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From: Alexander Korotkov <aekorotkov@gmail.com>
Date: Fri, 18 Jul 2025 13:43:04 +0300
Message-ID: 
 <CAPpHfdurcDSPqHUeC4ho2+2J24-838PehWOmbipdnnCu=YBmjw@mail.gmail.com>
Subject: Re: Slot's restart_lsn may point to removed WAL segment after hard
 restart unexpectedly
To: vignesh C <vignesh21@gmail.com>
Cc: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>,
 Amit Kapila <amit.kapila16@gmail.com>,
	Vitaly Davydov <v.davydov@postgrespro.ru>, Tom Lane <tgl@sss.pgh.pa.us>,
	Alexander Lakhin <exclusion@gmail.com>,
 pgsql-hackers <pgsql-hackers@postgresql.org>,
	Masahiko Sawada <sawada.mshk@gmail.com>, "tomas@vondra.me" <tomas@vondra.me>
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On Wed, Jul 2, 2025 at 8:20=E2=80=AFPM vignesh C <vignesh21@gmail.com> wrot=
e:
> On Sun, 29 Jun 2025 at 11:52, Hayato Kuroda (Fujitsu)
> <kuroda.hayato@fujitsu.com> wrote:
> >
> > Dear hackers,
> >
> > Thanks everyone who are working on the bug. IIUC the remained task is
> > to add code comments for avoiding the same mistake again described here=
:
> >
> > > Sounds reasonable. As per analysis till now, it seems removal of new
> > > assert is correct and we just need to figure out the reason in all
> > > failure cases as to why the physical slot's restart_lsn goes backward=
,
> > > and then add a comment somewhere to ensure that we don't repeat a
> > > similar mistake in the future.
> >
> > I've wrote a draft for that. How do you think?
>
> I analyzed a scenario involving physical replication where the
> restart_lsn appears to go backward by fewer files:

This is indeed an interesting case.  But does restart_lsn go so much
backwards in this case?  I've checked the logs.  It looks like standby
requested a position several segments back, but restart_lsn keeps
increasing.

> I'm ok with adding the comments.

Thank you for your feedback!

------
Regards,
Alexander Korotkov
Supabase