Re: WAL_LOG CREATE DATABASE strategy broken for non-standard page layouts

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:
>
> 1. The promoted standby has a zeroed VM, so VACUUM FREEZE sets the
>    bits again, emitting PRUNE records with no FPI for the VM buffer.
> 2. The old primary, rejoined as standby, still has the bits set with
>    an older page LSN, so replay takes the redo branch - but
>    visibilitymap_set() is a no-op there (bits already set) and the
>    buffer stays clean.
> 3. Assert(BufferIsDirty(vmbuffer)) fires, and the node crash-loops on
>    that record.
>
> 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