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Re: allow changing autovacuum_max_workers without restarting

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Peter Eisentraut <peter@eisentraut.org>, Andres Freund <andres@anarazel.de>, pgsql-hackers@lists.postgresql.org, "Imseih (AWS), Sami" <simseih@amazon.com>, Justin Pryzby <pryzby@telsasoft.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2025-04-29T17:42:19Z
Lists: pgsql-hackers 
On Tue, Apr 29, 2025 at 01:31:55PM -0400, Tom Lane wrote:
> I wrote:
>> Andres seemed lukewarm about reverting 38da05346 or 6d0154196, so
>> I left it be for the moment.  But I still feel the argument is good
>> that "these will do little except confuse future hackers".  Barring
>> objection, I'll go revert them.
> 
> Actually ... on looking again at 6d0154196 ("Lower default value of
> autovacuum_worker_slots in initdb as needed"), it doesn't look that
> silly.  If we're unable to allocate max_connections = 100, turning
> it down while still insisting on 16 AV worker slots doesn't seem
> terribly sane.  Maybe we'd choose a formula other than
> "(max_connections / 6)" if we were doing it afresh, but not scaling
> autovacuum_worker_slots at all doesn't seem like the best answer.

Fair point.

> So now I'm inclined to leave that one alone.  I'd still revert
> 38da05346, which means the comment added by 6d0154196 needs some minor
> adjustments.  But I think we can stick with the "(max_connections /
> 6)" formula --- it will produce 3 with trial_conns = 20, but that's
> enough.

Yup, as long as the lowest possible default is >= the default for
autovacuum_max_workers (3), we're good.

-- 
nathan

Commits

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

  1. Give up on running with NetBSD/OpenBSD's default semaphore settings.

  2. initdb: Do not report default autovacuum_worker_slots.

  3. Lower default value of autovacuum_worker_slots in initdb as needed.

  4. Allow changing autovacuum_max_workers without restarting.

  5. Reserve a PGPROC slot and semaphore for the slotsync worker process.

  6. Make archiver process an auxiliary process.

  7. Correct the formulas for System V IPC parameters SEMMNI and SEMMNS in docs.