LMDB_TABLE(5)LMDB_TABLE(5)NAMElmdb_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 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 curruption 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 acquire an exclusive lock between updating the database and start‐
ing 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 ALSOpostconf(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)
