    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.
           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)