slapd-mdb(5)
NAME
slapd-mdb - Memory-Mapped DB backend to slapd
SYNOPSIS
/etc/ldap/slapd.conf
DESCRIPTION
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.
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 LMDB files containing this
database and associated indexes live. A separate directory must
be specified for each database. The default is /var/lib/ldap.
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
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).
FILES
/etc/ldap/slapd.conf
default slapd configuration file
SEE ALSO
slapd.conf(5), slapd-config(5), slapd(8), slapadd(8), slapcat(8),
slapindex(8), OpenLDAP LMDB documentation.
ACKNOWLEDGEMENTS
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 Chu.
Free and Open Source Software