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/6837c359-45c4-8044-34d1-736756335a15@lab.ntt.co.jp

1 files changed, 21 insertions, 1 deletions

diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index f5cd65d8a0d..023ea0081a0 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -844,6 +844,22 @@ InitPlan(QueryDesc *queryDesc, int eflags)
 		estate->es_num_result_relations = numResultRelations;
 		/* es_result_relation_info is NULL except when within ModifyTable */
 		estate->es_result_relation_info = NULL;
+
+		/*
+		 * In the partitioned result relation case, lock the non-leaf result
+		 * relations too.  We don't however need ResultRelInfos for them.
+		 */
+		if (plannedstmt->nonleafResultRelations)
+		{
+			foreach(l, plannedstmt->nonleafResultRelations)
+			{
+				Index		resultRelationIndex = lfirst_int(l);
+				Oid			resultRelationOid;
+
+				resultRelationOid = getrelid(resultRelationIndex, rangeTable);
+				LockRelationOid(resultRelationOid, RowExclusiveLock);
+			}
+		}
 	}
 	else
 	{
@@ -858,7 +874,11 @@ InitPlan(QueryDesc *queryDesc, int eflags)
 	/*
 	 * Similarly, we have to lock relations selected FOR [KEY] UPDATE/SHARE
 	 * before we initialize the plan tree, else we'd be risking lock upgrades.
-	 * While we are at it, build the ExecRowMark list.
+	 * While we are at it, build the ExecRowMark list.  Any partitioned child
+	 * tables are ignored here (because isParent=true) and will be locked by
+	 * the first Append or MergeAppend node that references them.  (Note that
+	 * the RowMarks corresponding to partitioned child tables are present in
+	 * the same list as the rest, i.e., plannedstmt->rowMarks.)
 	 */
 	estate->es_rowMarks = NIL;
 	foreach(l, plannedstmt->rowMarks)