Feedback-ID: i0fe9450f:Fastmail
Date: Mon, 31 Aug 2026 14:37:46 +0900
From: Michael Paquier <michael@paquier.xyz>
To: Rogers Wang <rogers.ww@qq.com>
Cc: pgsql-hackers@lists.postgresql.org,
	Matthias van de Meent <boekewurm+postgres@gmail.com>,
	=?iso-8859-1?Q?=C1lvaro?= Herrera <alvherre@kurilemu.de>,
	melanieplageman@gmail.com
Subject: Re: WAL_LOG CREATE DATABASE strategy broken for non-standard page
 layouts
Message-ID: <apUTKUUvYfG3SlBF@paquier.xyz>
References: <202602021525.qv4m7oge4eca@alvherre.pgsql>
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On Mon, Aug 24, 2026 at 01:04:44AM +0800, Rogers Wang wrote:
> What changed since the last discussion
> --------------------------------------
> The divergence was assessed back then as "not actively harmful". That
> no longer holds in v19: commit add323da40a added
> Assert(BufferIsDirty(vmbuffer)) to heap_xlog_prune_freeze(), which
> makes the divergence fatal on assert builds after a switchover:
>=20
> 1. The promoted standby has a zeroed VM, so VACUUM FREEZE sets the
> =A0 =A0bits again, emitting PRUNE records with no FPI for the VM buffer.
> 2. The old primary, rejoined as standby, still has the bits set with
> =A0 =A0an older page LSN, so replay takes the redo branch - but
> =A0 =A0visibilitymap_set() is a no-op there (bits already set) and the
> =A0 =A0buffer stays clean.
> 3. Assert(BufferIsDirty(vmbuffer)) fires, and the node crash-loops on
> =A0 =A0that record.
>=20
> And even without assertions, the new database on the standby silently
> loses all all-visible/all-frozen bits and all free space data of every
> copied relation.

Hmm.  This warrants an open item for v19, at least to be discussed.
Adding Melanie in CC as the committer of add323da40a.
--
Michael

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