Rethink representation of PathTargets.

In commit 19a54114 I did not make PathTarget a subtype of Node,
and embedded a RelOptInfo's reltarget directly into it rather than having
a separately-allocated Node.  In hindsight that was misguided
micro-optimization, enabled by the fact that at that point we didn't have
any Paths with custom PathTargets.  Now that PathTarget processing has
been fleshed out some more, it's easier to see that it's better to have
PathTarget as an indepedent Node type, even if it does cost us one more
palloc to create a RelOptInfo.  So change it while we still can.

This commit just changes the representation, without doing anything more
interesting than that.

contrib/file_fdw/file_fdw.c

@@ -821,7 +821,7 @@ check_selective_binary_conversion(RelOptInfo *baserel,
 	}
 
 	/* Collect all the attributes needed for joins or final output. */
-	pull_varattnos((Node *) baserel->reltarget.exprs, baserel->relid,
+	pull_varattnos((Node *) baserel->reltarget->exprs, baserel->relid,
 				   &attrs_used);
 
 	/* Add all the attributes used by restriction clauses. */
@@ -953,7 +953,7 @@ estimate_size(PlannerInfo *root, RelOptInfo *baserel,
 		 */
 		int			tuple_width;
 
-		tuple_width = MAXALIGN(baserel->reltarget.width) +
+		tuple_width = MAXALIGN(baserel->reltarget->width) +
 			MAXALIGN(SizeofHeapTupleHeader);
 		ntuples = clamp_row_est((double) stat_buf.st_size /
 								(double) tuple_width);

contrib/postgres_fdw/deparse.c

@@ -728,10 +728,10 @@ build_tlist_to_deparse(RelOptInfo *foreignrel)
 	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
 
 	/*
-	 * We require columns specified in foreignrel->reltarget.exprs and those
+	 * We require columns specified in foreignrel->reltarget->exprs and those
 	 * required for evaluating the local conditions.
 	 */
-	tlist = add_to_flat_tlist(tlist, foreignrel->reltarget.exprs);
+	tlist = add_to_flat_tlist(tlist, foreignrel->reltarget->exprs);
 	tlist = add_to_flat_tlist(tlist,
 							  pull_var_clause((Node *) fpinfo->local_conds,
 											  PVC_RECURSE_PLACEHOLDERS));

contrib/postgres_fdw/postgres_fdw.c

@@ -481,7 +481,7 @@ postgresGetForeignRelSize(PlannerInfo *root,
 	 * columns used in them.  Doesn't seem worth detecting that case though.)
 	 */
 	fpinfo->attrs_used = NULL;
-	pull_varattnos((Node *) baserel->reltarget.exprs, baserel->relid,
+	pull_varattnos((Node *) baserel->reltarget->exprs, baserel->relid,
 				   &fpinfo->attrs_used);
 	foreach(lc, fpinfo->local_conds)
 	{
@@ -532,7 +532,7 @@ postgresGetForeignRelSize(PlannerInfo *root,
 
 		/* Report estimated baserel size to planner. */
 		baserel->rows = fpinfo->rows;
-		baserel->reltarget.width = fpinfo->width;
+		baserel->reltarget->width = fpinfo->width;
 	}
 	else
 	{
@@ -549,7 +549,7 @@ postgresGetForeignRelSize(PlannerInfo *root,
 		{
 			baserel->pages = 10;
 			baserel->tuples =
-				(10 * BLCKSZ) / (baserel->reltarget.width +
+				(10 * BLCKSZ) / (baserel->reltarget->width +
 								 MAXALIGN(SizeofHeapTupleHeader));
 		}
 
@@ -2164,7 +2164,7 @@ estimate_path_cost_size(PlannerInfo *root,
 		 * between foreign relations.
 		 */
 		rows = foreignrel->rows;
-		width = foreignrel->reltarget.width;
+		width = foreignrel->reltarget->width;
 
 		/* Back into an estimate of the number of retrieved rows. */
 		retrieved_rows = clamp_row_est(rows / fpinfo->local_conds_sel);
@@ -3690,7 +3690,7 @@ postgresGetForeignJoinPaths(PlannerInfo *root,
 							&width, &startup_cost, &total_cost);
 	/* Now update this information in the joinrel */
 	joinrel->rows = rows;
-	joinrel->reltarget.width = width;
+	joinrel->reltarget->width = width;
 	fpinfo->rows = rows;
 	fpinfo->width = width;
 	fpinfo->startup_cost = startup_cost;

doc/src/sgml/fdwhandler.sgml

@@ -1173,7 +1173,7 @@ GetForeignServerByName(const char *name, bool missing_ok);
      it contains restriction quals (<literal>WHERE</> clauses) that should be
      used to filter the rows to be fetched.  (The FDW itself is not required
      to enforce these quals, as the core executor can check them instead.)
-     <literal>baserel-&gt;reltarget.exprs</> can be used to determine which
+     <literal>baserel-&gt;reltarget-&gt;exprs</> can be used to determine which
      columns need to be fetched; but note that it only lists columns that
      have to be emitted by the <structname>ForeignScan</> plan node, not
      columns that are used in qual evaluation but not output by the query.

