Fix failure to ignore leftover temp tables after a server crash.

During crash recovery, we remove disk files belonging to temporary tables,
but the system catalog entries for such tables are intentionally not
cleaned up right away.  Instead, the first backend that uses a temp schema
is expected to clean out any leftover objects therein.  This approach
requires that we be careful to ignore leftover temp tables (since any
actual access attempt would fail), *even if their BackendId matches our
session*, if we have not yet established use of the session's corresponding
temp schema.  That worked fine in the past, but was broken by commit
debcec7dc3 which incorrectly removed the
rd_islocaltemp relcache flag.  Put it back, and undo various changes
that substituted tests like "rel->rd_backend == MyBackendId" for use
of a state-aware flag.  Per trouble report from Heikki Linnakangas.

Back-patch to 9.1 where the erroneous change was made.  In the back
branches, be careful to add rd_islocaltemp in a spot in the struct that
was alignment padding before, so as not to break existing add-on code.

src/backend/catalog/toasting.c

@@ -196,7 +196,7 @@ create_toast_table(Relation rel, Oid toastOid, Oid toastIndexOid, Datum reloptio
 	 * Toast tables for regular relations go in pg_toast; those for temp
 	 * relations go into the per-backend temp-toast-table namespace.
 	 */
-	if (RelationUsesTempNamespace(rel))
+	if (isTempOrToastNamespace(rel->rd_rel->relnamespace))
 		namespaceid = GetTempToastNamespace();
 	else
 		namespaceid = PG_TOAST_NAMESPACE;

src/backend/commands/copy.c

@@ -806,7 +806,7 @@ DoCopy(const CopyStmt *stmt, const char *queryString)
 		Assert(rel);
 
 		/* check read-only transaction */
-		if (XactReadOnly && rel->rd_backend != MyBackendId)
+		if (XactReadOnly && !rel->rd_islocaltemp)
 			PreventCommandIfReadOnly("COPY FROM");
 
 		cstate = BeginCopyFrom(rel, stmt->filename,

src/backend/commands/sequence.c

@@ -553,7 +553,7 @@ nextval_internal(Oid relid)
 						RelationGetRelationName(seqrel))));
 
 	/* read-only transactions may only modify temp sequences */
-	if (seqrel->rd_backend != MyBackendId)
+	if (!seqrel->rd_islocaltemp)
 		PreventCommandIfReadOnly("nextval()");
 
 	if (elm->last != elm->cached)		/* some numbers were cached */
@@ -846,7 +846,7 @@ do_setval(Oid relid, int64 next, bool iscalled)
 						RelationGetRelationName(seqrel))));
 
 	/* read-only transactions may only modify temp sequences */
-	if (seqrel->rd_backend != MyBackendId)
+	if (!seqrel->rd_islocaltemp)
 		PreventCommandIfReadOnly("setval()");
 
 	/* lock page' buffer and read tuple */

src/backend/commands/tablecmds.c

@@ -1451,13 +1451,20 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
 					 errmsg("inherited relation \"%s\" is not a table",
 							parent->relname)));
 		/* Permanent rels cannot inherit from temporary ones */
-		if (relpersistence != RELPERSISTENCE_TEMP
-			&& RelationUsesTempNamespace(relation))
+		if (relpersistence != RELPERSISTENCE_TEMP &&
+			relation->rd_rel->relpersistence == RELPERSISTENCE_TEMP)
 			ereport(ERROR,
 					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 					 errmsg("cannot inherit from temporary relation \"%s\"",
 							parent->relname)));
 
+		/* If existing rel is temp, it must belong to this session */
+		if (relation->rd_rel->relpersistence == RELPERSISTENCE_TEMP &&
+			!relation->rd_islocaltemp)
+			ereport(ERROR,
+					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					 errmsg("cannot inherit from temporary relation of another session")));
+
 		/*
 		 * We should have an UNDER permission flag for this, but for now,
 		 * demand that creator of a child table own the parent.
@@ -5768,6 +5775,10 @@ ATAddForeignKeyConstraint(AlteredTableInfo *tab, Relation rel,
 				ereport(ERROR,
 						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 						 errmsg("constraints on temporary tables may reference only temporary tables")));
+			if (!pkrel->rd_islocaltemp || !rel->rd_islocaltemp)
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("constraints on temporary tables must involve temporary tables of this session")));
 			break;
 	}
 
