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In-Reply-To: 
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From: Amit Kapila <amit.kapila16@gmail.com>
Date: Tue, 26 Aug 2025 16:38:17 +0530
Message-ID: 
 <CAA4eK1+7bNcjF5gRnfACgLMq1VPKQdD8fR43Rd93wdMzLqCbdA@mail.gmail.com>
Subject: Re: [BUG?] check_exclusion_or_unique_constraint false negative
To: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
Cc: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>,
 Peter Geoghegan <pg@bowt.ie>,
	"Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>,
	PostgreSQL Hackers <pgsql-hackers@postgresql.org>,
 Andres Freund <andres@anarazel.de>
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Precedence: bulk

On Mon, Aug 25, 2025 at 7:02=E2=80=AFPM Mihail Nikalayeu
<mihailnikalayeu@gmail.com> wrote:
>
> Amit Kapila <amit.kapila16@gmail.com>:
>
>
> > What if the new insert happens in a page prior to the current page? I
> > mean that the scan won't encounter the page where Insert happens.
>
> Hmm.... Yes - if the TID lands to the page left of the current
> position, we=E2=80=99ll miss it as well.
> A lock=E2=80=91based solution (version in the v10) would require keeping =
all
> pages with the same key under a read lock, which feels too expensive.
>

Right.

> > BTW, do we know the reason behind using SnapshotDirty in the first
> > place? I don't see any comments in the nearby code unless I am missing
> > something.
>
> I think this is simply an attempt to lock the newest version of the
> logical tuple, including INSERT cases.
> For an existing tuple, the same can be achieved using MVCC snapshot + ret=
ry.
> However, in the case of a not-yet-committed INSERT, a different type
> of snapshot is required.
>
> But I'm not sure if it provides any advantages.
>

I think it is better to document this race somewhere in a logical
replication document for now unless we have a consensus on a way to
move forward.

--=20
With Regards,
Amit Kapila.