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
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
command. A sessions listen registrations are automatically cleared when the session ends.
The method a client application must use to detect notification events depends on which
application programming interface it uses. With the
library, the application issues
as an ordinary SQL command, and then must periodically call the function
to find out whether any notification events have been received. Other interfaces such as
provide higher-level methods for handling notify events; indeed, with
the application programmer should not even issue
directly. See the documentation for the interface you are using for more details.
contains a more extensive discussion of the use of
takes effect at transaction commit. If
is executed within a transaction that later rolls back, the set of notification channels being listened to is unchanged.
A transaction that has executed
cannot be prepared for two-phase commit.