Re: [Patch]The Case For WAL-Logging pg_upgrade

On 06/08/2026 01:17, John Naylor wrote:
> On Wed, Aug 5, 2026 at 9:36 PM Bohyun Lee
> <bohyun(dot)lee(at)databricks(dot)com> wrote:
>> The GUCs are introduced because we cannot assume the standby's
>> storage layout exactly matches the primary's, neither where the
>> retained pre-upgrade directory sits, nor how its files are
>> physically placed. It also depends on how the cluster intends to
>> use the standby. For instance, if the operator wants to keep the
>> standby as a rollback target, it may be worthwhile to use a
>> different transfer mode via the newly introduced
>> pg_upgrade_standby_transfer_mode GUC, which I believe is useful.
>> Nevertheless, the reconstructed cluster will be logically
>> identical, even if the physical representation diverges.
>
> Given the above design concepts, I still think WAL is fundamentally
> the wrong mechanism for this.

Can you elaborate? Do you think the changes that pg_upgrade makes should
be written somewhere else than WAL, or is this just about the transfer
mode setting, or something else? How would you do it?

- Heikki