42.22. pg_listener

## 42.22. `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 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.