How to Use pg_notify in PostgreSQL for Notifications

Use pg_notify(channel, payload) in PostgreSQL to send a notification on a specified channel with an optional payload string. Other sessions can listen to this channel using LISTEN channel and receive notifications asynchronously.

Syntax

The pg_notify function sends a notification to all sessions listening on a specified channel.

• channel: The name of the notification channel (a string).
• payload: An optional string message sent with the notification (max 8000 bytes).

Example syntax:

sql

SELECT pg_notify('channel_name', 'your message here');

Example

This example shows how to send a notification and listen for it in two separate sessions.

Session 1 listens on the channel my_channel:

sql

-- Session 1: Listen for notifications
LISTEN my_channel;

-- Session 2: Send a notification
SELECT pg_notify('my_channel', 'Hello listeners!');

Output

Asynchronous notification "my_channel" with payload "Hello listeners!" received.

Common Pitfalls

Common mistakes when using pg_notify include:

• Not running LISTEN before expecting notifications.
• Expecting immediate synchronous results; notifications are asynchronous.
• Using channel names or payloads longer than allowed limits.
• Not handling notifications in client applications properly.

Example of a wrong approach and the correct way:

sql

-- Wrong: Sending notification without any session listening
SELECT pg_notify('test_channel', 'No listeners yet');

-- Right: First listen, then send
LISTEN test_channel;
SELECT pg_notify('test_channel', 'Now listeners will get this');

Quick Reference

Command	Description
LISTEN channel_name;	Start listening for notifications on the channel.
UNLISTEN channel_name;	Stop listening on the channel.
SELECT pg_notify(channel, payload);	Send a notification with optional payload.
NOTIFY channel, 'payload';	SQL command equivalent to pg_notify.

Key Takeaways

Use pg_notify(channel, payload) to send asynchronous notifications in PostgreSQL.

Always run LISTEN channel in a session to receive notifications on that channel.

Notifications are asynchronous; your application must handle them properly.

Channel names and payloads must be strings and have size limits.

Use UNLISTEN to stop receiving notifications when no longer needed.