Notify
Signals all backends that are listening for the specified notify event.
Synopsis
NOTIFY nameParameters
nameThe condition to be signaled.
Results
NOTIFYThe 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 ...