Date: Fri, 11 Jun 2021 21:33:25 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: pgsql-hackers@lists.postgresql.org
Subject: pg_filenode_relation(0,0) elog
Message-ID: <20210612023324.GT16435@telsasoft.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
User-Agent: Mutt/1.9.4 (2018-02-28)
Archived-At: 
 <https://www.postgresql.org/message-id/20210612023324.GT16435%40telsasoft.com>
Precedence: bulk

Per sqlsmith.

postgres=# SELECT pg_filenode_relation(0,0);
ERROR:  unexpected duplicate for tablespace 0, relfilenode 0

postgres=# \errverbose 
ERROR:  XX000: unexpected duplicate for tablespace 0, relfilenode 0
LOCATION:  RelidByRelfilenode, relfilenodemap.c:220

The usual expectation is that sql callable functions should return null rather
than hitting elog().  This also means that sqlsmith has one fewer
false-positive error.

I think it should return NULL if passed invalid relfilenode, rather than
searching pg_class and then writing a pretty scary message about duplicates.

diff --git a/src/backend/utils/cache/relfilenodemap.c b/src/backend/utils/cache/relfilenodemap.c
index 56d7c73d33..5a5cf853bd 100644
--- a/src/backend/utils/cache/relfilenodemap.c
+++ b/src/backend/utils/cache/relfilenodemap.c
@@ -146,6 +146,9 @@ RelidByRelfilenode(Oid reltablespace, Oid relfilenode)
 	ScanKeyData skey[2];
 	Oid			relid;
 
+	if (!OidIsValid(relfilenode))
+		return InvalidOid;
+
 	if (RelfilenodeMapHash == NULL)
 		InitializeRelfilenodeMap();