Re: preserving db/ts/relfilenode OIDs across pg_upgrade (was Re: storing an explicit nonce)

On Mon, Aug 23, 2021 at 5:12 PM Stephen Frost <sfrost(at)snowman(dot)net> wrote:
> Regarding that ... I have to wonder just what promises we feel we've
> made when it comes to what a user is expected to be able to do with the
> new cluster *before* pg_upgrade is run on it. For my part, I sure feel
> like it's "nothing", in which case it seems like we can do things that
> we can't do with a running system, like literally just DROP and recreate
> with the correct OID of any databases we need to, or even push that back
> to the user to do that at initdb time with some kind of error thrown by
> pg_upgrade during the --check phase. "Initial databases have
> non-standard OIDs, recreate destination cluster with initdb
> --with-oid=12341" or something along those lines.

Yeah, possibly. Honestly, I find it weird that pg_upgrade expects the
new cluster to already exist. It seems like it would be more sensible
if it created the cluster itself. That's not entirely trivial, because
for example you have to create it with the correct locale settings and
stuff. But if you require the cluster to exist already, then you run
into the kinds of questions that you're asking here, and whether the
answer is "nothing" as you propose here or something more than that,
it's clearly not "whatever you want" nor anything close to that.

--
Robert Haas
EDB: http://www.enterprisedb.com