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In-Reply-To: 
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From: Daniil Davydov <3danissimo@gmail.com>
Date: Fri, 3 Apr 2026 18:43:33 +0700
Message-ID: 
 <CAJDiXggr9FaaQ51PQK2Aurf5Y9+GAEZLCFRo6tUgVJ7aFavaXA@mail.gmail.com>
Subject: Re: POC: Parallel processing of indexes in autovacuum
To: Masahiko Sawada <sawada.mshk@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>
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 <https://www.postgresql.org/message-id/CAJDiXggr9FaaQ51PQK2Aurf5Y9%2BGAEZLCFRo6tUgVJ7aFavaXA%40mail.gmail.com>
Precedence: bulk

Hi,

On Fri, Apr 3, 2026 at 6:31=E2=80=AFAM Masahiko Sawada <sawada.mshk@gmail.c=
om> wrote:
>
> What do you think about the idea of using proc signals like the patch
> I've sent recently[1]? With that approach, workers have to check the
> local variable. It seems slightly cheaper and can use the existing
> logic.
>

Thank you for the patch!

1) Maybe we should implement this logic within ParallelMessages? For exampl=
e,
I see this ParallelMessages use case in parallel a/v :
/*
 * Call the parallel variant of pgstat_progress_incr_param so workers can
 * report progress of index vacuum to the leader.
 */
pgstat_progress_parallel_incr_param(PROGRESS_VACUUM_INDEXES_PROCESSED, 1);

I.e. parallel a/v workers already communicate with a leader via
ParallelMessages, so it will be convenient to extend this protocol by a new
message.

2) I don't think that the difference between accessing atomic and local
variable can be measured for parallel workers. But sending a signal to ever=
y
parallel worker is surely slower than just incrementing an atomic variable.
IIUC you created this patch in order to solve the task of using an existing
infrastructure instead of creating a new utilitarian solution. However, I t=
hink
that both the polling approach and signalling approach (in its current
implementation) are basically equal. I mean that in both cases we have an
autovacuum-specific mechanism to share particular parameters between partic=
ular
workers.

I will try to explain how I see the solution to this problem. :
Your implementation can be made more abstract, so that it becomes a new
internal mechanism that other modules can use in the future. E.g. we can cr=
eate
an interface that allows any parallel leader (not necessarily just an
autovacuum leader) to inform its parallel workers that some config paramete=
rs
have been changed. At the same time, parallel workers can use this interfac=
e in
order to specify, which parameters (or groups of parameters) they want to
consume from the leader. What do you think?

--
Best regards,
Daniil Davydov