src/backend/nodes/outfuncs.c

@@ -1598,22 +1598,8 @@ _outPathInfo(StringInfo str, const Path *node)
 	WRITE_ENUM_FIELD(pathtype, NodeTag);
 	appendStringInfoString(str, " :parent_relids ");
 	_outBitmapset(str, node->parent->relids);
-	if (node->pathtarget != &(node->parent->reltarget))
-	{
-		WRITE_NODE_FIELD(pathtarget->exprs);
-		if (node->pathtarget->sortgrouprefs)
-		{
-			int			i;
-
-			appendStringInfoString(str, " :pathtarget->sortgrouprefs");
-			for (i = 0; i < list_length(node->pathtarget->exprs); i++)
-				appendStringInfo(str, " %u",
-								 node->pathtarget->sortgrouprefs[i]);
-		}
-		WRITE_FLOAT_FIELD(pathtarget->cost.startup, "%.2f");
-		WRITE_FLOAT_FIELD(pathtarget->cost.per_tuple, "%.2f");
-		WRITE_INT_FIELD(pathtarget->width);
-	}
+	if (node->pathtarget != node->parent->reltarget)
+		WRITE_NODE_FIELD(pathtarget);
 	appendStringInfoString(str, " :required_outer ");
 	if (node->param_info)
 		_outBitmapset(str, node->param_info->ppi_req_outer);
@@ -2094,11 +2080,7 @@ _outRelOptInfo(StringInfo str, const RelOptInfo *node)
 	WRITE_BOOL_FIELD(consider_startup);
 	WRITE_BOOL_FIELD(consider_param_startup);
 	WRITE_BOOL_FIELD(consider_parallel);
-	WRITE_NODE_FIELD(reltarget.exprs);
-	/* reltarget.sortgrouprefs is never interesting, at present anyway */
-	WRITE_FLOAT_FIELD(reltarget.cost.startup, "%.2f");
-	WRITE_FLOAT_FIELD(reltarget.cost.per_tuple, "%.2f");
-	WRITE_INT_FIELD(reltarget.width);
+	WRITE_NODE_FIELD(reltarget);
 	WRITE_NODE_FIELD(pathlist);
 	WRITE_NODE_FIELD(ppilist);
 	WRITE_NODE_FIELD(partial_pathlist);
@@ -2201,6 +2183,25 @@ _outPathKey(StringInfo str, const PathKey *node)
 	WRITE_BOOL_FIELD(pk_nulls_first);
 }
 
+static void
+_outPathTarget(StringInfo str, const PathTarget *node)
+{
+	WRITE_NODE_TYPE("PATHTARGET");
+
+	WRITE_NODE_FIELD(exprs);
+	if (node->sortgrouprefs)
+	{
+		int			i;
+
+		appendStringInfoString(str, " :sortgrouprefs");
+		for (i = 0; i < list_length(node->exprs); i++)
+			appendStringInfo(str, " %u", node->sortgrouprefs[i]);
+	}
+	WRITE_FLOAT_FIELD(cost.startup, "%.2f");
+	WRITE_FLOAT_FIELD(cost.per_tuple, "%.2f");
+	WRITE_INT_FIELD(width);
+}
+
 static void
 _outParamPathInfo(StringInfo str, const ParamPathInfo *node)
 {
@@ -3612,6 +3613,9 @@ _outNode(StringInfo str, const void *obj)
 			case T_PathKey:
 				_outPathKey(str, obj);
 				break;
+			case T_PathTarget:
+				_outPathTarget(str, obj);
+				break;
 			case T_ParamPathInfo:
 				_outParamPathInfo(str, obj);
 				break;

src/backend/optimizer/path/allpaths.c

@@ -936,7 +936,7 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
 		/*
 		 * CE failed, so finish copying/modifying targetlist and join quals.
 		 *
-		 * Note: the resulting childrel->reltarget.exprs may contain arbitrary
+		 * NB: the resulting childrel->reltarget->exprs may contain arbitrary
 		 * expressions, which otherwise would not occur in a rel's targetlist.
 		 * Code that might be looking at an appendrel child must cope with
 		 * such.  (Normally, a rel's targetlist would only include Vars and
@@ -947,9 +947,9 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
 			adjust_appendrel_attrs(root,
 								   (Node *) rel->joininfo,
 								   appinfo);
-		childrel->reltarget.exprs = (List *)
+		childrel->reltarget->exprs = (List *)
 			adjust_appendrel_attrs(root,
-								   (Node *) rel->reltarget.exprs,
+								   (Node *) rel->reltarget->exprs,
 								   appinfo);
 
