The catalog pg_listener supports the
LISTEN and
NOTIFY
commands. A listener creates an entry in
pg_listener for each notification name
it is listening for. A notifier scans pg_listener
and updates each matching entry to show that a notification has occurred.
The notifier also sends a signal (using the PID recorded in the table)
to awaken the listener from sleep.
Table 42-22. pg_listener Columns
| Name | Type | References | Description |
|---|
| relname | name | | Notify condition name. (The name need not match any actual
relation in the database; the name relname is historical.)
|
| listenerpid | int4 | | PID of the server process that created this entry. |
| notification | int4 | | Zero if no event is pending for this listener. If an event is
pending, the PID of the server process that sent the notification.
|