Ignore temporary relations in RelidByRelfilenumber()

Temporary relations may share the same RelFileNumber with a permanent
relation, or other temporary relations associated with other sessions.

Being able to uniquely identify a temporary relation would require
RelidByRelfilenumber() to know about the proc number of the temporary
relation it wants to identify, something it is not designed for since
its introduction in f01d1ae3a1.

There are currently three callers of RelidByRelfilenumber():
- autoprewarm.
- Logical decoding, reorder buffer.
- pg_filenode_relation(), that attempts to find a relation OID based on
a tablespace OID and a RelFileNumber.

This makes the situation problematic particularly for the first two
cases, leading to the possibility of random ERRORs due to
inconsistencies that temporary relations can create in the cache
maintained by RelidByRelfilenumber().  The third case should be less of
an issue, as I suspect that there are few direct callers of
pg_filenode_relation().

The window where the ERRORs are happen is very narrow, requiring an OID
wraparound to create a lookup conflict in RelidByRelfilenumber() with a
temporary table reusing the same OID as another relation already cached.
The problem is easier to reach in workloads with a high OID consumption
rate, especially with a higher number of temporary relations created.

We could get pg_filenode_relation() and RelidByRelfilenumber() to work
with temporary relations if provided the means to identify them with an
optional proc number given in input, but the years have also shown that
we do not have a use case for it, yet.  Note that this could not be
backpatched if pg_filenode_relation() needs changes.  It is simpler to
ignore temporary relations.

Reported-by: Shenhao Wang <wangsh.fnst@fujitsu.com>
Author: Vignesh C <vignesh21@gmail.com>
Reviewed-By: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Reviewed-By: Robert Haas <robertmhaas@gmail.com>
Reviewed-By: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reviewed-By: Takamichi Osumi <osumi.takamichi@fujitsu.com>
Reviewed-By: Michael Paquier <michael@paquier.xyz>
Reviewed-By: Masahiko Sawada <sawada.mshk@gmail.com>
Reported-By: Shenhao Wang <wangsh.fnst@fujitsu.com>
Discussion: https://postgr.es/m/bbaaf9f9-ebb2-645f-54bb-34d6efc7ac42@fujitsu.com
Backpatch-through: 13

doc/src/sgml/func.sgml

@@ -27930,7 +27930,8 @@ postgres=# SELECT '0/0'::pg_lsn + pd.segment_number * ps.setting::int + :offset
         <function>pg_relation_filepath</function>.  For a relation in the
         database's default tablespace, the tablespace can be specified as zero.
         Returns <literal>NULL</literal> if no relation in the current database
-        is associated with the given values.
+        is associated with the given values, or if dealing with a temporary
+        relation.
        </para></entry>
       </row>
      </tbody>

src/backend/utils/adt/dbsize.c

@@ -921,6 +921,9 @@ pg_relation_filenode(PG_FUNCTION_ARGS)
  *
  * We don't fail but return NULL if we cannot find a mapping.
  *
+ * Temporary relations are not detected, returning NULL (see
+ * RelidByRelfilenumber() for the reasons).
+ *
  * InvalidOid can be passed instead of the current database's default
  * tablespace.
  */

src/backend/utils/cache/relfilenumbermap.c

@@ -132,6 +132,11 @@ InitializeRelfilenumberMap(void)
  * Map a relation's (tablespace, relfilenumber) to a relation's oid and cache
  * the result.
  *
+ * A temporary relation may share its relfilenumber with a permanent relation
+ * or temporary relations created in other backends.  Being able to uniquely
+ * identify a temporary relation would require a backend's proc number, which
+ * we do not know about.  Hence, this function ignores this case.
+ *
  * Returns InvalidOid if no relation matching the criteria could be found.
  */
 Oid
@@ -211,6 +216,9 @@ RelidByRelfilenumber(Oid reltablespace, RelFileNumber relfilenumber)
 		{
 			Form_pg_class classform = (Form_pg_class) GETSTRUCT(ntp);
 
