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#++
# NAME
# lmdb_table 5
# SUMMARY
# Postfix LMDB adapter
# SYNOPSIS
# \fBpostmap lmdb:/etc/postfix/\fIfilename\fR
# .br
# \fBpostmap -i lmdb:/etc/postfix/\fIfilename\fB <\fIinputfile\fR
#
# \fBpostmap -d "\fIkey\fB" lmdb:/etc/postfix/\fIfilename\fR
# .br
# \fBpostmap -d - lmdb:/etc/postfix/\fIfilename\fB <\fIinputfile\fR
#
# \fBpostmap -q "\fIkey\fB" lmdb:/etc/postfix/\fIfilename\fR
# .br
# \fBpostmap -q - lmdb:/etc/postfix/\fIfilename\fB <\fIinputfile\fR
# 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
# .ad
# .fi
# 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 "\fBpostfix reload\fR".
# RELIABILITY
# .ad
# .fi
# 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
# .ad
# .fi
# 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
# .ad
# .fi
# Short-lived programs automatically pick up changes to
# main.cf. With long-running daemon programs, Use the command
# "\fBpostfix reload\fR" after a configuration change.
# .IP "\fBlmdb_map_size (default: 16777216)\fR"
# 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
# .ad
# .fi
# Use "\fBpostconf readme_directory\fR" or
# "\fBpostconf html_directory\fR" to locate this information.
# .na
# .nf
# DATABASE_README, Postfix lookup table overview
# LMDB_README, Postfix OpenLDAP LMDB howto
# LICENSE
# .ad
# .fi
# 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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