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In-Reply-To: 
 <CAHg+QDdfsS6DQMUNQUW9ZDt_D0FtfygabkeAkRY5Yy2SeeNbLA@mail.gmail.com>
From: Daniil Davydov <3danissimo@gmail.com>
Date: Tue, 31 Mar 2026 20:26:29 +0700
Message-ID: 
 <CAJDiXgjcAfJnu-w49WrKYAtj6h0gos7YmttBf=M++=52kQE_9A@mail.gmail.com>
Subject: Re: POC: Parallel processing of indexes in autovacuum
To: SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com>
Cc: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>,
	Masahiko Sawada <sawada.mshk@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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Archived-At: 
 <https://www.postgresql.org/message-id/CAJDiXgjcAfJnu-w49WrKYAtj6h0gos7YmttBf%3DM%2B%2B%3D52kQE_9A%40mail.gmail.com>
Precedence: bulk

Hi,

On Tue, Mar 31, 2026 at 2:46=E2=80=AFPM SATYANARAYANA NARLAPURAM
<satyanarlapuram@gmail.com> wrote:
>
> On Mon, Mar 30, 2026 at 1:44=E2=80=AFAM Daniil Davydov <3danissimo@gmail.=
com> wrote:
>>
>> Actually, autovacuum_max_parallel_workers is already limited by
>> max_parallel_workers. It is not clear for me why we allow setting this G=
UC
>> higher than max_parallel_workers, but if this happens, I think it is a u=
ser's
>> misconfiguration.
>
> Isn=E2=80=99t there a wasted effort here if user misconfigures because an=
yway we cannot launch that many workers? I suggest making a check here.

We have a pretty long discussion about this in the above messages. I also
think that the user have too many ways to misconfigure postgres. But we
don't consider such misconfiguration as our fault.

>> Parallel a/v workers inherit cost based parameters (including the
>> vacuum_cost_limit) from the leader worker. Do you mean that this can be =
too
>> low value for parallel operation? If so, user can manually increase the
>> vacuum_cost_limit reloption for those tables, where parallel a/v sleeps =
too
>> much (due to cost delay).
>
>
> They don=E2=80=99t inherit but share, isn=E2=80=99t it?
>

Yeah, let me clarify. At the beginning of parallel a/v, the leader a/v work=
er
creates and initializes a shared structure, where its cost based parameters
are stored. Then, all parallel workers will read them from shmem and update
their parameters accordingly.

--
Best regards,
Daniil Davydov