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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: 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: 2025-01-07T17:23:47Z
Lists: pgsql-hackers

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On Mon, Jan 06, 2025 at 10:29:07PM -0500, Tom Lane wrote:
> +1 for simplicity ... but on reflection, what do you think about
> using max_connections / 6?  That would keep autovacuum_worker_slots
> at 100 / 6 = 16 for the vast majority of systems.  For the worst case
> *BSD machines, we'd select 25 / 6 = 4 which results in consuming one
> more semaphore than where we were yesterday.  I'm willing to accept
> that outcome though, since we still have 3 or so to spare.

WFM.  I'm kicking myself for not having thought of that...

> Other than the specific magic number, your patch LGTM.

Here's a new version of the patch with some small cosmetic changes
(including more commentary about the formula) and the constant changed to
6.  I'll go commit this shortly.

-- 
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.