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, 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  opera-
       tions 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 serializing requests through the proxymap(8) service.  This makes LMDB suit-
       able 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 hold an exclusive lock while opening another write transac-
       tion.

       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

																     LMDB_TABLE(5)