsn, $user, $password);
    

    See Section 27.10, “MySQL Perl API”.

    Other programming interfaces may provide similar capabilities for reading option files.

6.7 Tracing mysqld Using DTrace

Support for DTrace is deprecated in MySQL 5.7 and is removed in MySQL 8.0.

The DTrace probes in the MySQL server are designed to provide information about the execution of queries within MySQL and the different areas of the system being utilized during that process. The organization and triggering of the probes means that the execution of an entire query can be monitored with one level of probes (query-start and query-done) but by monitoring other probes you can get successively more detailed information about the execution of the query in terms of the locks used, sort methods and even row-by-row and storage-engine level execution information.

The DTrace probes are organized so that you can follow the entire query process, from the point of connection from a client, through the query execution, row-level operations, and back out again. You can think of the probes as being fired within a specific sequence during a typical client connect/execute/disconnect sequence, as shown in the following figure.

Figure 6.1 The MySQL Architecture Using Pluggable Storage Engines

DTrace Probe Structure in mysqld

Global information is provided in the arguments to the DTrace probes at various levels. Global information, that is, the connection ID and user/host and where relevant the query string, is provided at key levels (connection-start, command-start, query-start, and query-exec-start). As you go deeper into the probes, it is assumed either you are only interested in the individual executions (row-level probes provide information on the database and table name only), or that you will combine the row-level probes with the notional parent probes to provide the information about a specific query. Examples of this will be given as the format and arguments of each probe are provided.

MySQL includes support for DTrace probes on these platforms:

  • Solaris 10 Update 5 (Solaris 5/08) on SPARC, x86 and x86_64 platforms

  • OS X 10.4 and higher

  • Oracle Linux 6 and higher with UEK kernel (as of MySQL 5.7.5)

Enabling the probes should be automatic on these platforms. To explicitly enable or disable the probes during building, use the -DENABLE_DTRACE=1 or -DENABLE_DTRACE=0 option to CMake.

If a non-Solaris platform includes DTrace support, building mysqld on that platform will include DTrace support.

Additional Resources

6.7.1 mysqld DTrace Probe Reference

MySQL supports the following static probes, organized into groups of functionality.

Table 6.5 MySQL DTrace Probes

GroupProbes
Connectionconnection-start, connection-done
Commandcommand-start, command-done
Queryquery-start, query-done
Query Parsingquery-parse-start, query-parse-done
Query Cachequery-cache-hit, query-cache-miss
Query Executionquery-exec-start, query-exec-done
Row Levelinsert-row-start, insert-row-done
 update-row-start, update-row-done
 delete-row-start, delete-row-done
Row Readsread-row-start, read-row-done
Index Readsindex-read-row-start, index-read-row-done
Lockhandler-rdlock-start, handler-rdlock-done
 handler-wrlock-start, handler-wrlock-done
 handler-unlock-start, handler-unlock-done
Filesortfilesort-start, filesort-done
Statementselect-start, select-done
 insert-start, insert-done
 insert-select-start, insert-select-done
 update-start, update-done
 multi-update-start, multi-update-done
 delete-start, delete-done
 multi-delete-start, multi-delete-done
Networknet-read-start, net-read-done, net-write-start, net-write-done
Keycachekeycache-read-start, keycache-read-block, keycache-read-done, keycache-read-hit, keycache-read-miss, keycache-write-start, keycache-write-block, keycache-write-done

Note

When extracting the argument data from the probes, each argument is available as argN, starting with arg0. To identify each argument within the definitions they are provided with a descriptive name, but you must access the information using the corresponding argN parameter.

6.7.1.1 Connection Probes

The connection-start and connection-done probes enclose a connection from a client, regardless of whether the connection is through a socket or network connection.

connection-start(connectionid, user, host)
connection-done(status, connectionid)
  • connection-start: Triggered after a connection and successful login/authentication have been completed by a client. The arguments contain the connection information:

    • connectionid: An unsigned long containing the connection ID. This is the same as the process ID shown as the Id value in the output from SHOW PROCESSLIST.

    • user: The username used when authenticating. The value will be blank for the anonymous user.

    • host: The host of the client connection. For a connection made using Unix sockets, the value will be blank.

  • connection-done: Triggered just as the connection to the client has been closed. The arguments are:

    • status: The status of the connection when it was closed. A logout operation will have a value of 0; any other termination of the connection has a nonzero value.

    • connectionid: The connection ID of the connection that was closed.

