Expand partitioned table RTEs level by level, without flattening.

Flattening the partitioning hierarchy at this stage makes various
desirable optimizations difficult.  The original use case for this
patch was partition-wise join, which wants to match up the partitions
in one partitioning hierarchy with those in another such hierarchy.
However, it now seems that it will also be useful in making partition
pruning work using the PartitionDesc rather than constraint exclusion,
because with a flattened expansion, we have no easy way to figure out
which PartitionDescs apply to which leaf tables in a multi-level
partition hierarchy.

As it turns out, we end up creating both rte->inh and !rte->inh RTEs
for each intermediate partitioned table, just as we previously did for
the root table.  This seems unnecessary since the partitioned tables
have no storage and are not scanned.  We might want to go back and
rejigger things so that no partitioned tables (including the parent)
need !rte->inh RTEs, but that seems to require some adjustments not
related to the core purpose of this patch.

Ashutosh Bapat, reviewed by me and by Amit Langote.  Some final
adjustments by me.

Discussion: http://postgr.es/m/CAFjFpRd=1venqLL7oGU=C1dEkuvk2DJgvF+7uKbnPHaum1mvHQ@mail.gmail.com

src/backend/optimizer/plan/planner.c

@@ -1038,7 +1038,7 @@ static void
 inheritance_planner(PlannerInfo *root)
 {
 	Query	   *parse = root->parse;
-	int			parentRTindex = parse->resultRelation;
+	int			top_parentRTindex = parse->resultRelation;
 	Bitmapset  *subqueryRTindexes;
 	Bitmapset  *modifiableARIindexes;
 	int			nominalRelation = -1;
@@ -1056,6 +1056,10 @@ inheritance_planner(PlannerInfo *root)
 	Index		rti;
 	RangeTblEntry *parent_rte;
 	List	   *partitioned_rels = NIL;
+	PlannerInfo *parent_root;
+	Query	   *parent_parse;
+	Bitmapset  *parent_relids = bms_make_singleton(top_parentRTindex);
+	PlannerInfo **parent_roots = NULL;
 
 	Assert(parse->commandType != CMD_INSERT);
 
@@ -1119,11 +1123,31 @@ inheritance_planner(PlannerInfo *root)
 	 * (including the root parent) as child members of the inheritance set do
 	 * not appear anywhere else in the plan.  The situation is exactly the
 	 * opposite in the case of non-partitioned inheritance parent as described
-	 * below.
+	 * below. For the same reason, collect the list of descendant partitioned
+	 * tables to be saved in ModifyTable node, so that executor can lock those
+	 * as well.
 	 */
-	parent_rte = rt_fetch(parentRTindex, root->parse->rtable);
+	parent_rte = rt_fetch(top_parentRTindex, root->parse->rtable);
 	if (parent_rte->relkind == RELKIND_PARTITIONED_TABLE)
-		nominalRelation = parentRTindex;
+	{
+		nominalRelation = top_parentRTindex;
+		partitioned_rels = get_partitioned_child_rels(root, top_parentRTindex);
+		/* The root partitioned table is included as a child rel */
+		Assert(list_length(partitioned_rels) >= 1);
+	}
+
+	/*
+	 * The PlannerInfo for each child is obtained by translating the relevant
+	 * members of the PlannerInfo for its immediate parent, which we find
+	 * using the parent_relid in its AppendRelInfo.  We save the PlannerInfo
+	 * for each parent in an array indexed by relid for fast retrieval. Since
+	 * the maximum number of parents is limited by the number of RTEs in the
+	 * query, we use that number to allocate the array. An extra entry is
+	 * needed since relids start from 1.
+	 */
+	parent_roots = (PlannerInfo **) palloc0((list_length(parse->rtable) + 1) *
+											sizeof(PlannerInfo *));
+	parent_roots[top_parentRTindex] = root;
 
 	/*
 	 * And now we can get on with generating a plan for each child table.
@@ -1137,15 +1161,24 @@ inheritance_planner(PlannerInfo *root)
 		Path	   *subpath;
 
 		/* append_rel_list contains all append rels; ignore others */
-		if (appinfo->parent_relid != parentRTindex)
+		if (!bms_is_member(appinfo->parent_relid, parent_relids))
 			continue;
 
