LMDB_TABLE(5)                                                    LMDB_TABLE(5)

       lmdb_table - Postfix LMDB adapter

       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

       The  Postfix  LMDB  adapter  provides  access  to  a  persistent,  mem-
       ory-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.

       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.

       Changes to an LMDB database do not trigger an automatic daemon restart,
       and do not require a daemon restart with "postfix reload".

       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 corruption 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.

       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 hold an exclusive lock while opening 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.

       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 (16777216)
              The initial OpenLDAP LMDB database size limit in bytes.

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

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

       The Secure Mailer license must be distributed with this software.

       LMDB support was introduced with Postfix version 2.11.

       Howard Chu
       Symas Corporation

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

       Wietse Venema
       Google, Inc.
       111 8th Avenue
       New York, NY 10011, USA