The Notifier Pattern for Applications That Use Postgres

Listen/notify in Postgres is an incredible feature that makes itself useful in all kinds of situations. I’ve been using it a long time, started taking it for granted long ago, and was somewhat shocked recently looking into MySQL and SQLite to learn that even in 2024, no equivalent exists.

In a basic sense, listen/notify is such a simple concept that it needs little explanation. Clients subscribe on topics and other clients can send on topics, passing a message to each subscribed client. The idea takes only three seconds to demonstrate using nothing more than a psql shell:

But despite listen/notify’s relative simplicity, when it comes to applications built on top of Postgres, it’s common to use it less than optimally, eating through scarce Postgres connections and with little regard to failure cases.

Here’s where the notifier pattern for Postgres comes in. It’s an extremely simple idea, but in my experience, one that’s rarely seen in practice. Let’s start with these axioms:

Leave a Comment