+		/*
+		 * expand_inherited_rtentry() always processes a parent before any of
+		 * that parent's children, so the parent_root for this relation should
+		 * already be available.
+		 */
+		parent_root = parent_roots[appinfo->parent_relid];
+		Assert(parent_root != NULL);
+		parent_parse = parent_root->parse;
+
 		/*
 		 * We need a working copy of the PlannerInfo so that we can control
 		 * propagation of information back to the main copy.
 		 */
 		subroot = makeNode(PlannerInfo);
-		memcpy(subroot, root, sizeof(PlannerInfo));
+		memcpy(subroot, parent_root, sizeof(PlannerInfo));
 
 		/*
 		 * Generate modified query with this rel as target.  We first apply
@@ -1154,15 +1187,15 @@ inheritance_planner(PlannerInfo *root)
 		 * then fool around with subquery RTEs.
 		 */
 		subroot->parse = (Query *)
-			adjust_appendrel_attrs(root,
-								   (Node *) parse,
+			adjust_appendrel_attrs(parent_root,
+								   (Node *) parent_parse,
 								   1, &appinfo);
 
 		/*
 		 * If there are securityQuals attached to the parent, move them to the
 		 * child rel (they've already been transformed properly for that).
 		 */
-		parent_rte = rt_fetch(parentRTindex, subroot->parse->rtable);
+		parent_rte = rt_fetch(appinfo->parent_relid, subroot->parse->rtable);
 		child_rte = rt_fetch(appinfo->child_relid, subroot->parse->rtable);
 		child_rte->securityQuals = parent_rte->securityQuals;
 		parent_rte->securityQuals = NIL;
@@ -1173,7 +1206,7 @@ inheritance_planner(PlannerInfo *root)
 		 * executor doesn't need to see the modified copies --- we can just
 		 * pass it the original rowMarks list.)
 		 */
-		subroot->rowMarks = copyObject(root->rowMarks);
+		subroot->rowMarks = copyObject(parent_root->rowMarks);
 
 		/*
 		 * The append_rel_list likewise might contain references to subquery
@@ -1190,7 +1223,7 @@ inheritance_planner(PlannerInfo *root)
 			ListCell   *lc2;
 
 			subroot->append_rel_list = NIL;
-			foreach(lc2, root->append_rel_list)
+			foreach(lc2, parent_root->append_rel_list)
 			{
 				AppendRelInfo *appinfo2 = lfirst_node(AppendRelInfo, lc2);
 
@@ -1225,7 +1258,7 @@ inheritance_planner(PlannerInfo *root)
 			ListCell   *lr;
 
 			rti = 1;
-			foreach(lr, parse->rtable)
+			foreach(lr, parent_parse->rtable)
 			{
 				RangeTblEntry *rte = lfirst_node(RangeTblEntry, lr);
 
@@ -1272,6 +1305,22 @@ inheritance_planner(PlannerInfo *root)
 		/* hack to mark target relation as an inheritance partition */
 		subroot->hasInheritedTarget = true;
 
+		/*
+		 * If the child is further partitioned, remember it as a parent. Since
+		 * a partitioned table does not have any data, we don't need to create
+		 * a plan for it. We do, however, need to remember the PlannerInfo for
+		 * use when processing its children.
+		 */
+		if (child_rte->inh)
+		{
+			Assert(child_rte->relkind == RELKIND_PARTITIONED_TABLE);
+			parent_relids =
+				bms_add_member(parent_relids, appinfo->child_relid);
+			parent_roots[appinfo->child_relid] = subroot;
+
+			continue;
+		}
+
 		/* Generate Path(s) for accessing this result relation */
 		grouping_planner(subroot, true, 0.0 /* retrieve all tuples */ );
 
@@ -1368,13 +1417,6 @@ inheritance_planner(PlannerInfo *root)
 		Assert(!parse->onConflict);
 	}
 
-	if (parent_rte->relkind == RELKIND_PARTITIONED_TABLE)
-	{
-		partitioned_rels = get_partitioned_child_rels(root, parentRTindex);
-		/* The root partitioned table is included as a child rel */
-		Assert(list_length(partitioned_rels) >= 1);
-	}
-
 	/* Result path must go into outer query's FINAL upperrel */
 	final_rel = fetch_upper_rel(root, UPPERREL_FINAL, NULL);