Provided by: postfix_3.8.6-1build2_amd64 
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. 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, update, delete and sequence (first/next) operations. The
sequence operation requires a backup database that supports the operation.
MEMCACHE MAIN PARAMETERS
memcache (default: inet:localhost:11211)
The memcache server (note: singular) that Postfix will try to connect to. For a TCP server
specify "inet:" followed by a hostname or address, ":", and a port name or number. Specify an
IPv6 address inside "[]". For a UNIX-domain server specify "unix:" followed by the socket
pathname. Examples:
memcache = inet:memcache.example.com:11211
memcache = inet:127.0.0.1:11211
memcache = inet:[fc00:8d00:189::3]:11211
memcache = unix:/path/to/socket
NOTE: to access a UNIX-domain socket with the proxymap(8) server, the socket must be accessible by
the unprivileged postfix user.
backup (default: undefined)
An optional Postfix database that provides persistent backup for the memcache database. The
Postfix memcache client will update the memcache database whenever it looks up or changes
information in the persistent database. Specify a Postfix "type:table" database. Examples:
# Non-shared postscreen cache.
backup = btree:/var/lib/postfix/postscreen_cache_map
# Shared postscreen cache for processes on the same host.
backup = proxy:btree:/var/lib/postfix/postscreen_cache_map
Access to remote proxymap servers is under development.
NOTE 1: When sharing a persistent postscreen(8) or verify(8) cache, disable automatic cache
cleanup (set *_cache_cleanup_interval = 0) except with one Postfix instance that will be
responsible for cache cleanup.
NOTE 2: When multiple tables share the same memcache database, each table should use the
key_format feature (see below) to prepend its own unique string to the lookup key. Otherwise,
automatic postscreen(8) or verify(8) cache cleanup may not work.
NOTE 3: When the backup database is accessed with "proxy:" lookups, the full backup database name
(including the "proxy:" prefix) must be specified in the proxymap server's proxy_read_maps or
proxy_write_maps setting (depending on whether the access is read-only or read-write).
flags (default: 0)
Optional flags that should be stored along with a memcache update. The flags are ignored when
looking up information.
ttl (default: 3600)
The expiration time in seconds of memcache updates.
NOTE 1: When using a memcache table as postscreen(8) or verify(8) cache without persistent backup,
specify a zero *_cache_cleanup_interval value with all Postfix instances that use the memcache,
and specify the largest postscreen(8) *_ttl value or verify(8) *_expire_time value as the memcache
table's ttl value.
NOTE 2: 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.
MEMCACHE KEY PARAMETERS
key_format (default: %s)
Format of the lookup and update keys that the Postfix memcache client sends to the memcache
server. By default, these are the same as the lookup and update keys that the memcache client
receives from Postfix applications.
NOTE 1: The key_format feature is not used for backup database requests.
NOTE 2: When multiple tables share the same memcache database, each table should prepend its own
unique string to the lookup key. Otherwise, automatic postscreen(8) or verify(8) cache cleanup
may not work.
Examples:
key_format = aliases:%s
key_format = verify:%s
key_format = postscreen:%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. Otherwise, %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 warning).
%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 parameter
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 user@mail.example.com, 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 specified patterns, a lookup is silently suppressed 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 "type:table" databases. 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
MEMCACHE ERROR CONTROLS
data_size_limit (default: 10240)
The maximal memcache reply data length in bytes.
line_size_limit (default: 1024)
The maximal memcache reply line length in bytes.
max_try (default: 2)
The number of times to try a memcache command before giving up. The memcache client does not
retry a command when the memcache server accepts no connection.
retry_pause (default: 1)
The time in seconds before retrying a failed memcache command.
timeout (default: 2)
The time limit for sending a memcache command and for receiving a memcache reply.
BUGS
The Postfix memcache client cannot be used for security-sensitive tables such as alias_maps (these may
contain "|command and "/file/name" destinations), or virtual_uid_maps, virtual_gid_maps and
virtual_mailbox_maps (these specify UNIX process privileges or "/file/name" destinations). In a typical
deployment a memcache database is writable by any process that can talk to the memcache server; in
contrast, security-sensitive tables must never be writable by the unprivileged Postfix user.
The Postfix memcache client requires additional configuration when used as postscreen(8) or verify(8)
cache. For details see the backup and ttl parameter discussions in the MEMCACHE MAIN PARAMETERS section
above.
SEE ALSO
postmap(1), Postfix lookup table manager
postconf(5), configuration parameters
README FILES
Use "postconf readme_directory" or "postconf html_directory" to locate this information.
DATABASE_README, Postfix lookup table overview
MEMCACHE_README, Postfix memcache client guide
LICENSE
The Secure Mailer license must be distributed with this software.
HISTORY
Memcache support was introduced with Postfix version 2.9.
AUTHOR(S)
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
MEMCACHE_TABLE(5)