[bgentry]

This is largely because LISTEN/NOTIFY has an implementation which uses a global lock. At high volume this obviously breaks down: https://www.recall.ai/blog/postgres-listen-notify-does-not-s...

None of that means Oban or similar queues don't/can't scale—it just means a high volume of NOTIFY doesn't scale, hence the alternative notifiers and the fact that most of its job processing doesn't depend on notifications at all.

There are other reasons Oban recommends a different notifier per the doc link above:

> That keeps notifications out of the db, reduces total queries, and allows larger messages, with the tradeoff that notifications from within a database transaction may be sent even if the transaction is rolled back

[parthdesai]

> None of that means Oban or similar queues don't/can't scale—it just means a high volume of NOTIFY doesn't scale

Given the context of this post, it really does mean the same thing though?

[bgentry]

No, I don't think so. Oban does not rely on a large volume of NOTIFY in order to process a large volume of jobs. The insert notifications are simply a latency optimization for lower volume environments, and for inserts can be fully disabled such that they're mainly used for control flow (canceling jobs, pausing queues, etc) and gossip among workers.

River for example also uses LISTEN/NOTIFY for some stuff, but we definitely do not emit a NOTIFY for every single job that's inserted; instead there's a debouncing setup where each client notifies at most once per fetch period, and you don't need notifications at all in order to process with extremely high throughput.

In short, the fact that high volume NOTIFY is a bottleneck does not mean these systems cannot scale, because they do not rely on a high volume of NOTIFY or even require it at all.

[victorbjorklund]

Yup. I wasn’t talking about notify in particular but about using Postgres in general.