216 lines
7.5 KiB
Groff
216 lines
7.5 KiB
Groff
.lf 1 stdin
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.TH SLAPD-MDB 5 "2020/04/28" "OpenLDAP 2.4.50"
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.\" Copyright 2011-2020 The OpenLDAP Foundation All Rights Reserved.
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.\" Copying restrictions apply. See COPYRIGHT/LICENSE.
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.\" $OpenLDAP$
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.SH NAME
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slapd\-mdb \- Memory-Mapped DB backend to slapd
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.SH SYNOPSIS
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.B /etc/openldap/slapd.conf
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.SH DESCRIPTION
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The \fBmdb\fP backend to
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.BR slapd (8)
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uses OpenLDAP's Lightning Memory-Mapped DB (LMDB) library to store data.
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It relies completely on the underlying operating system for memory
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management and does no caching of its own. It is the recommended
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primary database backend.
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.LP
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The \fBmdb\fP backend is similar to the \fBhdb\fP backend in that
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it uses a hierarchical database layout which
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supports subtree renames. It is both more space-efficient and more
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execution-efficient than the \fBbdb\fP backend, while being overall
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much simpler to manage.
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.SH CONFIGURATION
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These
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.B slapd.conf
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options apply to the \fBmdb\fP backend database.
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That is, they must follow a "database mdb" line and
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come before any subsequent "backend" or "database" lines.
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Other database options are described in the
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.BR slapd.conf (5)
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manual page.
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.TP
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.BI checkpoint \ <kbyte>\ <min>
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Specify the frequency for flushing the database disk buffers.
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This setting is only needed if the \fBdbnosync\fP option is used.
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The checkpoint will occur if either \fI<kbyte>\fP data has been written or
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\fI<min>\fP minutes have passed since the last checkpoint.
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Both arguments default to zero, in which case they are ignored. When
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the \fI<min>\fP argument is non-zero, an internal task will run every
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\fI<min>\fP minutes to perform the checkpoint.
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Note: currently the \fI<kbyte>\fP setting is unimplemented.
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.TP
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.B dbnosync
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Specify that on-disk database contents should not be immediately
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synchronized with in memory changes.
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Enabling this option may improve performance at the expense of data
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security. In particular, if the operating system crashes before changes are
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flushed, some number of transactions may be lost.
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By default, a full data flush/sync is performed when each
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transaction is committed.
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.TP
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.BI directory \ <directory>
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Specify the directory where the LMDB files containing this database and
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associated indexes live.
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A separate directory must be specified for each database.
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The default is
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.BR /var/openldap/openldap\-data .
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.TP
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\fBenvflags \fR{\fBnosync\fR,\fBnometasync\fR,\fBwritemap\fR,\fBmapasync\fR,\fBnordahead\fR}
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Specify flags for finer-grained control of the LMDB library's operation.
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.RS
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.TP
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.B nosync
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This is exactly the same as the
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.I dbnosync
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directive.
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.RE
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.RS
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.TP
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.B nometasync
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Flush the data on a commit, but skip the sync of the meta page. This mode is
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slightly faster than doing a full sync, but can potentially lose the last
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committed transaction if the operating system crashes. If both
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.I nometasync
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and
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.I nosync
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are set, the
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.I nosync
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flag takes precedence.
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.RE
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.RS
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.TP
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.B writemap
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Use a writable memory map instead of just read-only. This speeds up write operations
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but makes the database vulnerable to corruption in case any bugs in slapd
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cause stray writes into the mmap region.
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.RE
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.RS
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.TP
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.B mapasync
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When using a writable memory map and performing flushes on each commit, use an
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asynchronous flush instead of a synchronous flush (the default). This option
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has no effect if
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.I writemap
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has not been set. It also has no effect if
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.I nosync
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is set.
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.RE
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.RS
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.TP
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.B nordahead
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Turn off file readahead. Usually the OS performs readahead on every read
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request. This usually boosts read performance but can be harmful to
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random access read performance if the system's memory is full and the DB
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is larger than RAM. This option is not implemented on Windows.