The following D script will quantify and summarize the average duration of individual connections, and provide a count, dumping the information every 60 seconds:

#!/usr/sbin/dtrace -s


mysql*:::connection-start
{
  self->start = timestamp;
}

mysql*:::connection-done
/self->start/
{
  @ = quantize(((timestamp - self->start)/1000000));
  self->start = 0;
}

tick-60s
{
  printa(@);
}

When executed on a server with a large number of clients you might see output similar to this:

  1  57413                        :tick-60s

           value  ------------- Distribution ------------- count
              -1 |                                         0
               0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 30011
               1 |                                         59
               2 |                                         5
               4 |                                         20
               8 |                                         29
              16 |                                         18
              32 |                                         27
              64 |                                         30
             128 |                                         11
             256 |                                         10
             512 |                                         1
            1024 |                                         6
            2048 |                                         8
            4096 |                                         9
            8192 |                                         8
           16384 |                                         2
           32768 |                                         1
           65536 |                                         1
          131072 |                                         0
          262144 |                                         1
524288 |                                         0        

6.7.1.2 Command Probes

The command probes are executed before and after a client command is executed, including any SQL statement that might be executed during that period. Commands include operations such as the initialization of the DB, use of the COM_CHANGE_USER operation (supported by the MySQL protocol), and manipulation of prepared statements. Many of these commands are used only by the MySQL client API from various connectors such as PHP and Java.

command-start(connectionid, command, user, host)
command-done(status)
  • command-start: Triggered when a command is submitted to the server.

    • connectionid: The connection ID of the client executing the command.

    • command: An integer representing the command that was executed. Possible values are shown in the following table.

      ValueNameDescription
      00COM_SLEEPInternal thread state
      01COM_QUITClose connection
      02COM_INIT_DBSelect database (USE ...)
      03COM_QUERYExecute a query
      04COM_FIELD_LISTGet a list of fields
      05COM_CREATE_DBCreate a database (deprecated)
      06COM_DROP_DBDrop a database (deprecated)
      07COM_REFRESHRefresh connection
      08COM_SHUTDOWNShutdown server
      09COM_STATISTICSGet statistics
      10COM_PROCESS_INFOGet processes (SHOW PROCESSLIST)
      11COM_CONNECTInitialize connection
      12COM_PROCESS_KILLKill process
      13COM_DEBUGGet debug information
      14COM_PINGPing
      15COM_TIMEInternal thread state
      16COM_DELAYED_INSERTInternal thread state
      17COM_CHANGE_USERChange user
      18COM_BINLOG_DUMPUsed by a replication slave or mysqlbinlog to initiate a binary log read
      19COM_TABLE_DUMPUsed by a replication slave to get the master table information
      20COM_CONNECT_OUTUsed by a replication slave to log a connection to the server
      21COM_REGISTER_SLAVEUsed by a replication slave during registration
      22COM_STMT_PREPAREPrepare a statement
      23COM_STMT_EXECUTEExecute a statement
      24COM_STMT_SEND_LONG_DATAUsed by a client when requesting extended data
      25COM_STMT_CLOSEClose a prepared statement
      26COM_STMT_RESETReset a prepared statement
      27COM_SET_OPTIONSet a server option
      28COM_STMT_FETCHFetch a prepared statement
    • user: The user executing the command.

    • host: The client host.

  • command-done: Triggered when the command execution completes. The status argument contains 0 if the command executed successfully, or 1 if the statement was terminated before normal completion.

The command-start and command-done probes are best used when combined with the statement probes to get an idea of overall execution time.

6.7.1.3 Query Probes

The query-start and query-done probes are triggered when a specific query is received by the server and when the query has been completed and the information has been successfully sent to the client.

query-start(query, connectionid, database, user, host)
query-done(status)
  • query-start: Triggered after the query string has been received from the client. The arguments are:

    • query: The full text of the submitted query.

    • connectionid: The connection ID of the client that submitted the query. The connection ID equals the connection ID returned when the client first connects and the Id value in the output from SHOW PROCESSLIST.

    • database: The database name on which the query is being executed.

    • user: The username used to connect to the server.

    • host: The hostname of the client.

  • query-done: Triggered once the query has been executed and the information has been returned to the client. The probe includes a single argument, status, which returns 0 when the query is successfully executed and 1 if there was an error.

