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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: 2025-01-06T23:20:22Z
Lists: pgsql-hackers

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On Mon, Jan 06, 2025 at 05:36:17PM -0500, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
>> How about trying the higher setting first in initdb? On any sane system
>> that won't cost anything because it'll succeed with the higher value.
> 
> That might be a good compromise.

+1, I like the idea.

> You'd have to think about how
> it should interact with initdb's probes for workable values of
> max_connections.  My first thought about that is to have initdb
> set autovacuum_worker_slots to max_connections / 8 or thereabouts
> as it works down the list of max_connections values to try.  Or
> you could do something more complicated, but I don't see a reason
> to make it too complex.

My first instinct was just to set it to the lowest default we'd consider
during the max_connections tests (which I'm assuming is 3 due to the
current default for autovacuum_max_workers).  That way, the max_connections
default won't change from version to version on affected systems, but you
might get some extra autovacuum slots.

-- 
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.