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.RE
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.TP
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\fBindex \fR{\fI<attrlist>\fR|\fBdefault\fR} [\fBpres\fR,\fBeq\fR,\fBapprox\fR,\fBsub\fR,\fI<special>\fR]
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Specify the indexes to maintain for the given attribute (or
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list of attributes).
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Some attributes only support a subset of indexes.
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If only an \fI<attr>\fP is given, the indices specified for \fBdefault\fR
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are maintained.
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Note that setting a default does not imply that all attributes will be
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indexed. Also, for best performance, an
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.B eq
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index should always be configured for the
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.B objectClass
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attribute.
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A number of special index parameters may be specified.
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The index type
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.B sub
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can be decomposed into
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.BR subinitial ,
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.BR subany ,\ and
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.B subfinal
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indices.
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The special type
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.B nolang
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may be specified to disallow use of this index by language subtypes.
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The special type
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.B nosubtypes
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may be specified to disallow use of this index by named subtypes.
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Note: changing \fBindex\fP settings in
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.BR slapd.conf (5)
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requires rebuilding indices, see
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.BR slapindex (8);
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changing \fBindex\fP settings
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dynamically by LDAPModifying "cn=config" automatically causes rebuilding
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of the indices online in a background task.
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.TP
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.BI maxreaders \ <integer>
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Specify the maximum number of threads that may have concurrent read access
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to the database. Tools such as slapcat count as a single thread,
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in addition to threads in any active slapd processes. The
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default is 126.
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.TP
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.BI maxsize \ <bytes>
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Specify the maximum size of the database in bytes. A memory map of this
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size is allocated at startup time and the database will not be allowed
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to grow beyond this size. The default is 10485760 bytes. This setting
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may be changed upward if the configured limit needs to be increased.
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Note: It is important to set this to as large a value as possible,
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(relative to anticipated growth of the actual data over time) since
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growing the size later may not be practical when the system is under
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heavy load.
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.TP
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.BI mode \ <integer>
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Specify the file protection mode that newly created database
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files should have.
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The default is 0600.
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.TP
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.BI rtxnsize \ <entries>
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Specify the maximum number of entries to process in a single read
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transaction when executing a large search. Long-lived read transactions
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prevent old database pages from being reused in write transactions, and
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so can cause significant growth of the database file when there is
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heavy write traffic. This setting causes the read transaction in
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large searches to be released and reacquired after the given number
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of entries has been read, to give writers the opportunity to
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reclaim old database pages. The default is 10000.
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.TP
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.BI searchstack \ <depth>
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Specify the depth of the stack used for search filter evaluation.
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Search filters are evaluated on a stack to accommodate nested AND / OR
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clauses. An individual stack is assigned to each server thread.
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The depth of the stack determines how complex a filter can be
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evaluated without requiring any additional memory allocation. Filters that
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are nested deeper than the search stack depth will cause a separate
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stack to be allocated for that particular search operation. These
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allocations can have a major negative impact on server performance,
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but specifying too much stack will also consume a great deal of memory.
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Each search stack uses 512K bytes per level. The default stack depth
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is 16, thus 8MB per thread is used.
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.SH ACCESS CONTROL
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The
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.B mdb
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backend honors access control semantics as indicated in
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.BR slapd.access (5).
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.SH FILES
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.TP
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.B /etc/openldap/slapd.conf
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default
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.B slapd
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configuration file
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.SH SEE ALSO
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.BR slapd.conf (5),
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.BR slapd\-config (5),
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.BR slapd (8),
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.BR slapadd (8),
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.BR slapcat (8),
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.BR slapindex (8),
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OpenLDAP LMDB documentation.
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.SH ACKNOWLEDGEMENTS
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.lf 1 ./../Project
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.\" Shared Project Acknowledgement Text
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.B "OpenLDAP Software"
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is developed and maintained by The OpenLDAP Project <http://www.openldap.org/>.
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.B "OpenLDAP Software"
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is derived from the University of Michigan LDAP 3.3 Release.
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.lf 208 stdin
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Written by Howard Chu.
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