LISTEN(7)		PostgreSQL 9.2.24 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 9.2.24		  2017-11-06			     LISTEN(7)