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, 9 insertions, 5 deletions

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 89e1946fc26..c80c9992c9f 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -199,7 +199,7 @@ static CteScan *make_ctescan(List *qptlist, List *qpqual,
 			 Index scanrelid, int ctePlanId, int cteParam);
 static WorkTableScan *make_worktablescan(List *qptlist, List *qpqual,
 				   Index scanrelid, int wtParam);
-static Append *make_append(List *appendplans, List *tlist);
+static Append *make_append(List *appendplans, List *tlist, List *partitioned_rels);
 static RecursiveUnion *make_recursive_union(List *tlist,
 					 Plan *lefttree,
 					 Plan *righttree,
@@ -273,7 +273,7 @@ static Result *make_result(List *tlist, Node *resconstantqual, Plan *subplan);
 static ProjectSet *make_project_set(List *tlist, Plan *subplan);
 static ModifyTable *make_modifytable(PlannerInfo *root,
 				 CmdType operation, bool canSetTag,
-				 Index nominalRelation,
+				 Index nominalRelation, List *partitioned_rels,
 				 List *resultRelations, List *subplans,
 				 List *withCheckOptionLists, List *returningLists,
 				 List *rowMarks, OnConflictExpr *onconflict, int epqParam);
@@ -1026,7 +1026,7 @@ create_append_plan(PlannerInfo *root, AppendPath *best_path)
 	 * parent-rel Vars it'll be asked to emit.
 	 */
 
-	plan = make_append(subplans, tlist);
+	plan = make_append(subplans, tlist, best_path->partitioned_rels);
 
 	copy_generic_path_info(&plan->plan, (Path *) best_path);
 
@@ -1134,6 +1134,7 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path)
 		subplans = lappend(subplans, subplan);
 	}
 
+	node->partitioned_rels = best_path->partitioned_rels;
 	node->mergeplans = subplans;
 
 	return (Plan *) node;
@@ -2314,6 +2315,7 @@ create_modifytable_plan(PlannerInfo *root, ModifyTablePath *best_path)
 							best_path->operation,
 							best_path->canSetTag,
 							best_path->nominalRelation,
+							best_path->partitioned_rels,
 							best_path->resultRelations,
 							subplans,
 							best_path->withCheckOptionLists,
@@ -5161,7 +5163,7 @@ make_foreignscan(List *qptlist,
 }
 
 static Append *
-make_append(List *appendplans, List *tlist)
+make_append(List *appendplans, List *tlist, List *partitioned_rels)
 {
 	Append	   *node = makeNode(Append);
 	Plan	   *plan = &node->plan;
@@ -5170,6 +5172,7 @@ make_append(List *appendplans, List *tlist)
 	plan->qual = NIL;
 	plan->lefttree = NULL;
 	plan->righttree = NULL;
+	node->partitioned_rels = partitioned_rels;
 	node->appendplans = appendplans;
 
 	return node;
@@ -6282,7 +6285,7 @@ make_project_set(List *tlist,
 static ModifyTable *
 make_modifytable(PlannerInfo *root,
 				 CmdType operation, bool canSetTag,
-				 Index nominalRelation,
+				 Index nominalRelation, List *partitioned_rels,
 				 List *resultRelations, List *subplans,
 				 List *withCheckOptionLists, List *returningLists,
 				 List *rowMarks, OnConflictExpr *onconflict, int epqParam)
@@ -6308,6 +6311,7 @@ make_modifytable(PlannerInfo *root,
 	node->operation = operation;
 	node->canSetTag = canSetTag;
 	node->nominalRelation = nominalRelation;
+	node->partitioned_rels = partitioned_rels;
 	node->resultRelations = resultRelations;
 	node->resultRelIndex = -1;	/* will be set correctly in setrefs.c */
 	node->plans = subplans;