SLAPD-MDB(5)

NAME
slapd-mdb - Memory-Mapped DB backend to slapd

SYNOPSIS
ETCDIR/slapd.conf

DESCRIPTION
The mdb backend to slapd(8) uses OpenLDAP's own Memory-Mapped DB (MDB) library to store data. It relies completely on the underlying operating system for memory management and does no caching of its own.

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.

CONFIGURATION
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 MDB files containing this database and associated indexes live. A separate directory must be specified for each database. The default is LOCALSTATEDIR/openldap-data.

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 slapd.conf(5) requires rebuilding indices, see slapindex(8); changing index settings dynamically by LDAPModifying "cn=config" automatically causes rebuilding of the indices online in a background task.

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.

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.

ACCESS CONTROL
The mdb backend honors access control semantics as indicated in slapd.access(5).

NOTES
This is an early release; the database file format or other characteristics may change incompatibly in future releases.

FILES

ETCDIR/slapd.conf
    default slapd configuration file

SEE ALSO
slapd.conf(5), slapd-config(5), slapd(8), slapadd(8), slapcat(8), slapindex(8), OpenLDAP MDB documentation.

ACKNOWLEDGEMENTS
Written by Howard Chu.