Re: POC: Parallel processing of indexes in autovacuum

Hi,

On Wed, Apr 1, 2026 at 7:10 PM Alexander Korotkov <aekorotkov(at)gmail(dot)com> wrote:
>
> Thank you for your work on this subject! I've some notes about the patch.
>

Thank you very much for the review!

> 1) The changes in guc.c allows autovacuum parallel leader to accept
> changes in not just cost-based GUCs, but any GUCs. That should be no
> problem, because parallel workers have their own copies of GUC
> variables, but I think this worth comment.

OK, I will clarify it in the code.

> 2) Maximum value for autovacuum_parallel_workers reloption is defined
> as literally 1024, while max value for autovacuum_max_parallel_workers
> is defined as MAX_PARALLEL_WORKER_LIMIT (also 1024). Should we define
> max value for reloption as MAX_PARALLEL_WORKER_LIMIT as well?

I agree.

> 3) Some paragraphs were moved from vacuum.sgml to maintenance.sgml.
> It particular it references <replaceable
> class="parameter">integer</replaceable, which is related to PARALLEL
> option syntax: (PARALLEL integer). Now it becoming unclear and needs
> to be revised.

Good catch! You are right.

> 4) I also think maintenance.sgml should mention the new reloption.

Do you mean that we should mention it in the "parallel-vacuum" chapter? If so,
I think that we should also mention that max_parallel_maintenance_workers can
affect the parallel degree of manual VACUUM command. Yes, we have already
written about this in the description of the PARALLEL option. But now the
"vacuum-parallel" chapter doesn't mention limiting by GUC for manual VACUUM and
limiting by reloption for autovacuum. IMHO it is better to have redundancy than
an incomplete description.

> 5) I think it worth having a test which check that setting
> autovacuum_parallel_workers to 0 disables the parallel autovacuum for
> given table.

I see that VACUUM (PARALLEL) doesn't have such a test. Both manual VACUUM and
autovacuum have similar logic with parallelism disabling. Is the increase in
test completion time really worth checking these logic? I don't mind adding a
new test, actually. Just want to make sure that this is necessary.

> 6) Minor grammar issue in PVSharedCostParams comment, it must be
> "vacuum workers compare" (plural subject).

Yep, I'll fix it.

Please, see an updated patch.

--
Best regards,
Daniil Davydov