The pg_listener system catalog table 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 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.

This table is not currently used in HAWQ.

Table 1. pg_catalog.pg_listener

column type references description
relname name   Notify condition name. (The name need not match any actual relation in the database.
listenerpid integer   PID of the server process that created this entry.
notification integer   Zero if no event is pending for this listener. If an event is pending, the PID of the server process that sent the notification.