Postfix manual - lmdb_table(5)

LMDB_TABLE(5) 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.
 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 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 therefore vio-
 late 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 process
 may atomically downgrade an exclusive lock to a shared lock before
 opening a database read transaction, but it must hold an exclusive lock
 while opening a 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 (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 
 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)