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From: Xuneng Zhou <[email protected]>
To: Bertrand Drouvot <[email protected]>
Cc: Alexander Lakhin <[email protected]>
Cc: pgsql-hackers <[email protected]>
Subject: Re: t/035_standby_logical_decoding.pl might fail on attempt to read wrong timeline
Date: Sat, 6 Jun 2026 20:56:10 +0800
Message-ID: <CABPTF7UqSh4LCA_Lf2owJg5VBs5jteBfb5q4Jt9BiOdq8bMH8w@mail.gmail.com> (raw)
In-Reply-To: <aiP/X1FThlZRCFiN@bdtpg>
References: <[email protected]>
	<aiP/X1FThlZRCFiN@bdtpg>

Hi Bertrand,

On Sat, Jun 6, 2026 at 7:07 PM Bertrand Drouvot
<[email protected]> wrote:
>
> Hi Alexander,
>
> On Sat, Jun 06, 2026 at 12:00:00PM +0300, Alexander Lakhin wrote:
> > Hello hackers,
> >
> > That is, walsender requested WAL segment for timeline 1, while in a
> > successful run, it reads WAL for timeline 2.
> >
> > I've managed to reproduce this failure with:
>
> Thanks for the report and the repro!
>
> > As far as I can see, the timeline is chosen in logical_read_xlog_page()
> > depending on the recovery state:
> >         am_cascading_walsender = RecoveryInProgress();
> >
> >         if (am_cascading_walsender)
> >                 GetXLogReplayRecPtr(&currTLI);
> >         else
> >                 currTLI = GetWALInsertionTimeLine();
>
> Yeah, it looks like there is a race condition here. I think we should check if
> the insertion timeline has already been set (like the walsummarizer is doing).
>
> I'll work on a fix early next week.

This looks like the right direction to fix. We may want to apply
similar logic to read_local_xlog_page_guts as well. Although the
failure is reported in walsender, SQL logical decoding uses the local
WAL reader and has the same recovery/TLI pattern.

--
Regards,
Xuneng Zhou
HighGo Software Co., Ltd.

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