You can get a simple report of the execution time for each query using the following D script:

#!/usr/sbin/dtrace -s

#pragma D option quiet

dtrace:::BEGIN
{
   printf("%-20s %-20s %-40s %-9s\n", "Who", "Database", "Query", "Time(ms)");
}

mysql*:::query-start
{
   self->query = copyinstr(arg0);
   self->connid = arg1;
   self->db    = copyinstr(arg2);
   self->who   = strjoin(copyinstr(arg3),strjoin("@",copyinstr(arg4)));
   self->querystart = timestamp;
}

mysql*:::query-done
{
   printf("%-20s %-20s %-40s %-9d\n",self->who,self->db,self->query,
          (timestamp - self->querystart) / 1000000);
}

When executing the above script you should get a basic idea of the execution time of your queries:

shell> ./query.d
Who                  Database             Query                                    Time(ms)
root@localhost       test                 select * from t1 order by i limit 10     0
root@localhost       test                 set global query_cache_size=0            0
root@localhost       test                 select * from t1 order by i limit 10     776
root@localhost       test                 select * from t1 order by i limit 10     773
root@localhost       test                 select * from t1 order by i desc limit 10 795 

6.7.1.4 Query Parsing Probes

The query parsing probes are triggered before the original SQL statement is parsed and when the parsing of the statement and determination of the execution model required to process the statement has been completed:

query-parse-start(query)
query-parse-done(status)
  • query-parse-start: Triggered just before the statement is parsed by the MySQL query parser. The single argument, query, is a string containing the full text of the original query.

  • query-parse-done: Triggered when the parsing of the original statement has been completed. The status is an integer describing the status of the operation. A 0 indicates that the query was successfully parsed. A 1 indicates that the parsing of the query failed.

For example, you could monitor the execution time for parsing a given query using the following D script:

#!/usr/sbin/dtrace -s

#pragma D option quiet

mysql*:::query-parse-start
{
   self->parsestart = timestamp;
   self->parsequery = copyinstr(arg0);
}

mysql*:::query-parse-done
/arg0 == 0/
{
   printf("Parsing %s: %d microseconds\n", self->parsequery,((timestamp - self->parsestart)/1000));
}

mysql*:::query-parse-done
/arg0 != 0/
{
   printf("Error parsing %s: %d microseconds\n", self->parsequery,((timestamp - self->parsestart)/1000));
}

In the above script a predicate is used on query-parse-done so that different output is generated based on the status value of the probe.

When running the script and monitoring the execution:

shell> ./query-parsing.d
Error parsing select from t1 join (t2) on (t1.i = t2.i) order by t1.s,t1.i limit 10: 36 ms
Parsing select * from t1 join (t2) on (t1.i = t2.i) order by t1.s,t1.i limit 10: 176 ms

6.7.1.5 Query Cache Probes

The query cache probes are fired when executing any query. The query-cache-hit query is triggered when a query exists in the query cache and can be used to return the query cache information. The arguments contain the original query text and the number of rows returned from the query cache for the query. If the query is not within the query cache, or the query cache is not enabled, then the query-cache-miss probe is triggered instead.

query-cache-hit(query, rows)
query-cache-miss(query)
  • query-cache-hit: Triggered when the query has been found within the query cache. The first argument, query, contains the original text of the query. The second argument, rows, is an integer containing the number of rows in the cached query.

  • query-cache-miss: Triggered when the query is not found within the query cache. The first argument, query, contains the original text of the query.

The query cache probes are best combined with a probe on the main query so that you can determine the differences in times between using or not using the query cache for specified queries. For example, in the following D script, the query and query cache information are combined into the information output during monitoring:

#!/usr/sbin/dtrace -s

#pragma D option quiet

dtrace:::BEGIN
{
   printf("%-20s %-20s %-40s %2s %-9s\n", "Who", "Database", "Query", "QC", "Time(ms)");
}

mysql*:::query-start
{
   self->query = copyinstr(arg0);
   self->connid = arg1;
   self->db    = copyinstr(arg2);
   self->who   = strjoin(copyinstr(arg3),strjoin("@",copyinstr(arg4)));
   self->querystart = timestamp;
   self->qc = 0;
}

mysql*:::query-cache-hit
{
   self->qc = 1;
}

mysql*:::query-cache-miss
{
   self->qc = 0;
}

mysql*:::query-done
{
   printf("%-20s %-20s %-40s %-2s %-9d\n",self->who,self->db,self->query,(self->qc ? "Y" : "N"),
          (timestamp - self->querystart) / 1000000);
}

When executing the script you can see the effects of the query cache. Initially the query cache is disabled. If you set the query cache size and then execute the query multiple times you should see that the query cache is being used to return the query data:

shell> ./query-cache.d
root@localhost       test                 select * from t1 order by i limit 10     N  1072
root@localhost                            set global query_cache_size=262144       N  0
root@localhost       test                 select * from t1 order by i limit 10     N  781
root@localhost       test                 select * from t1 order by i limit 10     Y  0 

6.7.1.6 Query Execution Probes

The query execution probe is triggered when the actual execution of the query starts, after the parsing and checking the query cache but before any privilege checks or optimization. By comparing the difference between the start and done probes you can monitor the time actually spent servicing the query (instead of just handling the parsing and other elements of the query).

query-exec-start(query, connectionid, database, user, host, exec_type)
query-exec-done(status)
Note

The information provided in the arguments for query-start and query-exec-start are almost identical and designed so that you can choose to monitor either the entire query process (using query-start) or only the execution (using query-exec-start) while exposing the core information about the user, client, and query being executed.

