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. |
