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NAME | SYNOPSIS | DESCRIPTION | CONFIGURATION | ACCESS CONTROL | FILES | SEE ALSO | ACKNOWLEDGEMENTS | COLOPHON |
SLAPD-MDB(5) File Formats Manual SLAPD-MDB(5)
slapd-mdb - Memory-Mapped DB backend to slapd
ETCDIR/slapd.conf
The mdb backend to slapd(8) uses OpenLDAP's Lightning Memory-Mapped
DB (LMDB) library to store data. It relies completely on the
underlying operating system for memory management and does no caching
of its own. It is the recommended primary database backend.
The mdb backend is similar to the hdb backend in that it uses a
hierarchical database layout which supports subtree renames. It is
both more space-efficient and more execution-efficient than the bdb
backend, while being overall much simpler to manage.
These slapd.conf options apply to the mdb backend database. That is,
they must follow a "database mdb" line and come before any subsequent
"backend" or "database" lines. Other database options are described
in the slapd.conf(5) manual page.
checkpoint <kbyte> <min>
Specify the frequency for flushing the database disk buffers.
This setting is only needed if the dbnosync option is used.
The checkpoint will occur if either <kbyte> data has been
written or <min> minutes have passed since the last
checkpoint. Both arguments default to zero, in which case
they are ignored. When the <min> argument is non-zero, an
internal task will run every <min> minutes to perform the
checkpoint. Note: currently the <kbyte> setting is
unimplemented.
dbnosync
Specify that on-disk database contents should not be
immediately synchronized with in memory changes. Enabling
this option may improve performance at the expense of data
security. In particular, if the operating system crashes
before changes are flushed, some number of transactions may be
lost. By default, a full data flush/sync is performed when
each transaction is committed.
directory <directory>
Specify the directory where the LMDB files containing this
database and associated indexes live. A separate directory
must be specified for each database. The default is
LOCALSTATEDIR/openldap-data.
envflags {nosync,nometasync,writemap,mapasync,nordahead}
Specify flags for finer-grained control of the LMDB library's
operation.
nosync This is exactly the same as the dbnosync directive.
nometasync
Flush the data on a commit, but skip the sync of the
meta page. This mode is slightly faster than doing a
full sync, but can potentially lose the last committed
transaction if the operating system crashes. If both
nometasync and nosync are set, the nosync flag takes
precedence.
writemap
Use a writable memory map instead of just read-only.
This speeds up write operations but makes the database
vulnerable to corruption in case any bugs in slapd
cause stray writes into the mmap region.
mapasync
When using a writable memory map and performing flushes
on each commit, use an asynchronous flush instead of a
synchronous flush (the default). This option has no
effect if writemap has not been set. It also has no
effect if nosync is set.
nordahead
Turn off file readahead. Usually the OS performs
readahead on every read request. This usually boosts
read performance but can be harmful to random access
read performance if the system's memory is full and the
DB is larger than RAM. This option is not implemented
on Windows.
index {<attrlist>|default} [pres,eq,approx,sub,<special>]
Specify the indexes to maintain for the given attribute (or
list of attributes). Some attributes only support a subset of
indexes. If only an <attr> is given, the indices specified
for default are maintained. Note that setting a default does
not imply that all attributes will be indexed. Also, for best
performance, an eq index should always be configured for the
objectClass attribute.
A number of special index parameters may be specified. The
index type sub can be decomposed into subinitial, subany, and
subfinal indices. The special type nolang may be specified to
disallow use of this index by language subtypes. The special
type nosubtypes may be specified to disallow use of this index
by named subtypes. Note: changing index settings in
slapindex(8);
changing index settings dynamically by LDAPModifying
"cn=config" automatically causes rebuilding of the indices
online in a background task.
maxentrysize <bytes>
Specify the maximum size of an entry in bytes. Attempts to
store an entry larger than this size will be rejected with the
error LDAP_ADMINLIMIT_EXCEEDED. The default is 0, which is
unlimited.
maxreaders <integer>
Specify the maximum number of threads that may have concurrent
read access to the database. Tools such as slapcat count as a
single thread, in addition to threads in any active slapd
processes. The default is 126.
maxsize <bytes>
Specify the maximum size of the database in bytes. A memory
map of this size is allocated at startup time and the database
will not be allowed to grow beyond this size. The default is
10485760 bytes. This setting may be changed upward if the
configured limit needs to be increased.
Note: It is important to set this to as large a value as
possible, (relative to anticipated growth of the actual data
over time) since growing the size later may not be practical
when the system is under heavy load.
mode <integer>
Specify the file protection mode that newly created database
files should have. The default is 0600.
multival_hi <integer>
Specify the number of values above which a multivalued
attribute is stored in a separate table. Normally entries are
stored as a single blob inside the database. When an entry
gets very large or contains attributes with a very large
number of values, modifications on that entry may get very
slow. Splitting the large attributes out to a separate table
can improve the performance of modification operations. The
default is UINT_MAX, which keeps all attributes in the main
blob.
multival_lo <integer>
Specify the number of values below which a multivalued
attribute that was stored in a separate table is moved back
into the main entry blob. If a modification deletes enough
values to bring an attribute below this threshold, its values
will be removed from the separate table and merged back into
the main entry blob. The default is UINT_MAX, which keeps all
attributes in the main blob.
rtxnsize <entries>
Specify the maximum number of entries to process in a single
read transaction when executing a large search. Long-lived
read transactions prevent old database pages from being reused
in write transactions, and so can cause significant growth of
the database file when there is heavy write traffic. This
setting causes the read transaction in large searches to be
released and reacquired after the given number of entries has
been read, to give writers the opportunity to reclaim old
database pages. The default is 10000.
searchstack <depth>
Specify the depth of the stack used for search filter
evaluation. Search filters are evaluated on a stack to
accommodate nested AND / OR clauses. An individual stack is
assigned to each server thread. The depth of the stack
determines how complex a filter can be evaluated without
requiring any additional memory allocation. Filters that are
nested deeper than the search stack depth will cause a
separate stack to be allocated for that particular search
operation. These allocations can have a major negative impact
on server performance, but specifying too much stack will also
consume a great deal of memory. Each search stack uses 512K
bytes per level. The default stack depth is 16, thus 8MB per
thread is used.
The mdb backend honors access control semantics as indicated in
slapd.access(5).
ETCDIR/slapd.conf
default slapd configuration file
slapd.conf(5), slapd-config(5), slapd(8), slapadd(8), slapcat(8),
slapindex(8), OpenLDAP LMDB documentation.
OpenLDAP Software is developed and maintained by The OpenLDAP Project
<http://www.openldap.org/>. OpenLDAP Software is derived from the
University of Michigan LDAP 3.3 Release. Written by Howard Chu.
This page is part of the OpenLDAP (an open source implementation of
the Lightweight Directory Access Protocol) project. Information
about the project can be found at ⟨http://www.openldap.org/⟩. If you
have a bug report for this manual page, see
⟨http://www.openldap.org/its/⟩. This page was obtained from the
project's upstream Git repository
⟨git://git.openldap.org/openldap.git⟩ on 2017-07-05. If you discover
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you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
OpenLDAP LDVERSION RELEASEDATE SLAPD-MDB(5)
Pages that refer to this page: slapd.backends(5), slapd-bdb(5), slapcat(8)