slapd-mdb - Memory-Mapped DB backend to slapd




       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.

       The mdb backend is similar to the hdb backend in that it uses a hierar-
       chical 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 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 argu-
              ments  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 particu-
              lar, 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 data-
              base and associated indexes live.  A separate directory must  be
              specified  for  each  database.   The default is /var/lib/openl-

       envflags {nosync,nometasync,writemap,mapasync}
              Specify flags for finer-grained control of  the  LMDB  library's

              nosync This is exactly the same as the dbnosync directive.

                     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 trans-
                     action if the operating system crashes. If  both  nometa-
                     sync  and  nosync  are  set, the nosync flag takes prece-

                     Use a writable memory map instead of just read-only. This
                     speeds up write operations but makes the database vulner-
                     able to corruption in case any bugs in slapd cause  stray
                     writes into the mmap region.

                     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.

       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 per-
              formance, 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 back-
              ground 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  pro-
              cesses. 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 possi-
              ble, (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 evalua-
              tion.  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 par-
              ticular 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


       This  is an early release; the database file format or other character-
       istics 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 LMDB documentation.


       OpenLDAP  Software  is developed and maintained by The OpenLDAP Project
       <>.  OpenLDAP Software is derived from  Univer-
       sity of Michigan LDAP 3.3 Release.  Written by Howard Chu.

OpenLDAP 2.4.36                   2013/08/17                      SLAPD-MDB(5)

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