Provided by: slapd_2.4.28-1.1ubuntu4_i386 bug


       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 own.

       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 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.

              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

       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

       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


       The  mdb  backend  honors  access  control  semantics  as  indicated in


       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 documentation.


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