slapd-mdb - Memory-Mapped DB backend to slapd
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
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
- 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.
- 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 /var/db/openldap/openldap-data.
- 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
- 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.
The mdb backend honors access control semantics as
indicated in slapd.access(5).
This is an early release; the database file format or other
characteristics may change incompatibly in future releases.
- default slapd configuration file
slapd.conf(5), slapd-config(5), slapd(8),
slapadd(8), slapcat(8), slapindex(8), OpenLDAP MDB
OpenLDAP Software is developed and maintained by The
OpenLDAP Project <http://www.openldap.org/>. OpenLDAP Software
is derived from University of Michigan LDAP 3.3 Release. Written by Howard