From: Tom Lane <tgl@sss.pgh.pa.us>
To: Pierre Fortin <pf@pfortin.com>
cc: pgsql-general@lists.postgresql.org
Subject: Re: pg_upgrade: can I use same binary for old & new?
In-reply-to: <20250705125207.31b4d475@pfortin.com>
References: <20250705125207.31b4d475@pfortin.com>
Comments: In-reply-to Pierre Fortin <pf@pfortin.com>
	message dated "Sat, 05 Jul 2025 12:52:07 -0400"
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Date: Sat, 05 Jul 2025 13:04:55 -0400
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Pierre Fortin <pf@pfortin.com> writes:
> - my Linux distro (Mageia) is not setup to handle multiple versions of
>   postgres (installing 17.5 removes 15.13).

Ugh.  You cannot do pg_upgrade without a copy of the old postgres
server binary as well as the new one.  pg_upgrade by itself is not
capable of accessing either set of catalogs.

Way back when I was packaging PG for Red Hat, they didn't support
multiple concurrently-installed package versions either, so what I did
was to provide an auxiliary pg_upgrade package that contained an old
server binary as well as pg_upgrade itself.  Perhaps Mageia has done
something similar, or could be cajoled to once you point out that
their packaging makes it impossible to do an upgrade.

If that path yields no joy, you'll need to use a hand-built copy of
one PG version or the other while performing the upgrade.  Might want
to think about migrating to some less PG-unfriendly distro while
you are at it.

			regards, tom lane