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man pages section 5: File Formats

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Updated: Wednesday, February 9, 2022

slapd-mdb (5oldap)


slapd-mdb - Mapped DB backend to slapd




SLAPD-MDB(5oldap)                                            SLAPD-MDB(5oldap)

       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.
       It is the recommended primary database backend.

       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/openl-

       envflags {nosync,nometasync,writemap,mapasync,nordahead}
              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.

                     Turn off file readahead. Usually the OS  performs  reada-
                     head on every read request. This usually boosts read per-
                     formance but can be harmful to random access read perfor-
                     mance 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  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.

       rtxnsize <entries>
              Specify the maximum number of entries to  process  in  a  single
              read  transaction when executing a large search. Long-lived read
              transactions prevent old database pages  from  being  reused  in
              write  transactions,  and so can cause significant growth of the
              database file when there is heavy write  traffic.  This  setting
              causes the read transaction in large searches to be released and
              reacquired after the given number of entries has been  read,  to
              give  writers the opportunity to reclaim old database pages. The
              default is 10000.

       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

              default slapd configuration file

       See attributes(7) for descriptions of the following attributes:

       |ATTRIBUTE TYPE |       ATTRIBUTE VALUE         |
       |Availability   | service/network/ldap/openldap |
       |Stability      | Pass-through uncommitted      |

       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
       <http://www.openldap.org/>.  OpenLDAP Software is derived from the Uni-
       versity of Michigan LDAP 3.3 Release.  Written by Howard Chu.

       Source  code  for open source software components in Oracle Solaris can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-

       This     software     was    built    from    source    available    at
       https://github.com/oracle/solaris-userland.   The  original   community
       source  was downloaded from  ftp://ftp.openldap.org/pub/OpenLDAP/openl-

       Further information about this software can be found on the open source
       community website at http://www.openldap.org/.

OpenLDAP 2.4.57                   2021/01/18                 SLAPD-MDB(5oldap)