Re: Error pg_upgrade version 11 to 15

On Mon, Aug 18, 2025 at 03:16:46PM -0400, Andrew Dunstan wrote:
> Template1 normally has an OID of 1, but this database has an apparent OID of
> 18344416. Maybe this has been the result of a previous upgrade - we don't
> have enough information. I don't think pg_upgrade attempts to preserve
> database OIDs.

It does as of v15 [0].

I concur with Tom that this is most likely due to template1 not being
marked as a template database in the source cluster.  We could presumably
hack pg_upgrade to deal with this for template1 and postgres databases
(e.g., by preemptively setting datistemplate = f on the new cluster).
Changes to template0 are likely harder to deal with.  Since pg_dump uses it
as the template for databases it creates, we'd have to wait until all other
databases are restored before re-creating it.  Plus, we'd probably have to
first create a fresh template0 clone (with the source template0's encoding
and locale settings) so that there was something to use as a template for
template0.  There might be other problems, and I'm not sure it's worth the
effort, anyway.

[0] https://postgr.es/c/aa01051

-- 
nathan