+			if (classform->relpersistence == RELPERSISTENCE_TEMP)
+				continue;
+
 			if (found)
 				elog(ERROR,
 					 "unexpected duplicate for tablespace %u, relfilenumber %u",

src/test/regress/expected/alter_table.out

@@ -3462,12 +3462,15 @@ SELECT conname as constraint, obj_description(oid, 'pg_constraint') as comment F
 -- filenode function call can return NULL for a relation dropped concurrently
 -- with the call's surrounding query, so ignore a NULL mapped_oid for
 -- relations that no longer exist after all calls finish.
+-- Temporary relations are ignored, as not supported by pg_filenode_relation().
 CREATE TEMP TABLE filenode_mapping AS
 SELECT
     oid, mapped_oid, reltablespace, relfilenode, relname
 FROM pg_class,
     pg_filenode_relation(reltablespace, pg_relation_filenode(oid)) AS mapped_oid
-WHERE relkind IN ('r', 'i', 'S', 't', 'm') AND mapped_oid IS DISTINCT FROM oid;
+WHERE relkind IN ('r', 'i', 'S', 't', 'm')
+  AND relpersistence != 't'
+  AND mapped_oid IS DISTINCT FROM oid;
 SELECT m.* FROM filenode_mapping m LEFT JOIN pg_class c ON c.oid = m.oid
 WHERE c.oid IS NOT NULL OR m.mapped_oid IS NOT NULL;
  oid | mapped_oid | reltablespace | relfilenode | relname 

src/test/regress/expected/create_table.out

@@ -92,6 +92,18 @@ ERROR:  tables declared WITH OIDS are not supported
 -- but explicitly not adding oids is still supported
 CREATE TEMP TABLE withoutoid() WITHOUT OIDS; DROP TABLE withoutoid;
 CREATE TEMP TABLE withoutoid() WITH (oids = false); DROP TABLE withoutoid;
+-- temporary tables are ignored by pg_filenode_relation().
+CREATE TEMP TABLE relation_filenode_check(c1 int);
+SELECT relpersistence,
+  pg_filenode_relation (reltablespace, pg_relation_filenode(oid))
+  FROM pg_class
+  WHERE relname = 'relation_filenode_check';
+ relpersistence | pg_filenode_relation 
+----------------+----------------------
+ t              | 
+(1 row)
+
+DROP TABLE relation_filenode_check;
 -- check restriction with default expressions
 -- invalid use of column reference in default expressions
 CREATE TABLE default_expr_column (id int DEFAULT (id));

src/test/regress/sql/alter_table.sql

@@ -2179,13 +2179,15 @@ SELECT conname as constraint, obj_description(oid, 'pg_constraint') as comment F
 -- filenode function call can return NULL for a relation dropped concurrently
 -- with the call's surrounding query, so ignore a NULL mapped_oid for
 -- relations that no longer exist after all calls finish.
+-- Temporary relations are ignored, as not supported by pg_filenode_relation().
 CREATE TEMP TABLE filenode_mapping AS
 SELECT
     oid, mapped_oid, reltablespace, relfilenode, relname
 FROM pg_class,
     pg_filenode_relation(reltablespace, pg_relation_filenode(oid)) AS mapped_oid
-WHERE relkind IN ('r', 'i', 'S', 't', 'm') AND mapped_oid IS DISTINCT FROM oid;
+WHERE relkind IN ('r', 'i', 'S', 't', 'm')
-
+  AND relpersistence != 't'
+  AND mapped_oid IS DISTINCT FROM oid;
 SELECT m.* FROM filenode_mapping m LEFT JOIN pg_class c ON c.oid = m.oid
 WHERE c.oid IS NOT NULL OR m.mapped_oid IS NOT NULL;
 

src/test/regress/sql/create_table.sql

@@ -62,6 +62,14 @@ CREATE TABLE withoid() WITH (oids = true);
 CREATE TEMP TABLE withoutoid() WITHOUT OIDS; DROP TABLE withoutoid;
 CREATE TEMP TABLE withoutoid() WITH (oids = false); DROP TABLE withoutoid;
 
+-- temporary tables are ignored by pg_filenode_relation().
+CREATE TEMP TABLE relation_filenode_check(c1 int);
+SELECT relpersistence,
+  pg_filenode_relation (reltablespace, pg_relation_filenode(oid))
+  FROM pg_class
+  WHERE relname = 'relation_filenode_check';
+DROP TABLE relation_filenode_check;
+
 -- check restriction with default expressions
 -- invalid use of column reference in default expressions
 CREATE TABLE default_expr_column (id int DEFAULT (id));