NOTIFY(7)

💌 NOTIFY(7) — the "hey bestie, something happened" of PostgreSQL ✨

Okay so picture this: you're deep in your PostgreSQL era and you need one part of your database to tell another part that something changed. That's literally what NOTIFY is for, and honestly? It's giving interprocess communication but make it cute. 🎀

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🌸 NAME

NOTIFY — generate a notification

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🦋 SYNOPSIS

NOTIFY channel [ , payload ]

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✨ DESCRIPTION

So here's the tea: the NOTIFY command sends a notification event — plus an optional "payload" string — to every client application that has already run LISTEN channel for that specific channel name in the current database. And not me explaining it like it's some exclusive club, because notifications are visible to all users. Periodt. 💅

NOTIFY is basically the low-key interprocess communication mechanism for a whole crew of processes all accessing the same PostgreSQL database. You can slide a payload string along with the notification, and if you need to pass structured data, you can level up by using tables in the database to pass extra data from the notifier to the listener(s). Highkey genius. 🧚

When a notification event gets passed to the client, it includes the notification channel name, the notifying session's server process PID, and the payload string. And if you didn't specify a payload? It's just an empty string. No cap, that's the default. 🙈

Now, it's up to the database designer to define the channel names that will be used in a given database and what each one means. Usually, the channel name is the same as the name of some table in the database, and the notify event essentially means, "I changed this table, take a look at it to see what's new." But — and this is important — no such association is enforced by the NOTIFY and LISTEN commands. For example, a database designer could use several different channel names to signal different sorts of changes to a single table. Or, alternatively, the payload string could be used to differentiate various cases. It's giving flexible and iconic. 🌈

When NOTIFY is used to signal the occurrence of changes to a particular table, a useful programming technique is to put the NOTIFY in a statement trigger that is triggered by table updates. In this way, notification happens automatically when the table is changed, and the application programmer cannot accidentally forget to do it. Obsessed with the no-forgetting energy. 🔥

NOTIFY interacts with SQL transactions in some important ways, and bestie, you need to know this:

• Firstly, if a NOTIFY is executed inside a transaction, the notify events are not delivered until and unless the transaction is committed. This is appropriate, since if the transaction is aborted, all the commands within it have had no effect, including NOTIFY. But it can be disconcerting if you're expecting the notification events to be delivered immediately. Fair, honestly. 😭
• Secondly, if a listening session receives a notification signal while it is within a transaction, the notification event will not be delivered to its connected client until just after the transaction is completed (either committed or aborted). Again, the reasoning is that if a notification were delivered within a transaction that was later aborted, one would want the notification to be undone somehow — but the server cannot "take back" a notification once it has sent it to the client. So notification events are only delivered between transactions. The upshot? Applications using NOTIFY for real-time signaling should try to keep their transactions short. Short and slay. ⭐

If the same channel name is signaled multiple times with identical payload strings within the same transaction, only one instance of the notification event is delivered to listeners. On the other hand, notifications with distinct payload strings will always be delivered as distinct notifications. Similarly, notifications from different transactions will never get folded into one notification. Except for dropping later instances of duplicate notifications, NOTIFY guarantees that notifications from the same transaction get delivered in the order they were sent. It's also guaranteed that messages from different transactions are delivered in the order in which the transactions committed. So the vibes are ordered, and that's on periodt. 👑

It is common for a client that executes NOTIFY to be listening on the same notification channel itself. In that case it will get back a notification event, just like all the other listening sessions. Depending on the application logic, this could result in useless work — for example, reading a database table to find the same updates that that session just wrote out. It is possible to avoid such extra work by noticing whether the notifying session's server process PID (supplied in the notification event message) is the same as one's own session's PID (available from libpq). When they are the same, the notification event is one's own work bouncing back, and can be ignored. Main character energy: check the PID, ignore yourself. 💀

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💖 PARAMETERS

• channel — Name of the notification channel to be signaled (any identifier). You pick it, you own it. 🎀
• payload — The "payload" string to be communicated along with the notification. This must be specified as a simple string literal. In the default configuration it must be shorter than 8000 bytes. (If binary data or large amounts of information need to be communicated, it's best to put it in a database table and send the key of the record. Just saying. 🍓)

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🫶 NOTES

There is a queue that holds notifications that have been sent but not yet processed by all listening sessions. If this queue becomes full, transactions calling NOTIFY will fail at commit. The queue is quite large — 8GB in a standard installation — and should be sufficiently sized for almost every use case. However, no cleanup can take place if a session executes LISTEN and then enters a transaction for a very long time. Once the queue is half full you will see warnings in the log file pointing you to the session that is preventing cleanup. In this case you should make sure that this session ends its current transaction so that cleanup can proceed. Don't be the session blocking the queue, bestie. 🙈

The function pg_notification_queue_usage returns the fraction of the queue that is currently occupied by pending notifications. See Section 9.26 for more information. 📚

A transaction that has executed NOTIFY cannot be prepared for two-phase commit. That's just the rules. 💅

🧚 pg_notify

To send a notification you can also use the function pg_notify(text, text). The function takes the channel name as the first argument and the payload as the second. The function is much easier to use than the NOTIFY command if you need to work with non-constant channel names and payloads. Literally easier. Use it. ⭐

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🌟 EXAMPLES

Configure and execute a listen/notify sequence from psql:

LISTEN virtual;
NOTIFY virtual;
Asynchronous notification "virtual" received from server process with PID 8448.
NOTIFY virtual, 'This is the payload';
Asynchronous notification "virtual" with payload "This is the payload" received from server process with PID 8448.

LISTEN foo;
SELECT pg_notify('fo' || 'o', 'pay' || 'load');
Asynchronous notification "foo" with payload "payload" received from server process with PID 14728.

Look at that. Beautiful. The payload is literally "This is the payload" and it still ate. 🔥

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🎀 COMPATIBILITY

There is no NOTIFY statement in the SQL standard. We're built different. 💅

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💜 SEE ALSO

LISTEN(7), UNLISTEN(7)

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PostgreSQL 15.19, dated 2026, page NOTIFY(7) — that's the whole vibe. Byeee bestie, go notify someone! 👑🦋💖