lmdb_table (5)

Contents

NAME
SYNOPSIS
DESCRIPTION
REQUESTS
RELIABILITY
SYNCHRONIZATION
CONFIGURATION PARAMETERS
SEE ALSO
README FILES
LICENSE
HISTORY
AUTHOR(S)

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 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
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 acquire an exclusive
lock between updating the database and starting 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 (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