Re: Optimize LISTEN/NOTIFY

On Sep 28, 2025, at 18:24, Joel Jacobson <joel@compiler.org> wrote:

I might miss the factor of holding an exclusive lock. I will revisit 
that part again.

I've re-read this entire thread, and I actually think my original
approaches are more promising, that is, the
0001-optimize_listen_notify-v4.patch patch, doing multicast targeted
signaling.

Therefore, merely consider the latest patch as PoC with some possible
interesting ideas.

Before this patch, I had never used PostgreSQL's timeout mechanism
before, so I didn't consider it when thinking about how to solve the
remaining problems with 0001-optimize_listen_notify-v4.patch, which
currently can't guarantee that all listening backends will eventually
catch up, since it just kicks one of the most lagging ones, for each
notification. This could be a problem in practise if there is a long
period of time with no notifications coming in. Then some listening
backends could end up not being signaled and would stay behind,
preventing the queue tail from advancing.

I'm thinking maybe somehow we can use the timeout mechanism here, but
I'm not sure how yet. Any ideas?

/Joel