Re: pg_filenode_relation(0,0) elog

On Fri, Jun 11, 2021 at 11:51:35PM -0400, Tom Lane wrote:
> Justin Pryzby <pryzby@telsasoft.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))