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LMDB_TABLE(5)            DragonFly File Formats Manual           LMDB_TABLE(5)


NAME

       lmdb_table - Postfix LMDB adapter


SYNOPSIS

       postmap lmdb:$config_directory/filename
       postmap -i lmdb:$config_directory/filename <inputfile

       postmap -d "key" lmdb:$config_directory/filename
       postmap -d - lmdb:$config_directory/filename <inputfile

       postmap -q "key" lmdb:$config_directory/filename
       postmap -q - lmdb:$config_directory/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.

       Changes to an LMDB database do not trigger an automatic daemon restart,
       and do not require a daemon restart with "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
       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 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
       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 (16777216)
              The initial OpenLDAP 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)

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