Re: Optimize LISTEN/NOTIFY

Tom Lane <tgl@sss.pgh.pa.us>

From: Tom Lane <tgl@sss.pgh.pa.us>

To: "Joel Jacobson" <joel@compiler.org>

Cc: pgsql-hackers <pgsql-hackers@postgresql.org>

Date: 2025-07-12T23:18:40Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

Optimize LISTEN/NOTIFY via shared channel map and direct advancement.
- 282b1cde9ded 19 (unreleased) landed
Fix incorrect logic for caching ResultRelInfos for triggers
- 39dcfda2d23a 19 (unreleased) cited

"Joel Jacobson" <joel@compiler.org> writes:
> The attached proof-of-concept patch proposes a straightforward
> optimization for the single-listener case. It introduces a shared-memory
> hash table mapping (dboid, channelname) to the ProcNumber of a single
> listener.

What does that do to the cost and parallelizability of LISTEN/UNLISTEN?

> The patch also includes a "wake only tail" optimization (contributed by
> Marko Tikkaja) to help prevent backends from falling too far behind.

Coulda sworn we dealt with that case some years ago.  In any case,
if it's independent of the other idea it should probably get its
own thread.

			regards, tom lane