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.

OpenLDAP                                           2015/08/14                                       SLAPD-MDB(5)