    LMDB_TABLE(5)                                                    LMDB_TABLE(5)

    NAME
           lmdb_table - Postfix LMDB adapter

    SYNOPSIS
           postmap lmdb:/etc/postfix/filename
           postmap -i lmdb:/etc/postfix/filename <inputfile

           postmap -d "key" lmdb:/etc/postfix/filename
           postmap -d - lmdb:/etc/postfix/filename <inputfile

           postmap -q "key" lmdb:/etc/postfix/filename
           postmap -q - lmdb:/etc/postfix/filename <inputfile

    DESCRIPTION
           The  Postfix  LMDB  adapter  provides  access  to a persistent, memory-
           mapped, key-value store.  The database size is limited only by the size
           of  the  memory  address  space  (typically  31 or 47 bits on 32-bit or
           64-bit CPUs, respectively) and by the available file system space.

    REQUESTS
           The LMDB adapter supports all Postfix lookup  table  operations.   This
           makes  LMDB  suitable  for  Postfix  address rewriting, routing, access
           policies, caches, or any information that can be stored under  a  fixed
           lookup key.

           When  a  transaction  fails due to a full database, Postfix resizes the
           database and retries the transaction.

           Postfix table lookups may generate partial search keys such  as  domain
           names  without one or more subdomains, network addresses without one or
           more least-significant octets, or email addresses  without  the  local-
           part, address extension or domain portion.  This behavior is also found
           with, for example, btree:, hash:, or ldap: tables.

           Unlike other flat-file Postfix databases, changes to an  LMDB  database
           do  not  trigger  automatic  daemon program restart, and do not require
           "postfix reload".

    RELIABILITY
           LMDB's copy-on-write architecture provides safe updates, at the cost of
           using  more space than some other flat-file databases.  Read operations
           are memory-mapped for speed.  Write operations are not memory-mapped to
           avoid silent curruption due to stray pointer bugs.

           Multiple processes can safely update an LMDB database without serializ-
           ing requests through the proxymap(8) service.  This makes LMDB suitable
           as a shared cache for verify(8) or postscreen(8) services.

    SYNCHRONIZATION
           The  Postfix  LMDB adapter does not use LMDB's built-in locking scheme,
           because that would require world-writable lockfiles and  would  violate
           the  Postfix security model.  Instead, Postfix uses fcntl(2) locks with
           whole-file granularity.  Programs that use LMDB's built-in locking pro-
           tocol will corrupt a Postfix LMDB database or will read garbage.

           Every Postfix LMDB database read or write transaction must be protected
           from start to end with a shared or exclusive fcntl(2) lock.   A  writer
           may  atomically  downgrade  an  exclusive lock to a shared lock, but it
           must acquire an exclusive lock between updating the database and start-
           ing another write transaction.

           Note  that  fcntl(2)  locks do not protect transactions within the same
           process against each other.  If a program cannot avoid making  simulta-
           neous database requests, then it must protect its transactions with in-
           process locks, in addition to the per-process fcntl(2) locks.

    CONFIGURATION PARAMETERS
           Short-lived programs automatically pick up changes  to  main.cf.   With
           long-running  daemon programs, Use the command "postfix reload" after a
           configuration change.

           lmdb_map_size (default: 16777216)
                  The initial LMDB database size limit in bytes.

    SEE ALSO
           postconf(1), Postfix supported lookup tables
           postmap(1), Postfix lookup table maintenance
           postconf(5), configuration parameters

    README FILES
           DATABASE_README, Postfix lookup table overview
           LMDB_README, Postfix OpenLDAP LMDB howto

    LICENSE
           The Secure Mailer license must be distributed with this software.

    HISTORY
           LMDB support was introduced with Postfix version 2.11.

    AUTHOR(S)
           Howard Chu
           Symas Corporation

           Wietse Venema
           IBM T.J. Watson Research
           P.O. Box 704
           Yorktown Heights, NY 10598, USA

                                                                     LMDB_TABLE(5)