MEMCACHE_TABLE(5) MEMCACHE_TABLE(5)
NAME
memcache_table - Postfix memcache client configuration
SYNOPSIS
postmap -q "string" memcache:/etc/postfix/filename
postmap -q - memcache:/etc/postfix/filename <inputfile
DESCRIPTION
The Postfix mail system uses optional tables for address
rewriting or mail routing. These tables are usually in dbm
or db format.
Alternatively, lookup tables can be specified as memcache
instances. In order to use memcache lookups, define a
memcache source as a lookup table in main.cf, for example:
virtual_alias_maps = memcache:/etc/postfix/memcache-aliases.cf
The file /etc/postfix/memcache-aliases.cf has the same
format as the Postfix main.cf file, and specifies the
parameters described below.
The Postfix memcache client supports the lookup and update
operations.
MEMCACHE PARAMETERS
hosts (default: localhost:11211)
The memcache servers that Postfix will try to con-
nect to. Specify a hostname or address, optionally
followed by ":" and a port name or number. The
default port is 11211. Examples:
hosts = memcache01.example.com
memcache02.example.com
key_format (default: %s)
Format of the lookup and update keys in memcache
queries. By default, these are the same as the
lookup and update keys that are given to the Post-
fix memcache client.
When the same memcache database is used to cache
information from multiple tables, you can use the
key_format feature to avoid name collisions by
prepending a fixed string. Examples:
key_format = aliases:%s
key_format = access:%s
The key_format parameter supports the following '%'
expansions:
%% This is replaced by a literal '%' character.
%s This is replaced by the memcache client
input key.
%u When the input key is an address of the form
user@domain, %u is replaced by the SQL
quoted local part of the address. Other-
wise, %u is replaced by the entire search
string. If the localpart is empty, a lookup
is silently suppressed and returns no
results (an update is skipped with a warn-
ing).
%d When the input key is an address of the form
user@domain, %d is replaced by the domain
part of the address. Otherwise, a lookup is
silently suppressed and returns no results
(an update is skipped with a warning).
%[SUD] The upper-case equivalents of the above
expansions behave in the key_format parame-
ter identically to their lower-case counter-
parts.
%[1-9] The patterns %1, %2, ... %9 are replaced by
the corresponding most significant component
of the input key's domain. If the input key
is [email protected], then %1 is com, %2
is example and %3 is mail. If the input key
is unqualified or does not have enough
domain components to satisfy all the speci-
fied patterns, a lookup is silently sup-
pressed and returns no results (an update is
skipped with a warning).
domain (default: no domain list)
This feature can significantly reduce database
server load. Specify a list of domain names, paths
to files, or dictionaries. When specified, only
fully qualified search keys with a *non-empty*
localpart and a matching domain are eligible for
lookup or update: bare 'user' lookups, bare domain
lookups and "@domain" lookups are silently skipped
(updates are skipped with a warning). Example:
domain = example.com, hash:/etc/postfix/searchdomains
flags (default: 0)
Optional flags that should be stored along with a
memcache update.
ttl (default: 604800)
The expiration time in seconds of memcache updates.
The default is one week.
When using memcache tables with postscreen(8) or
verify(8), specify a zero *_cache_cleanup_interval
value, and specify the largest postscreen(8) *_ttl
value or verify(8) *_expire_time value as the mem-
cache map's ttl value.
Note: according to memcache protocol documentation,
a value greater than 30 days (2592000 seconds)
specifies absolute UNIX time. Smaller values are
relative to the time of the update.
BUGS
The Postfix memcache client is based on libmemcache, which
will terminate its process after a memcache server goes
down. To avoid this, set up redundant memcache servers
that have no common source of failure.
The Postfix memcache client cannot be used for security-
sensitive tables such as alias_maps (these may contain
"|command and "/file/name" destinations), or vir-
tual_uid_maps and virtual_gid_maps (these specify UNIX
process privileges). In a typical deployment a memcache
database is shared via a TCP socket, and is therefore
writable not only by Postfix, but by any process that can
talk to the memcache server.
The Postfix memcache client requires additional configura-
tion when used with the postscreen(8) and verify(8) dae-
mons. For details see the ttl parameter discussion at the
end of the MEMCACHE PARAMETERS section in this document.
The Postfix memcache client is supported only with libmem-
cache version 1.4.0. Some libmemcache features are docu-
mented by reading libmemcache source code, instead a
proper API.
SEE ALSO
postmap(1), Postfix lookup table manager
postconf(5), configuration parameters
README FILES
DATABASE_README, Postfix lookup table overview
MEMCACHE_README, Postfix memcache client guide
LICENSE
The Secure Mailer license must be distributed with this
software.
HISTORY
The first memcache client for Postfix was written by Omar
Kilani. Besides being implemented on libmemcache, this
implementation bears no resemblance to his work.
AUTHOR(S)
Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
MEMCACHE_TABLE(5)