Re: Implement waiting for wal lsn replay: reloaded

On Thu, Jan 29, 2026 at 9:47 AM Alexander Korotkov <aekorotkov(at)gmail(dot)com> wrote:
> On Tue, Jan 27, 2026 at 3:14 AM Xuneng Zhou <xunengzhou(at)gmail(dot)com> wrote:
> > Heikki spotted a misplaced wake-up call for replay waiters in
> > PerformWalRecovery. He suggested that the WaitLSNWakeup needs to be
> > invoked immediately after wal record is applied to avoid the potential
> > missed wake-ups when recovery stops/pauses/promotes. It makes sense to
> > me. Please check the attached patch to fix that.
>
> Pushed, thank you!

I've assembled small patches, which I think worth pushing before v19 FF.

1. Avoid syscache lookup in WaitStmtResultDesc(). This is [1] patch,
but I've removed redundant comment in ExecWaitStmt(), which explained
the same as WaitStmtResultDesc() comment.
2. Use WAIT FOR LSN in wait_for_catchup(). I made the following
changes: fallback to polling on not_in_recovery result instead of
croaking, avoid separate pg_is_in_recovery() query, comment why we
may face the recovery conflict and why it is safe to detect this by
the error string.
3. A paragraph to the docs about possible recovery conflicts and their reason.

I'm going to push this on Monday if no objections.

Links.
1. https://www.postgresql.org/message-id/CABPTF7U%2BSUnJX_woQYGe%3D%3DR9Oz%2B-V6X0VO2stBLPGfJmH_LEhw%40mail.gmail.com
2. https://www.postgresql.org/message-id/CABPTF7X0n%3DR50z2fBpj3EbYYz04Ab0-DHJa%2BJfoAEny62QmUdg%40mail.gmail.com

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Regards,
Alexander Korotkov
Supabase