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Postgres LISTEN/NOTIFY does not scale

(www.recall.ai)
570 points davidgu | 1 comments | 07 Jul 25 14:05 UTC | HN request time: 0.215s | source
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leontrolski ◴[10 Jul 25 21:00 UTC] No.44525560[source]▶
I'd be interested as to how dumb-ol' polling would compare here (the FOR UPDATE SKIP LOCKED method https://leontrolski.github.io/postgres-as-queue.html). One day I will set up some benchmarks as this is the kind of thing people argue about a lot without much evidence either way.

Wasn't aware of this AccessExclusiveLock behaviour - a reminder (and shameless plug 2) of how Postgres locks interact: https://leontrolski.github.io/pglockpy.html

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1. sorentwo ◴[11 Jul 25 02:06 UTC] No.44527778[source]▶
Ping requires something persistent to check. That requires creating tuples, and most likely deleting them after they’ve been consumed. That puts pressure on the database and requires vacuuming in ways that pubsub doesn’t because it’s entirely ephemeral.

Not to mention that pubsub allows multiple consumers for a single message, whereas FOR UPDATE is single consumer by design.