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From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: Kirill Reshke <reshkekirill@gmail.com>
Cc: pgsql-hackers@lists.postgresql.org, Amit Kapila <amit.kapila16@gmail.com>
Subject: Re: Report relation extension blockers within parallel lock groups
Date: Tue, 22 Sep 2026 05:04:34 +0000
Message-ID: <arIMYhZyTImZ6fLt@bdtpg> (raw)
In-Reply-To: <CALdSSPgOpyJiDorxA9bNvwT04xAeJ_CJH3AWXpmckJ1ttzBNcQ@mail.gmail.com>
References: <apTpV8h+CYHf+1PJ@bdtpg>
	<CALdSSPgOpyJiDorxA9bNvwT04xAeJ_CJH3AWXpmckJ1ttzBNcQ@mail.gmail.com>

Hi,

On Fri, Sep 04, 2026 at 10:45:11AM +0500, Kirill Reshke wrote:
> On Mon, 31 Aug 2026 at 07:39, Bertrand Drouvot
> <bertranddrouvot.pg@gmail.com> wrote:
> >
> > Hi hackers,
> >
> > While working on providing more informations related to locks (patch not shared
> > yet), it appeared that pg_blocking_pids() can omit the process that is actually
> > blocking a relation extension request.
> >
> > Indeed, commit 85f6b49c2c53 made relation extension locks conflict between members
> > of the same parallel lock group, but did not update the same group filtering in
> > pg_blocking_pids().
> >
> > The attached adds the relation extension exception in pg_blocking_pids().
> >
> > pg_blocking_pids() reports parallel workers using their lock group leader PID.
> > Therefore, when one member of a parallel lock group blocks another, the PID
> > supplied to pg_blocking_pids() can appear in the result. This does not mean
> > that a process blocks itself. Rather, a lock held by one member of its parallel
> > lock group blocks a lock request made by another member of that group. The patch
> > documents this behavior.
> 
> 
> Your fix looks correct to me, matches deadlock detector code.

Thanks for looking at it!

> > No regression test is added because ensuring relation extension lock contention
> > between members of the same parallel lock group would be more complicated than
> > needed for this simple patch.
> 
> Isolation test you mean? Shouldn't be that hard using injection
> points, but Anyway, I think I agree, too much cpu cycles will be
> wasted on this small issue.

Yeah, that does not seem worth it.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com

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