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From: Matheus Alcantara <matheusssilv97@gmail.com>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: Daniil Davydov <3danissimo@gmail.com>
Cc: Álvaro Herrera <alvherre@kurilemu.de>
Cc: Alexandra Wang <alexandra.wang.oss@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Subject: Re: LISTEN/NOTIFY bug: VACUUM sets frozenxid past a xid in async queue
Date: Thu, 21 Aug 2025 20:14:47 -0300
Message-ID: <DC8HKDZVIDYG.12H0X267CHMO5@gmail.com> (raw)
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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%2BCDfEc9M2TXiOf_4kfBMg%40mail.g...

--
Matheus Alcantara






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  Cc: matheusssilv97@gmail.com, sawada.mshk@gmail.com, 3danissimo@gmail.com, alvherre@kurilemu.de, alexandra.wang.oss@gmail.com
  Subject: Re: LISTEN/NOTIFY bug: VACUUM sets frozenxid past a xid in async queue
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