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

On Tue, Aug 24, 2021 at 2:16 PM Bruce Momjian <bruce@momjian.us> wrote:
> One other issue --- the more that pg_upgrade preserves, the more likely
> pg_upgrade will break when some internal changes happen in Postgres.
> Therefore, if you want pg_upgrade to preserve something, you have to
> have a good reason --- even code simplicity might not be a sufficient
> reason.

While I accept that as a general principle, I don't think it's really
applicable in this case. pg_upgrade already knows all about
relfilenodes; it has a source file called relfilenode.c. I don't see
that a pg_upgrade that preserves relfilenodes is any more or less
likely to break in the future than a pg_upgrade that renumbers all the
files so that the relation OID and the relfilenode are equal. You've
got about the same amount of reliance on the on-disk layout either
way.

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