| slapd-mdb(5) - phpMan
SLAPD-MDB(5) File Formats Manual 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 lay‐
out 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 check‐
point. 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 con‐
figured 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 alloca‐
tion. Filters that are nested deeper than the search stack depth will cause a sepa‐
rate 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.openl‐
dap.org/>. OpenLDAP Software is derived from University of Michigan LDAP 3.3 Release.
Written by Howard Chu.
OpenLDAP 2014/09/20 SLAPD-MDB(5)
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