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listen -- listen for notification on a relation
listen
class_name
listen is used to register the current backend
as a listener on the relation class_name. When the command notify class_name
is called either from within a rule or at the query level, the frontend
applications corresponding to the listening backends are notified. When
the backend process exits, this registration is cleared.
This event notification
is performed through the Libpq protocol and frontend application interface.
The application program must explicitly poll a Libpq global variable,
PQAsyncNotifyWaiting, and call the routine PQnotifies in order to find
out the name of the class to which a given notification corresponds.
If this code is not included in the application, the event notification
will be queued and never be processed.
create rule(l)
, notify(l)
,
select(l)
, libpq.
There is no way to un-listen except to drop the
connection (i.e., restart the backend server).
The monitor(1)
command does
not poll for asynchronous events.
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