  • query-exec-start: Triggered when the execution of a individual query is started. The arguments are:

    • query: The full text of the submitted query.

    • connectionid: The connection ID of the client that submitted the query. The connection ID equals the connection ID returned when the client first connects and the Id value in the output from SHOW PROCESSLIST.

    • database: The database name on which the query is being executed.

    • user: The username used to connect to the server.

    • host: The hostname of the client.

    • exec_type: The type of execution. Execution types are determined based on the contents of the query and where it was submitted. The values for each type are shown in the following table.

      ValueDescription
      0Executed query from sql_parse, top-level query.
      1Executed prepared statement
      2Executed cursor statement
      3Executed query in stored procedure
  • query-exec-done: Triggered when the execution of the query has completed. The probe includes a single argument, status, which returns 0 when the query is successfully executed and 1 if there was an error.

6.7.1.7 Row-Level Probes

The *row-{start,done} probes are triggered each time a row operation is pushed down to a storage engine. For example, if you execute an INSERT statement with 100 rows of data, then the insert-row-start and insert-row-done probes will be triggered 100 times each, for each row insert.

insert-row-start(database, table)
insert-row-done(status)

update-row-start(database, table)
update-row-done(status)

delete-row-start(database, table)
delete-row-done(status)
  • insert-row-start: Triggered before a row is inserted into a table.

  • insert-row-done: Triggered after a row is inserted into a table.

  • update-row-start: Triggered before a row is updated in a table.

  • update-row-done: Triggered before a row is updated in a table.

  • delete-row-start: Triggered before a row is deleted from a table.

  • delete-row-done: Triggered before a row is deleted from a table.

The arguments supported by the probes are consistent for the corresponding start and done probes in each case:

  • database: The database name.

  • table: The table name.

  • status: The status; 0 for success or 1 for failure.

Because the row-level probes are triggered for each individual row access, these probes can be triggered many thousands of times each second, which may have a detrimental effect on both the monitoring script and MySQL. The DTrace environment should limit the triggering on these probes to prevent the performance being adversely affected. Either use the probes sparingly, or use counter or aggregation functions to report on these probes and then provide a summary when the script terminates or as part of a query-done or query-exec-done probes.

The following example script summarizes the duration of each row operation within a larger query:

#!/usr/sbin/dtrace -s

#pragma D option quiet

dtrace:::BEGIN
{
   printf("%-2s %-10s %-10s %9s %9s %-s \n",
          "St", "Who", "DB", "ConnID", "Dur ms", "Query");
}

mysql*:::query-start
{
   self->query = copyinstr(arg0);
   self->who   = strjoin(copyinstr(arg3),strjoin("@",copyinstr(arg4)));
   self->db    = copyinstr(arg2);
   self->connid = arg1;
   self->querystart = timestamp;
   self->rowdur = 0;
}

mysql*:::query-done
{
   this->elapsed = (timestamp - self->querystart) /1000000;
   printf("%2d %-10s %-10s %9d %9d %s\n",
          arg0, self->who, self->db,
          self->connid, this->elapsed, self->query);
}

mysql*:::query-done
/ self->rowdur /
{
   printf("%34s %9d %s\n", "", (self->rowdur/1000000), "-> Row ops");
}

mysql*:::insert-row-start
{
   self->rowstart = timestamp;
}

mysql*:::delete-row-start
{
   self->rowstart = timestamp;
}

mysql*:::update-row-start
{
   self->rowstart = timestamp;
}

mysql*:::insert-row-done
{
   self->rowdur += (timestamp-self->rowstart);
}

mysql*:::delete-row-done
{
   self->rowdur += (timestamp-self->rowstart);
}

mysql*:::update-row-done
{
   self->rowdur += (timestamp-self->rowstart);
}

Running the above script with a query that inserts data into a table, you can monitor the exact time spent performing the raw row insertion:

St Who        DB            ConnID    Dur ms Query
 0 @localhost test              13     20767 insert into t1(select * from t2)
                                        4827 -> Row ops

6.7.1.8 Read Row Probes

The read row probes are triggered at a storage engine level each time a row read operation occurs. These probes are specified within each storage engine (as opposed to the *row-start probes which are in the storage engine interface). These probes can therefore be used to monitor individual storage engine row-level operations and performance. Because these probes are triggered around the storage engine row read interface, they may be hit a significant number of times during a basic query.

read-row-start(database, table, scan_flag)
read-row-done(status)
  • read-row-start: Triggered when a row is read by the storage engine from the specified database and table. The scan_flag is set to 1 (true) when the read is part of a table scan (that is, a sequential read), or 0 (false) when the read is of a specific record.

