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LMDB_TABLE(5)                 File Formats Manual                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,  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.
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 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.
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 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.
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
       Wietse Venema
       Google, Inc.
       111 8th Avenue
       New York, NY 10011, USA

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