 		/*
@@ -994,7 +994,7 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
 		Assert(childrel->rows > 0);
 
 		parent_rows += childrel->rows;
-		parent_size += childrel->reltarget.width * childrel->rows;
+		parent_size += childrel->reltarget->width * childrel->rows;
 
 		/*
 		 * Accumulate per-column estimates too.  We need not do anything for
@@ -1004,8 +1004,8 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
 		 *
 		 * By construction, child's targetlist is 1-to-1 with parent's.
 		 */
-		forboth(parentvars, rel->reltarget.exprs,
-				childvars, childrel->reltarget.exprs)
+		forboth(parentvars, rel->reltarget->exprs,
+				childvars, childrel->reltarget->exprs)
 		{
 			Var		   *parentvar = (Var *) lfirst(parentvars);
 			Node	   *childvar = (Node *) lfirst(childvars);
@@ -1040,7 +1040,7 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
 
 		Assert(parent_rows > 0);
 		rel->rows = parent_rows;
-		rel->reltarget.width = rint(parent_size / parent_rows);
+		rel->reltarget->width = rint(parent_size / parent_rows);
 		for (i = 0; i < nattrs; i++)
 			rel->attr_widths[i] = rint(parent_attrsizes[i] / parent_rows);
 
@@ -1515,7 +1515,7 @@ set_dummy_rel_pathlist(RelOptInfo *rel)
 {
 	/* Set dummy size estimates --- we leave attr_widths[] as zeroes */
 	rel->rows = 0;
-	rel->reltarget.width = 0;
+	rel->reltarget->width = 0;
 
 	/* Discard any pre-existing paths; no further need for them */
 	rel->pathlist = NIL;
@@ -1771,7 +1771,7 @@ set_function_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
 		 * not reference the ordinality column, or at least not in any way
 		 * that would be interesting for sorting.
 		 */
-		foreach(lc, rel->reltarget.exprs)
+		foreach(lc, rel->reltarget->exprs)
 		{
 			Var		   *node = (Var *) lfirst(lc);
 
@@ -2717,7 +2717,7 @@ remove_unused_subquery_outputs(Query *subquery, RelOptInfo *rel)
 	 * isn't computed for inheritance child rels, cf set_append_rel_size().
 	 * (XXX might be worth changing that sometime.)
 	 */
-	pull_varattnos((Node *) rel->reltarget.exprs, rel->relid, &attrs_used);
+	pull_varattnos((Node *) rel->reltarget->exprs, rel->relid, &attrs_used);
 
 	/* Add all the attributes used by un-pushed-down restriction clauses. */
 	foreach(lc, rel->baserestrictinfo)
@@ -3028,7 +3028,7 @@ debug_print_rel(PlannerInfo *root, RelOptInfo *rel)
 
 	printf("RELOPTINFO (");
 	print_relids(rel->relids);
-	printf("): rows=%.0f width=%d\n", rel->rows, rel->reltarget.width);
+	printf("): rows=%.0f width=%d\n", rel->rows, rel->reltarget->width);
 
 	if (rel->baserestrictinfo)
 	{

src/backend/optimizer/path/costsize.c

@@ -4218,7 +4218,7 @@ set_foreign_size_estimates(PlannerInfo *root, RelOptInfo *rel)
  * that have to be calculated at this relation.  This is the amount of data
  * we'd need to pass upwards in case of a sort, hash, etc.
  *
- * This function also sets reltarget.cost, so it's a bit misnamed now.
+ * This function also sets reltarget->cost, so it's a bit misnamed now.
  *
  * NB: this works best on plain relations because it prefers to look at
  * real Vars.  For subqueries, set_subquery_size_estimates will already have
@@ -4239,10 +4239,10 @@ set_rel_width(PlannerInfo *root, RelOptInfo *rel)
 	ListCell   *lc;
 
 	/* Vars are assumed to have cost zero, but other exprs do not */
-	rel->reltarget.cost.startup = 0;
-	rel->reltarget.cost.per_tuple = 0;
+	rel->reltarget->cost.startup = 0;
+	rel->reltarget->cost.per_tuple = 0;
 
-	foreach(lc, rel->reltarget.exprs)
+	foreach(lc, rel->reltarget->exprs)
 	{
 		Node	   *node = (Node *) lfirst(lc);
 
