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

On Mon, Dec 13, 2021 at 8:43 PM Shruthi Gowda <gowdashru(at)gmail(dot)com> wrote:
>
> On Mon, Dec 6, 2021 at 11:25 PM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> >
> > On Sun, Dec 5, 2021 at 11:44 PM Sadhuprasad Patro <b(dot)sadhu(at)gmail(dot)com> wrote:
> > > 3.
> > > @@ -504,11 +525,15 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
> > > */
> > > pg_database_rel = table_open(DatabaseRelationId, RowExclusiveLock);
> > >
> > > - do
> > > + /* Select an OID for the new database if is not explicitly configured. */
> > > + if (!OidIsValid(dboid))
> > > {
> > > - dboid = GetNewOidWithIndex(pg_database_rel, DatabaseOidIndexId,
> > > - Anum_pg_database_oid);
> > > - } while (check_db_file_conflict(dboid));
> > >
> > > I think we need to do 'check_db_file_conflict' for the USER given OID
> > > also.. right? It may already be present.
> >
> > Hopefully, if that happens, we straight up fail later on.
>
> That's right. If a database with user-specified OID exists, the
> createdb fails with a "duplicate key value" error.
> If just a data directory with user-specified OID exists,
> MakePGDirectory() fails to create the directory and the cleanup
> callback createdb_failure_callback() removes the directory that was
> not created by 'createdb()' function.
> The subsequent create database call with the same OID will succeed.
> Should we handle the case where a data directory exists and the
> corresponding DB with that oid does not exist? I presume this
> situation doesn't arise unless the user tries to create directories in
> the data path. Any thoughts?

I have updated the DBOID preserve patch to handle this case and
generated the latest patch on top of your v7-001-preserve-relfilenode
patch.

Thanks & Regards
Shruthi KC
EnterpriseDB: http://www.enterprisedb.com