Message-ID: <d186fba0-dc65-4274-aa96-3906bbb2e530@postgrespro.ru>
Date: Tue, 2 Sep 2025 10:37:59 +0300
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Subject: Re: LISTEN/NOTIFY bug: VACUUM sets frozenxid past a xid in async
 queue
To: Matheus Alcantara <matheusssilv97@gmail.com>,
 Masahiko Sawada <sawada.mshk@gmail.com>
Cc: Daniil Davydov <3danissimo@gmail.com>,
 =?UTF-8?Q?=C3=81lvaro_Herrera?= <alvherre@kurilemu.de>,
 Alexandra Wang <alexandra.wang.oss@gmail.com>,
 PostgreSQL Hackers <pgsql-hackers@postgresql.org>
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From: Yura Sokolov <y.sokolov@postgrespro.ru>
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29.08.2025 01:31, Matheus Alcantara =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
> On Thu Aug 21, 2025 at 8:14 PM -03, Matheus Alcantara wrote:
>> I'll work on this considering the initial Daniil comments at [1]
>>
>> [1] https://www.postgresql.org/message-id/CAJDiXgg1ArRB1-6wLtXfVVnQ38P=
9Y%2BCDfEc9M2TXiOf_4kfBMg%40mail.gmail.com
>>
> I've been working on this on the last few days, please see the attached
> patch version.
>=20
> In this new version I tried to follow the suggestion from Daniil of
> scanning all pages from tail to head of the async queue.

Since we still need to scan those pages, couldn't we mark finished
transactions as committed/aborted?
This way we may to not hold datfrozenxid for a long time and will allow
both safe clog truncation and safe async queue notification.
More over, most notifications could be marked as completed in
AtCommit_Notify already. So there is a need to recheck a few notification=
s
that were written but not marked in AtCommit_Notify.

Since AsyncQueueEntry field is used only to check visibility, looks like =
it
is safe to set it to FrozenTransactionId.

--=20
regards
Yura Sokolov aka funny-falcon