@@ -4309,7 +4309,7 @@ set_rel_width(PlannerInfo *root, RelOptInfo *rel)
 		{
 			/*
 			 * We will need to evaluate the PHV's contained expression while
-			 * scanning this rel, so be sure to include it in reltarget.cost.
+			 * scanning this rel, so be sure to include it in reltarget->cost.
 			 */
 			PlaceHolderVar *phv = (PlaceHolderVar *) node;
 			PlaceHolderInfo *phinfo = find_placeholder_info(root, phv, false);
@@ -4317,8 +4317,8 @@ set_rel_width(PlannerInfo *root, RelOptInfo *rel)
 
 			tuple_width += phinfo->ph_width;
 			cost_qual_eval_node(&cost, (Node *) phv->phexpr, root);
-			rel->reltarget.cost.startup += cost.startup;
-			rel->reltarget.cost.per_tuple += cost.per_tuple;
+			rel->reltarget->cost.startup += cost.startup;
+			rel->reltarget->cost.per_tuple += cost.per_tuple;
 		}
 		else
 		{
@@ -4335,8 +4335,8 @@ set_rel_width(PlannerInfo *root, RelOptInfo *rel)
 			tuple_width += item_width;
 			/* Not entirely clear if we need to account for cost, but do so */
 			cost_qual_eval_node(&cost, node, root);
-			rel->reltarget.cost.startup += cost.startup;
-			rel->reltarget.cost.per_tuple += cost.per_tuple;
+			rel->reltarget->cost.startup += cost.startup;
+			rel->reltarget->cost.per_tuple += cost.per_tuple;
 		}
 	}
 
@@ -4373,7 +4373,7 @@ set_rel_width(PlannerInfo *root, RelOptInfo *rel)
 	}
 
 	Assert(tuple_width >= 0);
-	rel->reltarget.width = tuple_width;
+	rel->reltarget->width = tuple_width;
 }
 
 /*

src/backend/optimizer/path/indxpath.c

@@ -1550,7 +1550,7 @@ bitmap_scan_cost_est(PlannerInfo *root, RelOptInfo *rel, Path *ipath)
 	bpath.path.type = T_BitmapHeapPath;
 	bpath.path.pathtype = T_BitmapHeapScan;
 	bpath.path.parent = rel;
-	bpath.path.pathtarget = &(rel->reltarget);
+	bpath.path.pathtarget = rel->reltarget;
 	bpath.path.param_info = get_baserel_parampathinfo(root, rel,
 													  required_outer);
 	bpath.path.pathkeys = NIL;
@@ -1579,7 +1579,7 @@ bitmap_and_cost_est(PlannerInfo *root, RelOptInfo *rel, List *paths)
 	apath.path.type = T_BitmapAndPath;
 	apath.path.pathtype = T_BitmapAnd;
 	apath.path.parent = rel;
-	apath.path.pathtarget = &(rel->reltarget);
+	apath.path.pathtarget = rel->reltarget;
 	apath.path.param_info = NULL;		/* not used in bitmap trees */
 	apath.path.pathkeys = NIL;
 	apath.bitmapquals = paths;
@@ -1592,7 +1592,7 @@ bitmap_and_cost_est(PlannerInfo *root, RelOptInfo *rel, List *paths)
 	bpath.path.type = T_BitmapHeapPath;
 	bpath.path.pathtype = T_BitmapHeapScan;
 	bpath.path.parent = rel;
-	bpath.path.pathtarget = &(rel->reltarget);
+	bpath.path.pathtarget = rel->reltarget;
 	bpath.path.param_info = get_baserel_parampathinfo(root, rel,
 													  required_outer);
 	bpath.path.pathkeys = NIL;
@@ -1815,7 +1815,7 @@ check_index_only(RelOptInfo *rel, IndexOptInfo *index)
 	 * look at rel's targetlist, not the attr_needed data, because attr_needed
 	 * isn't computed for inheritance child rels.
 	 */
-	pull_varattnos((Node *) rel->reltarget.exprs, rel->relid, &attrs_used);
+	pull_varattnos((Node *) rel->reltarget->exprs, rel->relid, &attrs_used);
 
 	/* Add all the attributes used by restriction clauses. */
 	foreach(lc, rel->baserestrictinfo)

src/backend/optimizer/plan/createplan.c

@@ -3279,7 +3279,7 @@ create_foreignscan_plan(PlannerInfo *root, ForeignPath *best_path,
 		 * Note: we must look at rel's targetlist, not the attr_needed data,
 		 * because attr_needed isn't computed for inheritance child rels.
 		 */
-		pull_varattnos((Node *) rel->reltarget.exprs, scan_relid, &attrs_used);
+		pull_varattnos((Node *) rel->reltarget->exprs, scan_relid, &attrs_used);
 
