Practical PostgreSQL

Notify

Signals all backends that are listening for the specified notify event.

Synopsis

NOTIFY name

Parameters

name

The condition to be signaled.

Results

NOTIFY

The message returned when a notification is sent out correctly.

Description

The NOTIFY command is the counterpart of the LISTEN command, which we covered earlier in this chapter. The two commands provide a simple interprocess communication (IPC) implementation that can often prove useful if used correctly.

Use NOTIFY to send out a notification with the specified name; if any frontends have issued a LISTEN command with the same notification name, they will be informed of the notification.

Note

The behavior of a frontend process after receiving a notification sent by the NOTIFY command is dependent upon its implementation of the feature, so it may not respond immediately (or at all).

A notification is comprised of the notification’s name and the issuing backend’s process ID (PID). The original designer of the database specifies what notify condition names exist and how they function within the database.

The NOTIFY and LISTEN commands are most often used to provide a way to notify frontend processes that tables have been modified; as such, notification names are often set to the names of tables. This is the common use of this feature, but it is not required that notification names be table names.

Note

Automatic notification of table modifications ...