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

On Tue, Aug 17, 2021 at 11:07 PM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Tue, Aug 17, 2021 at 12:42 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > Actually though ... I've not read the patch, but what does it do about
> > the fact that the postgres and template0 DBs do not have stable OIDs?
> > I cannot imagine any way to force those to match across PG versions
> > that would not be an unsustainable crock.
>
> Well, it's interesting that you mention that, because there's a
> comment in the patch that probably has to do with this:
>
> + /*
> + * Make sure that pg_upgrade does not change database OID. Don't care
> + * about "postgres" database, backend will assign it fixed OID anyway.
> + * ("template1" has fixed OID too but the value 1 should not collide with
> + * any other OID so backend pays no attention to it.)
> + */
>
In the original patch the author intended to avoid dumping the
postgres DB OID like below:
+ if (dopt->binary_upgrade && dbCatId.oid != PostgresDbOid)

Since postgres OID is not hardcoded/fixed I removed the check.
My bad I missed updating the comment section. Sorry for the confusion.

Regards,
Shruthi KC
EnterpriseDB: http://www.enterprisedb.com