@@ -8884,13 +8895,27 @@ ATExecAddInherit(Relation child_rel, RangeVar *parent, LOCKMODE lockmode)
 	ATSimplePermissions(parent_rel, ATT_TABLE);
 
 	/* Permanent rels cannot inherit from temporary ones */
-	if (RelationUsesTempNamespace(parent_rel)
-		&& !RelationUsesTempNamespace(child_rel))
+	if (parent_rel->rd_rel->relpersistence == RELPERSISTENCE_TEMP &&
+		child_rel->rd_rel->relpersistence != RELPERSISTENCE_TEMP)
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("cannot inherit from temporary relation \"%s\"",
 						RelationGetRelationName(parent_rel))));
 
+	/* If parent rel is temp, it must belong to this session */
+	if (parent_rel->rd_rel->relpersistence == RELPERSISTENCE_TEMP &&
+		!parent_rel->rd_islocaltemp)
+		ereport(ERROR,
+				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				 errmsg("cannot inherit from temporary relation of another session")));
+
+	/* Ditto for the child */
+	if (child_rel->rd_rel->relpersistence == RELPERSISTENCE_TEMP &&
+		!child_rel->rd_islocaltemp)
+		ereport(ERROR,
+				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				 errmsg("cannot inherit to temporary relation of another session")));
+
 	/*
 	 * Check for duplicates in the list of parents, and determine the highest
 	 * inhseqno already present; we'll use the next one for the new parent.

src/backend/utils/adt/dbsize.c

@@ -260,6 +260,9 @@ pg_tablespace_size_name(PG_FUNCTION_ARGS)
 
 /*
  * calculate size of (one fork of) a relation
+ *
+ * Note: we can safely apply this to temp tables of other sessions, so there
+ * is no check here or at the call sites for that.
  */
 static int64
 calculate_relation_size(RelFileNode *rfn, BackendId backend, ForkNumber forknum)
@@ -314,7 +317,7 @@ pg_relation_size(PG_FUNCTION_ARGS)
 	 * that makes queries like "SELECT pg_relation_size(oid) FROM pg_class"
 	 * less robust, because while we scan pg_class with an MVCC snapshot,
 	 * someone else might drop the table. It's better to return NULL for
-	 * alread-dropped tables than throw an error and abort the whole query.
+	 * already-dropped tables than throw an error and abort the whole query.
 	 */
 	if (rel == NULL)
 		PG_RETURN_NULL();

src/backend/utils/cache/relcache.c

@@ -853,20 +853,33 @@ RelationBuildDesc(Oid targetRelId, bool insertIt)
 		case RELPERSISTENCE_UNLOGGED:
 		case RELPERSISTENCE_PERMANENT:
 			relation->rd_backend = InvalidBackendId;
+			relation->rd_islocaltemp = false;
 			break;
 		case RELPERSISTENCE_TEMP:
 			if (isTempOrToastNamespace(relation->rd_rel->relnamespace))
+			{
 				relation->rd_backend = MyBackendId;
+				relation->rd_islocaltemp = true;
+			}
 			else
 			{
 				/*
-				 * If it's a local temp table, but not one of ours, we have to
-				 * use the slow, grotty method to figure out the owning
-				 * backend.
+				 * If it's a temp table, but not one of ours, we have to use
+				 * the slow, grotty method to figure out the owning backend.
+				 *
+				 * Note: it's possible that rd_backend gets set to MyBackendId
+				 * here, in case we are looking at a pg_class entry left over
+				 * from a crashed backend that coincidentally had the same
+				 * BackendId we're using.  We should *not* consider such a
+				 * table to be "ours"; this is why we need the separate
+				 * rd_islocaltemp flag.  The pg_class entry will get flushed
+				 * if/when we clean out the corresponding temp table namespace
+				 * in preparation for using it.
 				 */
 				relation->rd_backend =
 					GetTempNamespaceBackendId(relation->rd_rel->relnamespace);
 				Assert(relation->rd_backend != InvalidBackendId);
+				relation->rd_islocaltemp = false;
 			}
 			break;
 		default:
@@ -1387,6 +1400,7 @@ formrdesc(const char *relationName, Oid relationReltype,
 	relation->rd_createSubid = InvalidSubTransactionId;
 	relation->rd_newRelfilenodeSubid = InvalidSubTransactionId;
 	relation->rd_backend = InvalidBackendId;
+	relation->rd_islocaltemp = false;
 
