Centralize executor's opening/closing of Relations for rangetable entries.

Create an array estate->es_relations[] paralleling the es_range_table,
and store references to Relations (relcache entries) there, so that any
given RT entry is opened and closed just once per executor run.  Scan
nodes typically still call ExecOpenScanRelation, but ExecCloseScanRelation
is no more; relation closing is now done centrally in ExecEndPlan.

This is slightly more complex than one would expect because of the
interactions with relcache references held in ResultRelInfo nodes.
The general convention is now that ResultRelInfo->ri_RelationDesc does
not represent a separate relcache reference and so does not need to be
explicitly closed; but there is an exception for ResultRelInfos in the
es_trig_target_relations list, which are manufactured by
ExecGetTriggerResultRel and have to be cleaned up by
ExecCleanUpTriggerState.  (That much was true all along, but these
ResultRelInfos are now more different from others than they used to be.)

To allow the partition pruning logic to make use of es_relations[] rather
than having its own relcache references, adjust PartitionedRelPruneInfo
to store an RT index rather than a relation OID.

Amit Langote, reviewed by David Rowley and Jesper Pedersen,
some mods by me

Discussion: https://postgr.es/m/468c85d9-540e-66a2-1dde-fec2b741e688@lab.ntt.co.jp

1 files changed, 36 insertions, 24 deletions

diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
index ba93b401046..a89ef2a482f 100644
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -25,7 +25,8 @@
  *		etc
  *
  *		ExecOpenScanRelation	Common code for scan node init routines.
- *		ExecCloseScanRelation
+ *
+ *		ExecGetRangeTableRelation		Fetch Relation for a rangetable entry.
  *
  *		executor_errposition	Report syntactic position of an error.
  *
@@ -107,6 +108,7 @@ CreateExecutorState(void)
 	estate->es_snapshot = InvalidSnapshot;	/* caller must initialize this */
 	estate->es_crosscheck_snapshot = InvalidSnapshot;	/* no crosscheck */
 	estate->es_range_table = NIL;
+	estate->es_relations = NULL;
 	estate->es_plannedstmt = NULL;
 
 	estate->es_junkFilter = NULL;
@@ -648,15 +650,9 @@ Relation
 ExecOpenScanRelation(EState *estate, Index scanrelid, int eflags)
 {
 	Relation	rel;
-	Oid			reloid;
 
-	/* Open the relation and verify lock was obtained upstream */
-	reloid = getrelid(scanrelid, estate->es_range_table);
-	rel = heap_open(reloid, NoLock);
-	Assert(IsParallelWorker() ||
-		   CheckRelationLockedByMe(rel,
-								   rt_fetch(scanrelid, estate->es_range_table)->rellockmode,
-								   true));
+	/* Open the relation. */
+	rel = ExecGetRangeTableRelation(estate, scanrelid);
 
 	/*
 	 * Complain if we're attempting a scan of an unscannable relation, except
@@ -674,24 +670,40 @@ ExecOpenScanRelation(EState *estate, Index scanrelid, int eflags)
 	return rel;
 }
 
-/* ----------------------------------------------------------------
- *		ExecCloseScanRelation
- *
- *		Close the heap relation scanned by a base-level scan plan node.
- *		This should be called during the node's ExecEnd routine.
- *
- * Currently, we do not release the lock acquired by ExecOpenScanRelation.
- * This lock should be held till end of transaction.  (There is a faction
- * that considers this too much locking, however.)
+/*
+ * ExecGetRangeTableRelation
+ *		Open the Relation for a range table entry, if not already done
  *
- * If we did want to release the lock, we'd have to repeat the logic in
- * ExecOpenScanRelation in order to figure out what to release.
- * ----------------------------------------------------------------
+ * The Relations will be closed again in ExecEndPlan().
  */
-void
-ExecCloseScanRelation(Relation scanrel)
+Relation
+ExecGetRangeTableRelation(EState *estate, Index rti)
 {
-	heap_close(scanrel, NoLock);
+	Relation	rel;
+
+	Assert(rti > 0 && rti <= list_length(estate->es_range_table));
+
+	rel = estate->es_relations[rti - 1];
+	if (rel == NULL)
+	{
+		/* First time through, so open the relation */
+		RangeTblEntry *rte = rt_fetch(rti, estate->es_range_table);
+
+		Assert(rte->rtekind == RTE_RELATION);
+
+		rel = estate->es_relations[rti - 1] = heap_open(rte->relid, NoLock);
+
+		/*
+		 * Verify that appropriate lock was obtained before execution.
+		 *
+		 * In the case of parallel query, only the leader would've obtained
+		 * the lock (that needs to be fixed, though).
+		 */
+		Assert(IsParallelWorker() ||
+			   CheckRelationLockedByMe(rel, rte->rellockmode, false));
+	}
+
+	return rel;
 }
 
 /*