  • read-row-done: Triggered when a row read operation within a storage engine completes. The status returns 0 on success, or a positive value on failure.

6.7.1.9 Index Probes

The index probes are triggered each time a row is read using one of the indexes for the specified table. The probe is triggered within the corresponding storage engine for the table.

index-read-row-start(database, table)
index-read-row-done(status)
  • index-read-row-start: Triggered when a row is read by the storage engine from the specified database and table.

  • index-read-row-done: Triggered when an indexed row read operation within a storage engine completes. The status returns 0 on success, or a positive value on failure.

6.7.1.10 Lock Probes

The lock probes are called whenever an external lock is requested by MySQL for a table using the corresponding lock mechanism on the table as defined by the table's engine type. There are three different types of lock, the read lock, write lock, and unlock operations. Using the probes you can determine the duration of the external locking routine (that is, the time taken by the storage engine to implement the lock, including any time waiting for another lock to become free) and the total duration of the lock/unlock process.

handler-rdlock-start(database, table)
handler-rdlock-done(status)

handler-wrlock-start(database, table)
handler-wrlock-done(status)

handler-unlock-start(database, table)
handler-unlock-done(status)
  • handler-rdlock-start: Triggered when a read lock is requested on the specified database and table.

  • handler-wrlock-start: Triggered when a write lock is requested on the specified database and table.

  • handler-unlock-start: Triggered when an unlock request is made on the specified database and table.

  • handler-rdlock-done: Triggered when a read lock request completes. The status is 0 if the lock operation succeeded, or >0 on failure.

  • handler-wrlock-done: Triggered when a write lock request completes. The status is 0 if the lock operation succeeded, or >0 on failure.

  • handler-unlock-done: Triggered when an unlock request completes. The status is 0 if the unlock operation succeeded, or >0 on failure.

You can use arrays to monitor the locking and unlocking of individual tables and then calculate the duration of the entire table lock using the following script:

#!/usr/sbin/dtrace -s

#pragma D option quiet

mysql*:::handler-rdlock-start
{
   self->rdlockstart = timestamp;
   this->lockref = strjoin(copyinstr(arg0),strjoin("@",copyinstr(arg1)));
   self->lockmap[this->lockref] = self->rdlockstart;
   printf("Start: Lock->Read   %s.%s\n",copyinstr(arg0),copyinstr(arg1));
}

mysql*:::handler-wrlock-start
{
   self->wrlockstart = timestamp;
   this->lockref = strjoin(copyinstr(arg0),strjoin("@",copyinstr(arg1)));
   self->lockmap[this->lockref] = self->rdlockstart;
   printf("Start: Lock->Write  %s.%s\n",copyinstr(arg0),copyinstr(arg1));
}

mysql*:::handler-unlock-start
{
   self->unlockstart = timestamp;
   this->lockref = strjoin(copyinstr(arg0),strjoin("@",copyinstr(arg1)));
   printf("Start: Lock->Unlock %s.%s (%d ms lock duration)\n",
          copyinstr(arg0),copyinstr(arg1),
          (timestamp - self->lockmap[this->lockref])/1000000);
}

mysql*:::handler-rdlock-done
{
   printf("End:   Lock->Read   %d ms\n",
          (timestamp - self->rdlockstart)/1000000);
}

mysql*:::handler-wrlock-done
{
   printf("End:   Lock->Write  %d ms\n",
          (timestamp - self->wrlockstart)/1000000);
}

mysql*:::handler-unlock-done
{
   printf("End:   Lock->Unlock %d ms\n",
          (timestamp - self->unlockstart)/1000000);
}

When executed, you should get information both about the duration of the locking process itself, and of the locks on a specific table:

Start: Lock->Read   test.t2
End:   Lock->Read   0 ms
Start: Lock->Unlock test.t2 (25743 ms lock duration)
End:   Lock->Unlock 0 ms
Start: Lock->Read   test.t2
End:   Lock->Read   0 ms
Start: Lock->Unlock test.t2 (1 ms lock duration)
End:   Lock->Unlock 0 ms
Start: Lock->Read   test.t2
End:   Lock->Read   0 ms
Start: Lock->Unlock test.t2 (1 ms lock duration)
End:   Lock->Unlock 0 ms
Start: Lock->Read   test.t2
End:   Lock->Read   0 ms

6.7.1.11 Filesort Probes

The filesort probes are triggered whenever a filesort operation is applied to a table. For more information on filesort and the conditions under which it occurs, see Section 9.2.1.13, “ORDER BY Optimization”.

filesort-start(database, table)
filesort-done(status, rows)
  • filesort-start: Triggered when the filesort operation starts on a table. The two arguments to the probe, database and table, will identify the table being sorted.