 	/*
 	 * initialize relation tuple form
@@ -2538,16 +2552,19 @@ RelationBuildLocalRelation(const char *relname,
 	/* needed when bootstrapping: */
 	rel->rd_rel->relowner = BOOTSTRAP_SUPERUSERID;
 
-	/* set up persistence; rd_backend is a function of persistence type */
+	/* set up persistence and relcache fields dependent on it */
 	rel->rd_rel->relpersistence = relpersistence;
 	switch (relpersistence)
 	{
 		case RELPERSISTENCE_UNLOGGED:
 		case RELPERSISTENCE_PERMANENT:
 			rel->rd_backend = InvalidBackendId;
+			rel->rd_islocaltemp = false;
 			break;
 		case RELPERSISTENCE_TEMP:
+			Assert(isTempOrToastNamespace(relnamespace));
 			rel->rd_backend = MyBackendId;
+			rel->rd_islocaltemp = true;
 			break;
 		default:
 			elog(ERROR, "invalid relpersistence: %c", relpersistence);

src/include/utils/rel.h

@@ -81,6 +81,7 @@ typedef struct RelationData
 	struct SMgrRelationData *rd_smgr;	/* cached file handle, or NULL */
 	int			rd_refcnt;		/* reference count */
 	BackendId	rd_backend;		/* owning backend id, if temporary relation */
+	bool		rd_islocaltemp; /* rel is a temp rel of this session */
 	bool		rd_isnailed;	/* rel is nailed in cache */
 	bool		rd_isvalid;		/* relcache entry is valid */
 	char		rd_indexvalid;	/* state of rd_indexlist: 0 = not valid, 1 =
@@ -362,22 +363,16 @@ typedef struct StdRdOptions
 #define RelationUsesLocalBuffers(relation) \
 	((relation)->rd_rel->relpersistence == RELPERSISTENCE_TEMP)
 
-/*
- * RelationUsesTempNamespace
- *		True if relation's catalog entries live in a private namespace.
- */
-#define RelationUsesTempNamespace(relation) \
-	((relation)->rd_rel->relpersistence == RELPERSISTENCE_TEMP)
-
 /*
  * RELATION_IS_LOCAL
  *		If a rel is either temp or newly created in the current transaction,
- *		it can be assumed to be visible only to the current backend.
+ *		it can be assumed to be accessible only to the current backend.
+ *		This is typically used to decide that we can skip acquiring locks.
  *
  * Beware of multiple eval of argument
  */
 #define RELATION_IS_LOCAL(relation) \
-	((relation)->rd_backend == MyBackendId || \
+	((relation)->rd_islocaltemp || \
 	 (relation)->rd_createSubid != InvalidSubTransactionId)
 
 /*
@@ -387,8 +382,8 @@ typedef struct StdRdOptions
  * Beware of multiple eval of argument
  */
 #define RELATION_IS_OTHER_TEMP(relation) \
-	((relation)->rd_rel->relpersistence == RELPERSISTENCE_TEMP \
-	&& (relation)->rd_backend != MyBackendId)
+	((relation)->rd_rel->relpersistence == RELPERSISTENCE_TEMP && \
+	 !(relation)->rd_islocaltemp)
 
 /* routines in utils/cache/relcache.c */
 extern void RelationIncrementReferenceCount(Relation rel);