    SCACHE(8)                                                            SCACHE(8)

    NAME
           scache - Postfix shared connection cache server

    SYNOPSIS
           scache [generic Postfix daemon options]

    DESCRIPTION
           The  scache(8)  server  maintains a shared multi-connection cache. This
           information can be used by, for example, Postfix SMTP clients or  other
           Postfix delivery agents.

           The connection cache is organized into logical destination names, phys-
           ical endpoint names, and connections.

           As a specific example, logical SMTP  destinations  specify  (transport,
           domain,  port),  and  physical  SMTP  endpoints  specify (transport, IP
           address, port).  An SMTP connection may be  saved  after  a  successful
           mail transaction.

           In  the general case, one logical destination may refer to zero or more
           physical endpoints, one physical endpoint may be referenced by zero  or
           more  logical  destinations, and one endpoint may refer to zero or more
           connections.

           The exact syntax of a logical destination or endpoint name is  applica-
           tion  dependent;  the  scache(8) server does not care.  A connection is
           stored as a file descriptor together with application-dependent  infor-
           mation  that  is  needed to re-activate a connection object. Again, the
           scache(8) server is completely unaware of the details of that  informa-
           tion.

           All  information  is stored with a finite time to live (ttl).  The con-
           nection cache  daemon  terminates  when  no  client  is  connected  for
           max_idle time units.

           This server implements the following requests:

           save_endp ttl endpoint endpoint_properties file_descriptor
                  Save  the specified file descriptor and connection property data
                  under the specified endpoint name. The endpoint  properties  are
                  used  by  the  client  to  re-activate  a  passivated connection
                  object.

           find_endp endpoint
                  Look up cached properties and a cached file descriptor  for  the
                  specified endpoint.

           save_dest ttl destination destination_properties endpoint
                  Save  the  binding between a logical destination and an endpoint
                  under the destination name, together with  destination  specific
                  connection  properties.  The  destination properties are used by
                  the client to re-activate a passivated connection object.

           find_dest destination
                  Look up cached destination properties, cached  endpoint  proper-
                  ties,  and  a  cached  file descriptor for the specified logical
                  destination.

    SECURITY
           The scache(8) server is not security-sensitive. It does not talk to the
           network, and it does not talk to local users.  The scache(8) server can
           run chrooted at fixed low privilege.

           The scache(8) server is not a trusted process. It must not be  used  to
           store information that is security sensitive.

    DIAGNOSTICS
           Problems and transactions are logged to syslogd(8).

    BUGS
           The session cache cannot be shared among multiple machines.

           When  a  connection  expires  from  the cache, it is closed without the
           appropriate protocol specific handshake.

    CONFIGURATION PARAMETERS
           Changes to main.cf are picked up automatically as  scache(8)  processes
           run for only a limited amount of time. Use the command "postfix reload"
           to speed up a change.

           The text below provides only a parameter summary. See  postconf(5)  for
           more details including examples.

    RESOURCE CONTROLS
           connection_cache_ttl_limit (2s)
                  The  maximal  time-to-live  value  that the scache(8) connection
                  cache server allows.

           connection_cache_status_update_time (600s)
                  How frequently the scache(8) server logs usage  statistics  with
                  connection cache hit and miss rates for logical destinations and
                  for physical endpoints.

    MISCELLANEOUS CONTROLS
           config_directory (see 'postconf -d' output)
                  The default location of the Postfix main.cf and  master.cf  con-
                  figuration files.

           daemon_timeout (18000s)
                  How  much  time  a  Postfix  daemon process may take to handle a
                  request before it is terminated by a built-in watchdog timer.

           ipc_timeout (3600s)
                  The time limit for sending  or  receiving  information  over  an
                  internal communication channel.

           max_idle (100s)
                  The  maximum  amount of time that an idle Postfix daemon process
                  waits for an incoming connection before terminating voluntarily.

           process_id (read-only)
                  The process ID of a Postfix command or daemon process.

           process_name (read-only)
                  The process name of a Postfix command or daemon process.

           syslog_facility (mail)
                  The syslog facility of Postfix logging.

           syslog_name (see 'postconf -d' output)
                  The  mail  system  name that is prepended to the process name in
                  syslog records, so that "smtpd"  becomes,  for  example,  "post-
                  fix/smtpd".

    SEE ALSO
           smtp(8), SMTP client
           postconf(5), configuration parameters
           master(8), process manager
           syslogd(8), system logging

    README FILES
           CONNECTION_CACHE_README, Postfix connection cache

    LICENSE
           The Secure Mailer license must be distributed with this software.

    HISTORY
           This service was introduced with Postfix version 2.2.

    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

                                                                         SCACHE(8)