 		/* Add all the attributes used by restriction clauses. */
 		foreach(lc, rel->baserestrictinfo)

src/backend/optimizer/plan/initsplan.c

@@ -215,8 +215,8 @@ add_vars_to_targetlist(PlannerInfo *root, List *vars,
 			{
 				/* Variable not yet requested, so add to rel's targetlist */
 				/* XXX is copyObject necessary here? */
-				rel->reltarget.exprs = lappend(rel->reltarget.exprs,
-											   copyObject(var));
+				rel->reltarget->exprs = lappend(rel->reltarget->exprs,
+												copyObject(var));
 				/* reltarget cost and width will be computed later */
 			}
 			rel->attr_needed[attno] = bms_add_members(rel->attr_needed[attno],

src/backend/optimizer/plan/planmain.c

@@ -83,7 +83,7 @@ query_planner(PlannerInfo *root, List *tlist,
 		/* The only path for it is a trivial Result path */
 		add_path(final_rel, (Path *)
 				 create_result_path(root, final_rel,
-									&(final_rel->reltarget),
+									final_rel->reltarget,
 									(List *) parse->jointree->quals));
 
 		/* Select cheapest path (pretty easy in this case...) */

src/backend/optimizer/plan/planner.c

@@ -4534,7 +4534,7 @@ plan_cluster_use_sort(Oid tableOid, Oid indexOid)
 	 * set_baserel_size_estimates, just do a quick hack for rows and width.
 	 */
 	rel->rows = rel->tuples;
-	rel->reltarget.width = get_relation_data_width(tableOid, NULL);
+	rel->reltarget->width = get_relation_data_width(tableOid, NULL);
 
 	root->total_table_pages = rel->pages;
 
@@ -4550,7 +4550,7 @@ plan_cluster_use_sort(Oid tableOid, Oid indexOid)
 	/* Estimate the cost of seq scan + sort */
 	seqScanPath = create_seqscan_path(root, rel, NULL, 0);
 	cost_sort(&seqScanAndSortPath, root, NIL,
-			  seqScanPath->total_cost, rel->tuples, rel->reltarget.width,
+			  seqScanPath->total_cost, rel->tuples, rel->reltarget->width,
 			  comparisonCost, maintenance_work_mem, -1.0);
 
 	/* Estimate the cost of index scan */

src/backend/optimizer/util/pathnode.c

@@ -929,7 +929,7 @@ create_seqscan_path(PlannerInfo *root, RelOptInfo *rel,
 
 	pathnode->pathtype = T_SeqScan;
 	pathnode->parent = rel;
-	pathnode->pathtarget = &(rel->reltarget);
+	pathnode->pathtarget = rel->reltarget;
 	pathnode->param_info = get_baserel_parampathinfo(root, rel,
 													 required_outer);
 	pathnode->parallel_aware = parallel_degree > 0 ? true : false;
@@ -953,7 +953,7 @@ create_samplescan_path(PlannerInfo *root, RelOptInfo *rel, Relids required_outer
 
 	pathnode->pathtype = T_SampleScan;
 	pathnode->parent = rel;
-	pathnode->pathtarget = &(rel->reltarget);
+	pathnode->pathtarget = rel->reltarget;
 	pathnode->param_info = get_baserel_parampathinfo(root, rel,
 													 required_outer);
 	pathnode->parallel_aware = false;
@@ -1010,7 +1010,7 @@ create_index_path(PlannerInfo *root,
 
 	pathnode->path.pathtype = indexonly ? T_IndexOnlyScan : T_IndexScan;
 	pathnode->path.parent = rel;
-	pathnode->path.pathtarget = &(rel->reltarget);
+	pathnode->path.pathtarget = rel->reltarget;
 	pathnode->path.param_info = get_baserel_parampathinfo(root, rel,
 														  required_outer);
 	pathnode->path.parallel_aware = false;
@@ -1059,7 +1059,7 @@ create_bitmap_heap_path(PlannerInfo *root,
 
 	pathnode->path.pathtype = T_BitmapHeapScan;
 	pathnode->path.parent = rel;
-	pathnode->path.pathtarget = &(rel->reltarget);
+	pathnode->path.pathtarget = rel->reltarget;
 	pathnode->path.param_info = get_baserel_parampathinfo(root, rel,
 														  required_outer);
 	pathnode->path.parallel_aware = false;
@@ -1089,7 +1089,7 @@ create_bitmap_and_path(PlannerInfo *root,
 
 	pathnode->path.pathtype = T_BitmapAnd;
 	pathnode->path.parent = rel;
-	pathnode->path.pathtarget = &(rel->reltarget);
+	pathnode->path.pathtarget = rel->reltarget;
 	pathnode->path.param_info = NULL;	/* not used in bitmap trees */
 
 	/*
@@ -1125,7 +1125,7 @@ create_bitmap_or_path(PlannerInfo *root,
 
 	pathnode->path.pathtype = T_BitmapOr;
 	pathnode->path.parent = rel;
-	pathnode->path.pathtarget = &(rel->reltarget);
+	pathnode->path.pathtarget = rel->reltarget;
 	pathnode->path.param_info = NULL;	/* not used in bitmap trees */
 
