Mime-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain; charset=UTF-8
Date: Thu, 21 Aug 2025 20:14:47 -0300
Message-Id: <DC8HKDZVIDYG.12H0X267CHMO5@gmail.com>
Subject: Re: LISTEN/NOTIFY bug: VACUUM sets frozenxid past a xid in async
 queue
From: "Matheus Alcantara" <matheusssilv97@gmail.com>
To: "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>
References: 
 <CAK98qZ3wZLE-RZJN_Y+TFjiTRPPFPBwNBpBi5K5CU8hUHkzDpw@mail.gmail.com>
 <202508061044.ptcyt7aqsaaa@alvherre.pgsql>
 <DBZN3PVLZ1UW.25XLKCUXYBVXV@gmail.com>
 <CAJDiXgg1ArRB1-6wLtXfVVnQ38P9Y+CDfEc9M2TXiOf_4kfBMg@mail.gmail.com>
 <CAFY6G8cnDOMZCfSvc62vER_9+HOs4EM52XromhOZki+=Ytv2sg@mail.gmail.com>
 <CAJDiXgheRHTnK8RJuBBcF0VjQA83wi81oX2s-GvBV3x+eSwBbA@mail.gmail.com>
 <CAFY6G8dyimRikP3nEK5gqMPnMZe5RTZjFvKvCFLJAvsajxK1fg@mail.gmail.com>
 <CAJDiXgjQZgHLFziG6sS6D5CGYqohMio673ydiRkkffW3WfXmEg@mail.gmail.com>
 <DC7KGTXW3QSG.OZA24HONT78J@gmail.com>
 <CAD21AoCD+HXoc2QZCAS9d8ahDeikNqbnU0i6cQzpMFOEurkPPg@mail.gmail.com>
In-Reply-To: 
 <CAD21AoCD+HXoc2QZCAS9d8ahDeikNqbnU0i6cQzpMFOEurkPPg@mail.gmail.com>
Archived-At: 
 <https://www.postgresql.org/message-id/DC8HKDZVIDYG.12H0X267CHMO5%40gmail.com>
Precedence: bulk

On Thu Aug 21, 2025 at 7:25 PM -03, Masahiko Sawada wrote:
> What about backend processes that don't have any xid or xmin (i.e.,
> are read-only query and in idle-in-transaction)?
>
> IIUC we process the notification entries at the beginning of the
> server loop (see L4608 in postgres.c) and when reading a command (via
> ProcessClientReadInterrupt()), but it seems to me that if a process is
> in idle-in-transaction state it doesn't process the entries unless the
> transaction is committed. I've reproduced the missing clog entry error
> even if we have a notification on the queue with a valid listener,
> with the following steps:
>
Ok, now we can reproduce this, thank you! So I think that we need a way
to teach the VACUUM FREEZE about old xid's on async queue.

I'll work on this considering the initial Daniil comments at [1]

[1] https://www.postgresql.org/message-id/CAJDiXgg1ArRB1-6wLtXfVVnQ38P9Y%2B=
CDfEc9M2TXiOf_4kfBMg%40mail.gmail.com

--
Matheus Alcantara