Re: pg_filenode_relation(0,0) elog

On Fri, Jun 11, 2021 at 11:51:35PM -0400, Tom Lane wrote:
> Justin Pryzby <pryzby(at)telsasoft(dot)com> writes:
> > Per sqlsmith.
> > postgres=# SELECT pg_filenode_relation(0,0);
> > ERROR: unexpected duplicate for tablespace 0, relfilenode 0
>
> Ugh.
>
> > The usual expectation is that sql callable functions should return null rather
> > than hitting elog().
>
> Agreed, but you should put the short-circuit into the SQL-callable
> function, ie pg_filenode_relation. Lower-level callers ought not be
> passing junk data.

Right. I spent inadequate time reading output of git grep.

> Likely it should check the reltablespace, too.

I don't think so. The docs say:
https://www.postgresql.org/docs/current/functions-admin.html#FUNCTIONS-ADMIN-DBLOCATION
|For a relation in the database's default tablespace, the tablespace can be specified as zero.

Also, that would breaks expected/alter_table.out for the same reason.

diff --git a/src/backend/utils/adt/dbsize.c b/src/backend/utils/adt/dbsize.c
index 3c70bb5943..144aca1099 100644
--- a/src/backend/utils/adt/dbsize.c
+++ b/src/backend/utils/adt/dbsize.c
@@ -905,6 +905,9 @@ pg_filenode_relation(PG_FUNCTION_ARGS)
Oid relfilenode = PG_GETARG_OID(1);
Oid heaprel = InvalidOid;

+ if (!OidIsValid(relfilenode))
+ PG_RETURN_NULL();
+
heaprel = RelidByRelfilenode(reltablespace, relfilenode);

if (!OidIsValid(heaprel))