 	/*
@@ -1160,7 +1160,7 @@ create_tidscan_path(PlannerInfo *root, RelOptInfo *rel, List *tidquals,
 
 	pathnode->path.pathtype = T_TidScan;
 	pathnode->path.parent = rel;
-	pathnode->path.pathtarget = &(rel->reltarget);
+	pathnode->path.pathtarget = rel->reltarget;
 	pathnode->path.param_info = get_baserel_parampathinfo(root, rel,
 														  required_outer);
 	pathnode->path.parallel_aware = false;
@@ -1192,7 +1192,7 @@ create_append_path(RelOptInfo *rel, List *subpaths, Relids required_outer,
 
 	pathnode->path.pathtype = T_Append;
 	pathnode->path.parent = rel;
-	pathnode->path.pathtarget = &(rel->reltarget);
+	pathnode->path.pathtarget = rel->reltarget;
 	pathnode->path.param_info = get_appendrel_parampathinfo(rel,
 															required_outer);
 	pathnode->path.parallel_aware = false;
@@ -1251,7 +1251,7 @@ create_merge_append_path(PlannerInfo *root,
 
 	pathnode->path.pathtype = T_MergeAppend;
 	pathnode->path.parent = rel;
-	pathnode->path.pathtarget = &(rel->reltarget);
+	pathnode->path.pathtarget = rel->reltarget;
 	pathnode->path.param_info = get_appendrel_parampathinfo(rel,
 															required_outer);
 	pathnode->path.parallel_aware = false;
@@ -1375,7 +1375,7 @@ create_material_path(RelOptInfo *rel, Path *subpath)
 
 	pathnode->path.pathtype = T_Material;
 	pathnode->path.parent = rel;
-	pathnode->path.pathtarget = &(rel->reltarget);
+	pathnode->path.pathtarget = rel->reltarget;
 	pathnode->path.param_info = subpath->param_info;
 	pathnode->path.parallel_aware = false;
 	pathnode->path.parallel_safe = rel->consider_parallel &&
@@ -1440,7 +1440,7 @@ create_unique_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
 
 	pathnode->path.pathtype = T_Unique;
 	pathnode->path.parent = rel;
-	pathnode->path.pathtarget = &(rel->reltarget);
+	pathnode->path.pathtarget = rel->reltarget;
 	pathnode->path.param_info = subpath->param_info;
 	pathnode->path.parallel_aware = false;
 	pathnode->path.parallel_safe = rel->consider_parallel &&
@@ -1656,7 +1656,7 @@ create_gather_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
 
 	pathnode->path.pathtype = T_Gather;
 	pathnode->path.parent = rel;
-	pathnode->path.pathtarget = &(rel->reltarget);
+	pathnode->path.pathtarget = rel->reltarget;
 	pathnode->path.param_info = get_baserel_parampathinfo(root, rel,
 														  required_outer);
 	pathnode->path.parallel_aware = false;
@@ -1692,7 +1692,7 @@ create_subqueryscan_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
 
 	pathnode->path.pathtype = T_SubqueryScan;
 	pathnode->path.parent = rel;
-	pathnode->path.pathtarget = &(rel->reltarget);
+	pathnode->path.pathtarget = rel->reltarget;
 	pathnode->path.param_info = get_baserel_parampathinfo(root, rel,
 														  required_outer);
 	pathnode->path.parallel_aware = false;
@@ -1720,7 +1720,7 @@ create_functionscan_path(PlannerInfo *root, RelOptInfo *rel,
 
 	pathnode->pathtype = T_FunctionScan;
 	pathnode->parent = rel;
-	pathnode->pathtarget = &(rel->reltarget);
+	pathnode->pathtarget = rel->reltarget;
 	pathnode->param_info = get_baserel_parampathinfo(root, rel,
 													 required_outer);
 	pathnode->parallel_aware = false;
@@ -1746,7 +1746,7 @@ create_valuesscan_path(PlannerInfo *root, RelOptInfo *rel,
 
 	pathnode->pathtype = T_ValuesScan;
 	pathnode->parent = rel;
-	pathnode->pathtarget = &(rel->reltarget);
+	pathnode->pathtarget = rel->reltarget;
 	pathnode->param_info = get_baserel_parampathinfo(root, rel,
 													 required_outer);
 	pathnode->parallel_aware = false;
@@ -1771,7 +1771,7 @@ create_ctescan_path(PlannerInfo *root, RelOptInfo *rel, Relids required_outer)
 
 	pathnode->pathtype = T_CteScan;
 	pathnode->parent = rel;
-	pathnode->pathtarget = &(rel->reltarget);
+	pathnode->pathtarget = rel->reltarget;
 	pathnode->param_info = get_baserel_parampathinfo(root, rel,
 													 required_outer);
 	pathnode->parallel_aware = false;
@@ -1797,7 +1797,7 @@ create_worktablescan_path(PlannerInfo *root, RelOptInfo *rel,
 
