Re: allow changing autovacuum_max_workers without restarting

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