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In-Reply-To: 
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From: Daniil Davydov <3danissimo@gmail.com>
Date: Tue, 31 Mar 2026 21:18:34 +0700
Message-ID: 
 <CAJDiXgj3A=wNC-S0z3TixmnVUkifs=07yLLHJ7_+dDsakft1tA@mail.gmail.com>
Subject: Re: POC: Parallel processing of indexes in autovacuum
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com>,
	Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>,
 Sami Imseih <samimseih@gmail.com>,
	Alexander Korotkov <aekorotkov@gmail.com>,
 Matheus Alcantara <matheusssilv97@gmail.com>,
	Maxim Orlov <orlovmg@gmail.com>,
 Postgres hackers <pgsql-hackers@lists.postgresql.org>
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 <https://www.postgresql.org/message-id/CAJDiXgj3A%3DwNC-S0z3TixmnVUkifs%3D07yLLHJ7_%2BdDsakft1tA%40mail.gmail.com>
Precedence: bulk

Hi,

On Tue, Mar 31, 2026 at 2:09=E2=80=AFPM Masahiko Sawada <sawada.mshk@gmail.=
com> wrote:
>
> I've made some changes to the documentation part, merged two patches
> into one, and updated the commit message. Please review the attached
> patch.
>

Great, thank you very much!

Again, I don't know how to write the documentation well, so you can ignore
my comments :

> +    <command>VACUUM</command> can perform index vacuuming and index clea=
nup
Don't we need to mention autovacuum here too? I thought that VACUUM in the
context means "manual VACUUM command".

> + ...applies specifically to the index vacuuming and index cleanup phases=
...
Maybe we can refer to "vacuum-phases" here?

All other changes look good to me.

!!!
> Searching for arguments in
> favor of opt-in style, I asked for help from another person who has been
> managing the setup of highload systems for decades. He promised to share =
his
> opinion next week.

I talked to Anton Doroshkevich today.
He confirmed that as a rule there are *hundreds of thousands* of tables in =
the
system, the vast majority of which do not need to be vacuumed in parallel m=
ode.

He also suggested the following : let the reloption overlap the value of th=
e
GUC parameter. I.e. even if av_max_parallel_workers parameters is 0 the use=
r
still can set the av_parallel_workers to 10 for some table, and autovacuum
will process this table in parallel.

I remember that you want to use the GUC parameter as a global switch, and t=
his
approach will break this logic. But according to Anton's words, it is okay =
if
the GUC parameter cannot disable parallel a/v for all tables instantly. It =
will
become an administrator's responsibility to manually turn off parallel a/v =
for
several tables (again, it is completely OK). Thus, this feature can be hand=
y
for all use cases.

I hope it doesn't look like as an adapting to the needs of a specific user.
A lot of super-large productions are migrating to postgres now, and I belie=
ve
that we should ensure their comfort too.

What do you think? Can postgres have such a logic?

--
Best regards,
Daniil Davydov