From: Japin Li <japinli@hotmail.com>
To: wenhui qiu <qiuwenhuifx@gmail.com>
Cc: Shinya Kato <shinya11.kato@gmail.com>,  Scott Ray <scott@scottray.io>,
  Kyotaro Horiguchi <horikyota.ntt@gmail.com>,  laurenz.albe@cybertec.at,
  samimseih@gmail.com,  pgsql-hackers@lists.postgresql.org
Subject: Re: Report oldest xmin source when autovacuum cannot remove tuples
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	(wenhui qiu's message of "Wed, 3 Jun 2026 10:32:07 +0800")
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Precedence: bulk

On Wed, 03 Jun 2026 at 10:32, wenhui qiu <qiuwenhuifx@gmail.com> wrote:
> HI Shinya
>> I agree that exposing xid horizon retention information via a
>> SQL-visible interface is valuable. However, I believe reporting it
>> in the VACUUM log is also important: a view only shows the current
>> state, so once a blocker has gone away there is no way to determine,
>> after the fact, what was holding the horizon back at the time a
>> particular VACUUM ran. Logs are the only durable record we have for
>> that kind of post-hoc analysis.
> Agree +1,There's no denying that checking SQL is easier than checking log=
s. Logs are also important though. In fact, I
> think we should apply this patch first and implement the SQL later.
>

+1 for this idea.  I don't think they conflict with each other =E2=80=94 th=
ey just
provide the same content from different perspectives.

> Thanks
>
> On Wed, Jun 3, 2026 at 9:25=E2=80=AFAM Shinya Kato <shinya11.kato@gmail.c=
om> wrote:
>
>  On Wed, Jun 3, 2026 at 10:05=E2=80=AFAM Scott Ray <scott@scottray.io> wr=
ote:
>  > I've been working on a view like this.  It shows the horizon
>  > contribution for each backend, prepared xact, replication slot, and
>  > HSF walsender, broken down by class.  It also shows - for each
>  > contributor - how the horizon would shift if that holder were
>  > removed.
>  >
>  > Shinya said [1] that we could have a view in the future.  We could
>  > have both the logging and the view call a single function that reads
>  > the procArray and other sources to gather the horizon information.  I
>  > think the logging and the view would complement each other.
>  >
>  > Should I start another thread?
>
>  My mild preference would be to keep the discussion on this thread,
>  since the shared function design is central to both the log and the
>  view and may be easier to keep aligned in one place. That said, I'm
>  not strongly attached to that, so please pick whichever feels more
>  convenient.
>
>  --=20
>  Best regards,
>  Shinya Kato
>  NTT OSS Center

--=20
Regards,
Japin Li
ChengDu WenWu Information Technology Co., Ltd.