Provided by: postfix_3.8.1-2ubuntu0.2_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)