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In-Reply-To: 
 <CAJDiXgjctmV-vLSjSQFxkANT-VZzwjJCmYGcJQ_y3+TkjxcrWg@mail.gmail.com>
From: Masahiko Sawada <sawada.mshk@gmail.com>
Date: Wed, 1 Apr 2026 16:15:33 -0700
Message-ID: 
 <CAD21AoAm806fQhMH49T_Ft9z1HSAdTi=gRcoxS9DW+nVQ9iCMQ@mail.gmail.com>
Subject: Re: POC: Parallel processing of indexes in autovacuum
To: Daniil Davydov <3danissimo@gmail.com>
Cc: Alexander Korotkov <aekorotkov@gmail.com>,
	SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com>,
	Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>,
 Sami Imseih <samimseih@gmail.com>,
	Matheus Alcantara <matheusssilv97@gmail.com>,
 Maxim Orlov <orlovmg@gmail.com>,
	Postgres hackers <pgsql-hackers@lists.postgresql.org>
Content-Type: text/plain; charset="UTF-8"
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Archived-At: 
 <https://www.postgresql.org/message-id/CAD21AoAm806fQhMH49T_Ft9z1HSAdTi%3DgRcoxS9DW%2BnVQ9iCMQ%40mail.gmail.com>
Precedence: bulk

On Wed, Apr 1, 2026 at 2:24=E2=80=AFPM Daniil Davydov <3danissimo@gmail.com=
> wrote:
>
> Hi,
>
> On Wed, Apr 1, 2026 at 7:10=E2=80=AFPM Alexander Korotkov <aekorotkov@gma=
il.com> wrote:
> >
> > Thank you for your work on this subject!  I've some notes about the pat=
ch.
> >
>
> 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=3D"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? I=
f 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 VACU=
UM and
> limiting by reloption for autovacuum. IMHO it is better to have redundanc=
y 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 addi=
ng 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.

Thank you for updating the patch! I found a bug in the following code:

@@ -457,6 +534,9 @@ parallel_vacuum_end(ParallelVacuumState *pvs,
IndexBulkDeleteResult **istats)
  DestroyParallelContext(pvs->pcxt);
  ExitParallelMode();

+ if (AmAutoVacuumWorkerProcess())
+ pv_shared_cost_params =3D NULL;
+

If an autovacuum worker raises an error during parallel vacuum, it
doesn't pv_shared_cost_params. Then, if it doesn't use parallel vacuum
on the next table to vacuum, it would end up with SEGV as it attempts
to propagate the vacuum delay parameters.

Regards,

--=20
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com