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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: "Imseih (AWS), Sami" <simseih@amazon.com>
Cc: "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2024-04-13T19:44:50Z
Lists: pgsql-hackers 
On Fri, Apr 12, 2024 at 10:17:44PM +0000, Imseih (AWS), Sami wrote:
>>> Hm. Maybe the autovacuum launcher could do that.
> 
> Would it be better to use a GUC check_hook that compares the 
> new value with the max allowed values and emits a WARNING ?
> 
> autovacuum_max_workers already has a check_autovacuum_max_workers
> check_hook, which can be repurposed for this.
> 
> In the POC patch, this check_hook is kept as-is, which will no longer make sense.

IIRC using GUC hooks to handle dependencies like this is generally frowned
upon because it tends to not work very well [0].  We could probably get it
to work for this particular case, but IMHO we should still try to avoid
this approach.  I didn't find any similar warnings for other GUCs like
max_parallel_workers_per_gather, so it might not be crucial to emit a
WARNING here.

[0] https://postgr.es/m/27574.1581015893%40sss.pgh.pa.us

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com

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.