    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 lmdb:, cdb:, hash:,  or  dbm:
           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 post-
                  fix 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  informa-
                  tion  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  ver-
                  ify(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_digest (default: empty)
                  After  processing  the  key_format setting, and before sending a
                  request to the memcache server, run the key  through  the  named
                  message  digest  algorithm  and  convert the result to lowercase
                  hexadecimal characters. This prevents a  database  access  error
                  when  keys  may  exceed  the  memcache server's key length limit
                  (usually, 250 bytes). Specify the name of a message digest algo-
                  rithm that is supported by OpenSSL, for example, sha256.

                  This  feature  is  available  in  Postfix  3.11  and  later, and
                  requires that Postfix is built with TLS support.

           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.  Other-
                         wise, 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 corre-
                         sponding 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_mail-
           box_maps (these specify UNIX process privileges for "/file/name" desti-
           nations).   In  a typical deployment a memcache database is writable by
           any process that can talk to the memcache server;  in  contrast,  secu-
           rity-sensitive  tables must never be writable by the unprivileged Post-
           fix 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
           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)