Re: SSI: ON CONFLICT DO SELECT takes no predicate lock on the returned row

From: Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>
To: Andrey Borodin <x4mmm(at)yandex-team(dot)ru>
Cc: Zsolt Parragi <zsolt(dot)parragi(at)percona(dot)com>, pgsql-hackers mailing list <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Nathan Bossart <nathandbossart(at)gmail(dot)com>
Subject: Re: SSI: ON CONFLICT DO SELECT takes no predicate lock on the returned row
Date: 2026-09-23 12:28:47
Message-ID: CAEZATCXiHxh-UZFj5QeStAjkoof+=DqYgaOvdQGE2DJt2nbQ_A@mail.gmail.com
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On Wed, 23 Sept 2026 at 12:22, Andrey Borodin <x4mmm(at)yandex-team(dot)ru> wrote:
>
> The snapshot change looks correct to me.

Hmm, I'm not so sure.

I'm thinking now that making ExecCheckIndexConstraints() require
estate->es_snapshot was actually an unintended change of the kind that
probably wasn't safe for back-patching, because it might affect
extension code.

Perhaps, instead, we should make it only do the re-fetch if
estate->es_snapshot is not InvalidSnapshot. For logical replication,
it actually seems unnecessary anyway, since it's only replaying an
update that has already been successfully committed by the publisher.

I wonder if it was actually intentional that logical replication
workers don't set es_snapshot on the EState, since they don't use it
to scan tables, so estate->es_snapshot is not needed.

Regards,
Dean

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