[diek]

In a large application you may have dozens of tables that different backends may be operating on. Each worker pool polling on tables it may be interested on every couple seconds can add up, and it's really not necessary.

Another factor is polling frequency and processing latency. All things equal, the delay from when a new task lands in a table to the time a backend is working on it should be as small as possible. Single digit milliseconds, ideally.

A NOTIFY event is sent from the server-side as the transaction commits, and you can have a thread blocking waiting on that message to process it as soon as it arrives on the worker side.

So with NOTIFY you reduce polling load and also reduce latency. The only time you need to actually query for tasks is to take over any expired leases, and since there is a 'lease_expire' column you know when that's going to happen so you don't have to continually check in.

As far as documentation, I got a simple java LISTEN/NOTIFY implementation working initially (2013?-ish) just from the excellent postgres docs: https://www.postgresql.org/docs/current/sql-notify.html