LMDB_TABLE
Section: File Formats (5)
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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
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 (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
Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- REQUESTS
-
- RELIABILITY
-
- SYNCHRONIZATION
-
- CONFIGURATION PARAMETERS
-
- SEE ALSO
-
- README FILES
-
- LICENSE
-
- HISTORY
-
- AUTHOR(S)
-
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