43.20. pg_listener

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 43-20. pg_listener Columns

relnamename Notify condition name. (The name need not match any actual relation in the database; the name relname is historical.)
listenerpidint4 PID of the server process that created this entry.
notificationint4  Zero if no event is pending for this listener. If an event is pending, the PID of the server process that sent the notification.