Message-ID: <b1e5047b-e322-4fb5-94f3-474f9425bcaa@iki.fi>
Date: Thu, 6 Aug 2026 10:43:47 +0300
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Subject: Re: [Patch]The Case For WAL-Logging pg_upgrade
To: John Naylor <johncnaylorls@gmail.com>,
 Bohyun Lee <bohyun.lee@databricks.com>
Cc: pgsql-hackers@lists.postgresql.org
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From: Heikki Linnakangas <hlinnaka@iki.fi>
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On 06/08/2026 01:17, John Naylor wrote:
> On Wed, Aug 5, 2026 at 9:36 PM Bohyun Lee
> <bohyun.lee@databricks.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