How to Use NOTIFY in PostgreSQL for Event Notifications

In PostgreSQL, use the NOTIFY command to send a notification event with a channel name and optional payload. Other sessions can listen for these events using LISTEN, enabling asynchronous communication between database clients.

Syntax

The NOTIFY command sends a notification to all clients listening on a specified channel. It has this form:

• NOTIFY channel; — sends a notification without a payload.
• NOTIFY channel, 'payload'; — sends a notification with a text payload.

The channel is a name identifying the notification topic, and the optional payload is a string message.

sql

NOTIFY channel_name;
NOTIFY channel_name, 'your message here';

Example

This example shows how one session sends a notification and another session listens for it.

First, start listening on a channel:

sql

-- Session 1: Listen for notifications
LISTEN my_channel;

-- Session 2: Send a notification
NOTIFY my_channel, 'Hello listeners!';

Output

LISTEN
NOTIFY

Common Pitfalls

• For NOTIFY to work, the listening session must have executed LISTEN on the same channel beforehand.
• Notifications are asynchronous; the sender does not wait for receivers to process the message.
• Payloads are limited to 8000 bytes; larger messages will be truncated.
• Notifications are not persistent; if no session is listening, the notification is lost.

sql

/* Wrong: Sending notification without listener active */
NOTIFY my_channel, 'Test message';

/* Right: First listen, then notify */
-- In one session:
LISTEN my_channel;
-- In another session:
NOTIFY my_channel, 'Test message';

Quick Reference

Command	Description
LISTEN channel_name;	Start listening for notifications on a channel
NOTIFY channel_name;	Send a notification without payload
NOTIFY channel_name, 'payload';	Send a notification with a text payload
UNLISTEN channel_name;	Stop listening on a specific channel
UNLISTEN *;	Stop listening on all channels

Key Takeaways

Use LISTEN to subscribe to a notification channel before sending NOTIFY.

NOTIFY sends asynchronous messages that listeners can react to in real time.

Payloads in NOTIFY are optional and limited in size to 8000 bytes.

Notifications are lost if no session is listening on the channel.

Use UNLISTEN to stop receiving notifications when no longer needed.