  • filesort-done: Triggered when the filesort operation completes. Two arguments are supplied, the status (0 for success, 1 for failure), and the number of rows sorted during the filesort process.

An example of this is in the following script, which tracks the duration of the filesort process in addition to the duration of the main query:

#!/usr/sbin/dtrace -s

#pragma D option quiet

dtrace:::BEGIN
{
   printf("%-2s %-10s %-10s %9s %18s %-s \n",
          "St", "Who", "DB", "ConnID", "Dur microsec", "Query");
}

mysql*:::query-start
{
   self->query = copyinstr(arg0);
   self->who   = strjoin(copyinstr(arg3),strjoin("@",copyinstr(arg4)));
   self->db    = copyinstr(arg2);
   self->connid = arg1;
   self->querystart = timestamp;
   self->filesort = 0;
   self->fsdb = "";
   self->fstable = "";
}

mysql*:::filesort-start
{
  self->filesort = timestamp;
  self->fsdb = copyinstr(arg0);
  self->fstable = copyinstr(arg1);
}

mysql*:::filesort-done
{
   this->elapsed = (timestamp - self->filesort) /1000;
   printf("%2d %-10s %-10s %9d %18d Filesort on %s\n",
          arg0, self->who, self->fsdb,
          self->connid, this->elapsed, self->fstable);
}

mysql*:::query-done
{
   this->elapsed = (timestamp - self->querystart) /1000;
   printf("%2d %-10s %-10s %9d %18d %s\n",
          arg0, self->who, self->db,
          self->connid, this->elapsed, self->query);
}

Executing a query on a large table with an ORDER BY clause that triggers a filesort, and then creating an index on the table and then repeating the same query, you can see the difference in execution speed:

St Who        DB            ConnID       Dur microsec Query
 0 @localhost test              14           11335469 Filesort on t1
 0 @localhost test              14           11335787 select * from t1 order by i limit 100
 0 @localhost test              14          466734378 create index t1a on t1 (i)
 0 @localhost test              14              26472 select * from t1 order by i limit 100

6.7.1.12 Statement Probes

The individual statement probes are provided to give specific information about different statement types. For the start probes the string of the query is provided as the only argument. Depending on the statement type, the information provided by the corresponding done probe will differ. For all done probes the status of the operation (0 for success, >0 for failure) is provided. For SELECT, INSERT, INSERT ... (SELECT FROM ...), DELETE, and DELETE FROM t1,t2 operations the number of rows affected is returned.

For UPDATE and UPDATE t1,t2 ... statements the number of rows matched and the number of rows actually changed is provided. This is because the number of rows actually matched by the corresponding WHERE clause, and the number of rows changed can differ. MySQL does not update the value of a row if the value already matches the new setting.

select-start(query)
select-done(status,rows)

insert-start(query)
insert-done(status,rows)

insert-select-start(query)
insert-select-done(status,rows)

update-start(query)
update-done(status,rowsmatched,rowschanged)

multi-update-start(query)
multi-update-done(status,rowsmatched,rowschanged)

delete-start(query)
delete-done(status,rows)

multi-delete-start(query)
multi-delete-done(status,rows)
  • select-start: Triggered before a SELECT statement.

  • select-done: Triggered at the end of a SELECT statement.

  • insert-start: Triggered before a INSERT statement.

  • insert-done: Triggered at the end of an INSERT statement.

  • insert-select-start: Triggered before an INSERT ... SELECT statement.

  • insert-select-done: Triggered at the end of an INSERT ... SELECT statement.

  • update-start: Triggered before an UPDATE statement.

  • update-done: Triggered at the end of an UPDATE statement.

  • multi-update-start: Triggered before an UPDATE statement involving multiple tables.

  • multi-update-done: Triggered at the end of an UPDATE statement involving multiple tables.

  • delete-start: Triggered before a DELETE statement.

  • delete-done: Triggered at the end of a DELETE statement.

  • multi-delete-start: Triggered before a DELETE statement involving multiple tables.

  • multi-delete-done: Triggered at the end of a DELETE statement involving multiple tables.

