|The PostgreSQL 9.0 Reference Manual - Volume 1B - SQL Command Reference
by The PostgreSQL Global Development Group
Paperback (6"x9"), 488 pages
RRP £14.95 ($19.95)
Sales of this book support the PostgreSQL project! Get a printed copy>>>
LISTEN -- listen for a notification
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
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
UNLISTEN 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).
LISTEN takes effect at transaction commit.
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.
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
LISTEN statement in the SQL
|ISBN 9781906966058||The PostgreSQL 9.0 Reference Manual - Volume 1B - SQL Command Reference||See the print edition|