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 localpart, 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 serializing 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 protocol 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 starting 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 simultaneous 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

       Use "postconf readme_directory" or "postconf html_directory" to locate this information.
       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)