 	pathnode->pathtype = T_WorkTableScan;
 	pathnode->parent = rel;
-	pathnode->pathtarget = &(rel->reltarget);
+	pathnode->pathtarget = rel->reltarget;
 	pathnode->param_info = get_baserel_parampathinfo(root, rel,
 													 required_outer);
 	pathnode->parallel_aware = false;
@@ -1833,7 +1833,7 @@ create_foreignscan_path(PlannerInfo *root, RelOptInfo *rel,
 
 	pathnode->path.pathtype = T_ForeignScan;
 	pathnode->path.parent = rel;
-	pathnode->path.pathtarget = &(rel->reltarget);
+	pathnode->path.pathtarget = rel->reltarget;
 	pathnode->path.param_info = get_baserel_parampathinfo(root, rel,
 														  required_outer);
 	pathnode->path.parallel_aware = false;
@@ -1966,7 +1966,7 @@ create_nestloop_path(PlannerInfo *root,
 
 	pathnode->path.pathtype = T_NestLoop;
 	pathnode->path.parent = joinrel;
-	pathnode->path.pathtarget = &(joinrel->reltarget);
+	pathnode->path.pathtarget = joinrel->reltarget;
 	pathnode->path.param_info =
 		get_joinrel_parampathinfo(root,
 								  joinrel,
@@ -2029,7 +2029,7 @@ create_mergejoin_path(PlannerInfo *root,
 
 	pathnode->jpath.path.pathtype = T_MergeJoin;
 	pathnode->jpath.path.parent = joinrel;
-	pathnode->jpath.path.pathtarget = &(joinrel->reltarget);
+	pathnode->jpath.path.pathtarget = joinrel->reltarget;
 	pathnode->jpath.path.param_info =
 		get_joinrel_parampathinfo(root,
 								  joinrel,
@@ -2091,7 +2091,7 @@ create_hashjoin_path(PlannerInfo *root,
 
 	pathnode->jpath.path.pathtype = T_HashJoin;
 	pathnode->jpath.path.parent = joinrel;
-	pathnode->jpath.path.pathtarget = &(joinrel->reltarget);
+	pathnode->jpath.path.pathtarget = joinrel->reltarget;
 	pathnode->jpath.path.param_info =
 		get_joinrel_parampathinfo(root,
 								  joinrel,
@@ -2876,7 +2876,7 @@ create_modifytable_path(PlannerInfo *root, RelOptInfo *rel,
 	pathnode->path.pathtype = T_ModifyTable;
 	pathnode->path.parent = rel;
 	/* pathtarget is not interesting, just make it minimally valid */
-	pathnode->path.pathtarget = &(rel->reltarget);
+	pathnode->path.pathtarget = rel->reltarget;
 	/* For now, assume we are above any joins, so no parameterization */
 	pathnode->path.param_info = NULL;
 	pathnode->path.parallel_aware = false;

src/backend/optimizer/util/placeholder.c

@@ -391,8 +391,8 @@ add_placeholders_to_base_rels(PlannerInfo *root)
 		{
 			RelOptInfo *rel = find_base_rel(root, varno);
 
-			rel->reltarget.exprs = lappend(rel->reltarget.exprs,
-										   copyObject(phinfo->ph_var));
+			rel->reltarget->exprs = lappend(rel->reltarget->exprs,
+											copyObject(phinfo->ph_var));
 			/* reltarget's cost and width fields will be updated later */
 		}
 	}
@@ -425,9 +425,9 @@ add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel,
 			if (bms_is_subset(phinfo->ph_eval_at, relids))
 			{
 				/* Yup, add it to the output */
-				joinrel->reltarget.exprs = lappend(joinrel->reltarget.exprs,
-												   phinfo->ph_var);
-				joinrel->reltarget.width += phinfo->ph_width;
+				joinrel->reltarget->exprs = lappend(joinrel->reltarget->exprs,
+													phinfo->ph_var);
+				joinrel->reltarget->width += phinfo->ph_width;
 
 				/*
 				 * Charge the cost of evaluating the contained expression if
@@ -447,8 +447,8 @@ add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel,
 
 					cost_qual_eval_node(&cost, (Node *) phinfo->ph_var->phexpr,
 										root);
-					joinrel->reltarget.cost.startup += cost.startup;
-					joinrel->reltarget.cost.per_tuple += cost.per_tuple;
+					joinrel->reltarget->cost.startup += cost.startup;
+					joinrel->reltarget->cost.per_tuple += cost.per_tuple;
 				}
 
