Don't scan partitioned tables.

Partitioned tables do not contain any data; only their unpartitioned
descendents need to be scanned.  However, the partitioned tables still
need to be locked, even though they're not scanned.  To make that
work, Append and MergeAppend relations now need to carry a list of
(unscanned) partitioned relations that must be locked, and InitPlan
must lock all partitioned result relations.

Aside from the obvious advantage of avoiding some work at execution
time, this has two other advantages.  First, it may improve the
planner's decision-making in some cases since the empty relation
might throw things off.  Second, it paves the way to getting rid of
the storage for partitioned tables altogether.

Amit Langote, reviewed by me.

Discussion: http://postgr.es/m/[email protected]

1 files changed, 56 insertions, 0 deletions

diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
index 3d6a3801c06..a72cffeb6e5 100644
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -43,6 +43,7 @@
 #include "executor/executor.h"
 #include "nodes/nodeFuncs.h"
 #include "parser/parsetree.h"
+#include "storage/lmgr.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
 
@@ -953,3 +954,58 @@ ShutdownExprContext(ExprContext *econtext, bool isCommit)
 
 	MemoryContextSwitchTo(oldcontext);
 }
+
+/*
+ * ExecLockNonLeafAppendTables
+ *
+ * Locks, if necessary, the tables indicated by the RT indexes contained in
+ * the partitioned_rels list.  These are the non-leaf tables in the partition
+ * tree controlled by a given Append or MergeAppend node.
+ */
+void
+ExecLockNonLeafAppendTables(List *partitioned_rels, EState *estate)
+{
+	PlannedStmt *stmt = estate->es_plannedstmt;
+	ListCell	*lc;
+
+	foreach(lc, partitioned_rels)
+	{
+		ListCell   *l;
+		Index	rti = lfirst_int(lc);
+		bool	is_result_rel = false;
+		Oid		relid = getrelid(rti, estate->es_range_table);
+
+		/* If this is a result relation, already locked in InitPlan */
+		foreach(l, stmt->nonleafResultRelations)
+		{
+			if (rti == lfirst_int(l))
+			{
+				is_result_rel = true;
+				break;
+			}
+		}
+
+		/*
+		 * Not a result relation; check if there is a RowMark that requires
+		 * taking a RowShareLock on this rel.
+		 */
+		if (!is_result_rel)
+		{
+			PlanRowMark *rc = NULL;
+
+			foreach(l, stmt->rowMarks)
+			{
+				if (((PlanRowMark *) lfirst(l))->rti == rti)
+				{
+					rc = lfirst(l);
+					break;
+				}
+			}
+
+			if (rc && RowMarkRequiresRowShareLock(rc->markType))
+				LockRelationOid(relid, RowShareLock);
+			else
+				LockRelationOid(relid, AccessShareLock);
+		}
+	}
+}