10 Database Administration with SQL*Plus

This chapter provides a brief overview of the database administration tools available in SQL*Plus, and discusses the following topics:

Overview
Introduction to Database Startup and Shutdown
Redo Log Files
Database Recovery

This chapter is intended for use by database administrators. You must have database administrator privileges to use this functionality.

For more information on database administration, see the Oracle Database Concepts manual.

Overview

Special operations such as starting up or shutting down a database are performed by a database administrator (DBA). The DBA has certain privileges that are not assigned to normal users. The commands outlined in this chapter would normally be used by a DBA.

For more information about security and roles in SQL*Plus, see SQL*Plus Security.

Introduction to Database Startup and Shutdown

An Oracle database may not always be available to all users. To open or close a database, or to start up or shut down an instance, you must have DBA privileges or be connected as SYSOPER or SYSDBA. Other users cannot change the current status of an Oracle database.

Database Startup

Starting a database involves three steps:

Starting an instance

An instance controls the background processes and the allocation of memory area to access an Oracle database.
Mounting the database

Mounting the database associates it with a previously started instance.
Opening the database

Opening the database makes it available for normal database operations.

For more information about database startup, see the Oracle Database Concepts guide. For more information about starting a database, see the STARTUP command.

Example 10-1 Starting an Instance

To start an Oracle Database instance, without mounting the database, enter

STARTUP NOMOUNT

Example 10-2 Mounting the Database

To start an instance, mount the database, but leave the database closed, enter

STARTUP MOUNT

Example 10-3 Opening the Database

To start an instance using the Oracle Database Server parameter file INITSALES.ORA, mount and open the database named SALES, and restrict access to database administrators, enter

STARTUP OPEN sales PFILE=INITSALES.ORA RESTRICT

where SALES is the database name specified in the DB_NAME parameter in the INITSALES.ORA parameter file.

Database Shutdown

Shutting down a database involves three steps:

Closing the database

When a database is closed, all database and recovery data in the SGA are written to the datafiles and redo log files, and all online datafiles are closed.
Dismounting the database

Dismounting the database disassociates the database from an instance and closes the control files of the database.
Shutting down the instance

Shutting down an instance reclaims the SGA from memory and terminates the background Oracle Database processes that constitute an Oracle Database instance.

For more information about database shutdown, see the Oracle Database Concepts guide. For information about stopping a database, see the SHUTDOWN command.

Example 10-4 Shutting Down the Database

To shut down the database normally after it has been opened and mounted, enter

SHUTDOWN

Database closed.
Database dismounted.
ORACLE instance shut down.

Redo Log Files

Every Oracle database has a set of two or more redo log files. The set of redo log files for a database is collectively referred to as the database's redo log.

The redo log is used to record changes made to data. If, for example, there is a database failure, the redo log is used to recover the database. To protect against a failure involving the redo log itself, Oracle Database has a mirrored redo log so that two or more copies of the redo log can be maintained on different disks.

ARCHIVELOG Mode

Operating a database in ARCHIVELOG mode enables the archiving of the online redo log.

The SQL ALTER SYSTEM command enables a complete recovery from disk failure as well as instance failure, because all changes made to the database are permanently saved in an archived redo log.

For more information about redo log files and database archiving modes, see the Oracle Database Concepts manual, and the ARCHIVE LOG command.

To list the details of the current log file being archived, enter

ARCHIVE LOG LIST

Database log mode              Archive Mode 
Automatic archival             Enabled 
Archive destination            /vobs/oracle/dbs/arch 
Oldest online log sequence     221 
Next log sequence to archive   222 
Current log sequence           222

Database Recovery

If a damaged database is in ARCHIVELOG mode, it is a candidate for either complete media recovery or incomplete media recovery operations. To begin media recovery operations use the RECOVER command. For more information about recovering data, see the RECOVER command.

In order to begin recovery operations, you must have DBA privileges.

To recover the database up to a specified time using a control backup file, enter

RECOVER DATABASE UNTIL TIME '1998-11-23:12:47:30'-
USING BACKUP CONTROLFILE

To recover two offline tablespaces, enter

RECOVER TABLESPACE ts1, ts2

Make sure that the tablespaces you are interested in recovering have been taken offline, before proceeding with recovery for those tablespaces.