LISTEN - listen for a notification
registers the current session as a
listener on the notification channel named
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
A session can be unregistered for a given notification channel with the
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
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,
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
Name of a notification channel (any identifier).
takes effect at transaction commit.
within a transaction that later rolls back, the set of notification
channels being listened to is unchanged.
A transaction that has executed
prepared for two-phase commit.
Configure and execute a listen/notify sequence from psql :
LISTEN virtual; NOTIFY virtual; Asynchronous notification "virtual" received from server process with PID 8448.
There is no
statement in the SQL