Re: pg_rewind with cascade standby doesn't work well

On Wed, Sep 20, 2023 at 11:46:45AM +0900, Kuwamura Masaki wrote:
> I also found a bug (maybe). If we call `CreateRestartPoint()` during
> crash-recovery, the assertion fails at ComputeXidHorizon() in procarray.c.
> It's inherently orthogonal to the problem I already reported. So you can
> reproduce this at HEAD with this procedure.
>
> 1. Start primary and standby server
> 2. Modify checkpoint_timeout to 1h on standby
> 3. Insert 10^10 records and concurrently run CHECKPOINT every second on
> primary
> 4. Do an immediate stop on both standby and primary at the end of the insert
> 5. Modify checkpoint_timeout to 30 on standby
> 6. Remove standby.signal on standby
> 7. Restart standby (it will start crash-recovery)
> 8. Assertion failure is raised shortly
>
> I think this is because `TruncateSUBTRANS();` in `CreateRestartPoint()` is
> called but `StartupSUBTRANS()` isn't called yet. In `StartupXLOG()`, we
> call
> `StartupSUBTRANS()` if `(ArchiveRecoveryRequested && EnableHotStandby)`.
> However, in `CreateRestartPoint()`, we call `TruncateSUBTRANS()` if
> `(EnableHotStandby)`. I guess the difference causes this bug. The latter
> possibly be called even crash-recovery while former isn't.
> The attached patch 0002 fixes it. I think we could discuss about this bug
> in
> another thread if needed.

This is a known issue. I guess that the same as this thread and this
CF entry:
https://commitfest.postgresql.org/44/4244/
https://www.postgresql.org/message-id/flat/ZArVOMifjzE7f8W7(at)paquier(dot)xyz
--
Michael