The arguments for the statement probes are:

  • query: The query string.

  • status: The status of the query. 0 for success, and >0 for failure.

  • rows: The number of rows affected by the statement. This returns the number rows found for SELECT, the number of rows deleted for DELETE, and the number of rows successfully inserted for INSERT.

  • rowsmatched: The number of rows matched by the WHERE clause of an UPDATE operation.

  • rowschanged: The number of rows actually changed during an UPDATE operation.

You use these probes to monitor the execution of these statement types without having to monitor the user or client executing the statements. A simple example of this is to track the execution times:

#!/usr/sbin/dtrace -s

#pragma D option quiet

dtrace:::BEGIN
{
   printf("%-60s %-8s %-8s %-8s\n", "Query", "RowsU", "RowsM", "Dur (ms)");
}

mysql*:::update-start, mysql*:::insert-start,
mysql*:::delete-start, mysql*:::multi-delete-start,
mysql*:::multi-delete-done, mysql*:::select-start,
mysql*:::insert-select-start, mysql*:::multi-update-start
{
    self->query = copyinstr(arg0);
    self->querystart = timestamp;
}

mysql*:::insert-done, mysql*:::select-done,
mysql*:::delete-done, mysql*:::multi-delete-done, mysql*:::insert-select-done
/ self->querystart /
{
    this->elapsed = ((timestamp - self->querystart)/1000000);
    printf("%-60s %-8d %-8d %d\n",
           self->query,
           0,
           arg1,
           this->elapsed);
    self->querystart = 0;
}

mysql*:::update-done, mysql*:::multi-update-done
/ self->querystart /
{
    this->elapsed = ((timestamp - self->querystart)/1000000);
    printf("%-60s %-8d %-8d %d\n",
           self->query,
           arg1,
           arg2,
           this->elapsed);
    self->querystart = 0;
}

When executed you can see the basic execution times and rows matches:

Query                                                        RowsU    RowsM    Dur (ms)
select * from t2                                             0        275      0
insert into t2 (select * from t2)                            0        275      9
update t2 set i=5 where i > 75                               110      110      8
update t2 set i=5 where i < 25                               254      134      12
delete from t2 where i < 5                                   0        0        0

Another alternative is to use the aggregation functions in DTrace to aggregate the execution time of individual statements together:

#!/usr/sbin/dtrace -s

#pragma D option quiet


mysql*:::update-start, mysql*:::insert-start,
mysql*:::delete-start, mysql*:::multi-delete-start,
mysql*:::multi-delete-done, mysql*:::select-start,
mysql*:::insert-select-start, mysql*:::multi-update-start
{
    self->querystart = timestamp;
}

mysql*:::select-done
{
        @statements["select"] = sum(((timestamp - self->querystart)/1000000));
}

mysql*:::insert-done, mysql*:::insert-select-done
{
        @statements["insert"] = sum(((timestamp - self->querystart)/1000000));
}

mysql*:::update-done, mysql*:::multi-update-done
{
        @statements["update"] = sum(((timestamp - self->querystart)/1000000));
}

mysql*:::delete-done, mysql*:::multi-delete-done
{
        @statements["delete"] = sum(((timestamp - self->querystart)/1000000));
}

tick-30s
{
        printa(@statements);
}

The script just shown aggregates the times spent doing each operation, which could be used to help benchmark a standard suite of tests.

 delete                                                            0
  update                                                            0
  insert                                                           23
  select                                                         2484

  delete                                                            0
  update                                                            0
  insert                                                           39
  select                                                        10744

  delete                                                            0
  update                                                           26
  insert                                                           56
  select                                                        10944

  delete                                                            0
  update                                                           26
  insert                                                         2287
  select                                                        15985

6.7.1.13 Network Probes

The network probes monitor the transfer of information from the MySQL server and clients of all types over the network. The probes are defined as follows:

net-read-start()
net-read-done(status, bytes)
net-write-start(bytes)
net-write-done(status)
  • net-read-start: Triggered when a network read operation is started.

  • net-read-done: Triggered when the network read operation completes. The status is an integer representing the return status for the operation, 0 for success and 1 for failure. The bytes argument is an integer specifying the number of bytes read during the process.

  • net-start-bytes: Triggered when data is written to a network socket. The single argument, bytes, specifies the number of bytes written to the network socket.

  • net-write-done: Triggered when the network write operation has completed. The single argument, status, is an integer representing the return status for the operation, 0 for success and 1 for failure.

You can use the network probes to monitor the time spent reading from and writing to network clients during execution. The following D script provides an example of this. Both the cumulative time for the read or write is calculated, and the number of bytes. Note that the dynamic variable size has been increased (using the dynvarsize option) to cope with the rapid firing of the individual probes for the network reads/writes.

