listen(7) [centos man page]

LISTEN(7)						  PostgreSQL 9.2.7 Documentation						 LISTEN(7)

NAME

       LISTEN - listen for a notification

SYNOPSIS

       LISTEN channel

DESCRIPTION

       LISTEN registers the current session as a listener on the notification channel named channel. If the current session is already registered
       as a listener for this notification channel, nothing is done.

       Whenever the command NOTIFY channel is invoked, either by this session or another one connected to the same database, all the sessions
       currently listening on that notification channel are notified, and each will in turn notify its connected client application.

       A session can be unregistered for a given notification channel with the UNLISTEN command. A session's listen registrations are
       automatically cleared when the session ends.

       The method a client application must use to detect notification events depends on which PostgreSQL application programming interface it
       uses. With the libpq library, the application issues LISTEN as an ordinary SQL command, and then must periodically call the function
       PQnotifies to find out whether any notification events have been received. Other interfaces such as libpgtcl provide higher-level methods
       for handling notify events; indeed, with libpgtcl the application programmer should not even issue LISTEN or UNLISTEN directly. See the
       documentation for the interface you are using for more details.

       NOTIFY(7) contains a more extensive discussion of the use of LISTEN and NOTIFY.

PARAMETERS

       channel
	   Name of a notification channel (any identifier).

NOTES

       LISTEN takes effect at transaction commit. If LISTEN or UNLISTEN is executed within a transaction that later rolls back, the set of
       notification channels being listened to is unchanged.

       A transaction that has executed LISTEN cannot be prepared for two-phase commit.

EXAMPLES

       Configure and execute a listen/notify sequence from psql:

	   LISTEN virtual;
	   NOTIFY virtual;
	   Asynchronous notification "virtual" received from server process with PID 8448.

COMPATIBILITY

       There is no LISTEN statement in the SQL standard.

SEE ALSO

       NOTIFY(7), UNLISTEN(7)

PostgreSQL 9.2.7						    2014-02-17								 LISTEN(7)

LISTEN(7)							   SQL Commands 							 LISTEN(7)

NAME

       LISTEN - listen for a notification

SYNOPSIS

       LISTEN name

   INPUTS
       name   Name of notify condition.

   OUTPUTS
       LISTEN Message returned upon successful completion of registration.

       WARNING: Async_Listen: We are already listening on name
	      If this backend is already registered for that notify condition.

DESCRIPTION

       LISTEN registers the current PostgreSQL backend as a listener on the notify condition name.

       Whenever  the  command  NOTIFY name is invoked, either by this backend or another one connected to the same database, all the backends cur-
       rently listening on that notify condition are notified, and each will in turn notify its connected frontend application. See the discussion
       of NOTIFY for more information.

       A  backend can be unregistered for a given notify condition with the UNLISTEN command. Also, a backend's listen registrations are automati-
       cally cleared when the backend process exits.

       The method a frontend application must use to detect notify events depends on which PostgreSQL application programming interface  it  uses.
       With the libpq library, the application issues LISTEN as an ordinary SQL command, and then must periodically call the routine PQnotifies to
       find out whether any notify events have been received. Other interfaces such as libpgtcl provide higher-level methods for  handling  notify
       events;	indeed,  with libpgtcl the application programmer should not even issue LISTEN or UNLISTEN directly. See the documentation for the
       library you are using for more details.

       NOTIFY [notify(7)] contains a more extensive discussion of the use of LISTEN and NOTIFY.

   NOTES
       name can be any string valid as a name; it need not correspond to the name of any actual table. If notifyname is enclosed in double-quotes,
       it need not even be a syntactically valid name, but can be any string up to 63 characters long.

       In  some  previous  releases of PostgreSQL, name had to be enclosed in double-quotes when it did not correspond to any existing table name,
       even if syntactically valid as a name. That is no longer required.

USAGE

       Configure and execute a listen/notify sequence from psql:

       LISTEN virtual;
       NOTIFY virtual;

       Asynchronous NOTIFY 'virtual' from backend with pid '8448' received.

COMPATIBILITY

   SQL92
       There is no LISTEN in SQL92.

SQL - Language Statements					    2002-11-22								 LISTEN(7)