#!/usr/sbin/dtrace -s

#pragma D option quiet
#pragma D option dynvarsize=4m

dtrace:::BEGIN
{
   printf("%-2s %-30s %-10s %9s %18s %-s \n",
          "St", "Who", "DB", "ConnID", "Dur microsec", "Query");
}

mysql*:::query-start
{
   self->query = copyinstr(arg0);
   self->who   = strjoin(copyinstr(arg3),strjoin("@",copyinstr(arg4)));
   self->db    = copyinstr(arg2);
   self->connid = arg1;
   self->querystart = timestamp;
   self->netwrite = 0;
   self->netwritecum = 0;
   self->netwritebase = 0;
   self->netread = 0;
   self->netreadcum = 0;
   self->netreadbase = 0;
}

mysql*:::net-write-start
{
   self->netwrite += arg0;
   self->netwritebase = timestamp;
}

mysql*:::net-write-done
{
   self->netwritecum += (timestamp - self->netwritebase);
   self->netwritebase = 0;
}

mysql*:::net-read-start
{
   self->netreadbase = timestamp;
}

mysql*:::net-read-done
{
   self->netread += arg1;
   self->netreadcum += (timestamp - self->netreadbase);
   self->netreadbase = 0;
}

mysql*:::query-done
{
   this->elapsed = (timestamp - self->querystart) /1000000;
   printf("%2d %-30s %-10s %9d %18d %s\n",
          arg0, self->who, self->db,
          self->connid, this->elapsed, self->query);
   printf("Net read: %d bytes (%d ms) write: %d bytes (%d ms)\n",
               self->netread, (self->netreadcum/1000000),
               self->netwrite, (self->netwritecum/1000000));
}

When executing the above script on a machine with a remote client, you can see that approximately a third of the time spent executing the query is related to writing the query results back to the client.

St Who                            DB            ConnID       Dur microsec Query
 0 root@::ffff:192.168.0.108      test              31               3495 select * from t1 limit 1000000
Net read: 0 bytes (0 ms) write: 10000075 bytes (1220 ms)

6.7.1.14 Keycache Probes

The keycache probes are triggered when using the index key cache used with the MyISAM storage engine. Probes exist to monitor when data is read into the keycache, cached key data is written from the cache into a cached file, or when accessing the keycache.

Keycache usage indicates when data is read or written from the index files into the cache, and can be used to monitor how efficient the memory allocated to the keycache is being used. A high number of keycache reads across a range of queries may indicate that the keycache is too small for size of data being accessed.

keycache-read-start(filepath, bytes, mem_used, mem_free)
keycache-read-block(bytes)
keycache-read-hit()
keycache-read-miss()
keycache-read-done(mem_used, mem_free)
keycache-write-start(filepath, bytes, mem_used, mem_free)
keycache-write-block(bytes)
keycache-write-done(mem_used, mem_free)

When reading data from the index files into the keycache, the process first initializes the read operation (indicated by keycache-read-start), then loads blocks of data (keycache-read-block), and then the read block is either matches the data being identified (keycache-read-hit) or more data needs to be read (keycache-read-miss). Once the read operation has completed, reading stops with the keycache-read-done.

Data will be read from the index file into the keycache only when the specified key is not already within the keycache.

  • keycache-read-start: Triggered when the keycache read operation is started. Data is read from the specified filepath, reading the specified number of bytes. The mem_used and mem_avail indicate memory currently used by the keycache and the amount of memory available within the keycache.

  • keycache-read-block: Triggered when the keycache reads a block of data, of the specified number of bytes, from the index file into the keycache.

  • keycache-read-hit: Triggered when the block of data read from the index file matches the key data requested.

  • keycache-read-miss: Triggered when the block of data read from the index file does not match the key data needed.

  • keycache-read-done: Triggered when the keycache read operation has completed. The mem_used and mem_avail indicate memory currently used by the keycache and the amount of memory available within the keycache.

Keycache writes occur when the index information is updated during an INSERT, UPDATE, or DELETE operation, and the cached key information is flushed back to the index file.

  • keycache-write-start: Triggered when the keycache write operation is started. Data is written to the specified filepath, reading the specified number of bytes. The mem_used and mem_avail indicate memory currently used by the keycache and the amount of memory available within the keycache.

  • keycache-write-block: Triggered when the keycache writes a block of data, of the specified number of bytes, to the index file from the keycache.

  • keycache-write-done: Triggered when the keycache write operation has completed. The mem_used and mem_avail indicate memory currently used by the keycache and the amount of memory available within the keycache.