 				/* Adjust joinrel's direct_lateral_relids as needed */

src/backend/optimizer/util/relnode.c

@@ -24,6 +24,7 @@
 #include "optimizer/placeholder.h"
 #include "optimizer/plancat.h"
 #include "optimizer/restrictinfo.h"
+#include "optimizer/tlist.h"
 #include "utils/hsearch.h"
 
 
@@ -106,11 +107,7 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
 	rel->consider_startup = (root->tuple_fraction > 0);
 	rel->consider_param_startup = false;		/* might get changed later */
 	rel->consider_parallel = false;		/* might get changed later */
-	rel->reltarget.exprs = NIL;
-	rel->reltarget.sortgrouprefs = NULL;
-	rel->reltarget.cost.startup = 0;
-	rel->reltarget.cost.per_tuple = 0;
-	rel->reltarget.width = 0;
+	rel->reltarget = create_empty_pathtarget();
 	rel->pathlist = NIL;
 	rel->ppilist = NIL;
 	rel->partial_pathlist = NIL;
@@ -393,11 +390,7 @@ build_join_rel(PlannerInfo *root,
 	joinrel->consider_startup = (root->tuple_fraction > 0);
 	joinrel->consider_param_startup = false;
 	joinrel->consider_parallel = false;
-	joinrel->reltarget.exprs = NIL;
-	joinrel->reltarget.sortgrouprefs = NULL;
-	joinrel->reltarget.cost.startup = 0;
-	joinrel->reltarget.cost.per_tuple = 0;
-	joinrel->reltarget.width = 0;
+	joinrel->reltarget = create_empty_pathtarget();
 	joinrel->pathlist = NIL;
 	joinrel->ppilist = NIL;
 	joinrel->partial_pathlist = NIL;
@@ -613,7 +606,7 @@ build_joinrel_tlist(PlannerInfo *root, RelOptInfo *joinrel,
 	Relids		relids = joinrel->relids;
 	ListCell   *vars;
 
-	foreach(vars, input_rel->reltarget.exprs)
+	foreach(vars, input_rel->reltarget->exprs)
 	{
 		Var		   *var = (Var *) lfirst(vars);
 		RelOptInfo *baserel;
@@ -643,9 +636,9 @@ build_joinrel_tlist(PlannerInfo *root, RelOptInfo *joinrel,
 		if (bms_nonempty_difference(baserel->attr_needed[ndx], relids))
 		{
 			/* Yup, add it to the output */
-			joinrel->reltarget.exprs = lappend(joinrel->reltarget.exprs, var);
-			/* Vars have cost zero, so no need to adjust reltarget.cost */
-			joinrel->reltarget.width += baserel->attr_widths[ndx];
+			joinrel->reltarget->exprs = lappend(joinrel->reltarget->exprs, var);
+			/* Vars have cost zero, so no need to adjust reltarget->cost */
+			joinrel->reltarget->width += baserel->attr_widths[ndx];
 		}
 	}
 }
@@ -832,6 +825,7 @@ build_empty_join_rel(PlannerInfo *root)
 	joinrel->relids = NULL;		/* empty set */
 	joinrel->rows = 1;			/* we produce one row for such cases */
 	joinrel->rtekind = RTE_JOIN;
+	joinrel->reltarget = create_empty_pathtarget();
 
 	root->join_rel_list = lappend(root->join_rel_list, joinrel);
 
@@ -882,6 +876,7 @@ fetch_upper_rel(PlannerInfo *root, UpperRelationKind kind, Relids relids)
 	upperrel->consider_startup = (root->tuple_fraction > 0);
 	upperrel->consider_param_startup = false;
 	upperrel->consider_parallel = false;		/* might get changed later */
+	upperrel->reltarget = create_empty_pathtarget();
 	upperrel->pathlist = NIL;
 	upperrel->cheapest_startup_path = NULL;
 	upperrel->cheapest_total_path = NULL;

src/backend/optimizer/util/tlist.c

@@ -546,7 +546,7 @@ grouping_is_hashable(List *groupClause)
 PathTarget *
 make_pathtarget_from_tlist(List *tlist)
 {
-	PathTarget *target = (PathTarget *) palloc0(sizeof(PathTarget));
+	PathTarget *target = makeNode(PathTarget);
 	int			i;
 	ListCell   *lc;
 
@@ -606,7 +606,7 @@ make_tlist_from_pathtarget(PathTarget *target)
 PathTarget *
 copy_pathtarget(PathTarget *src)
 {
-	PathTarget *dst = (PathTarget *) palloc(sizeof(PathTarget));
+	PathTarget *dst = makeNode(PathTarget);
 
 	/* Copy scalar fields */
 	memcpy(dst, src, sizeof(PathTarget));
@@ -631,7 +631,7 @@ PathTarget *
 create_empty_pathtarget(void)
 {
 	/* This is easy, but we don't want callers to hard-wire this ... */
-	return (PathTarget *) palloc0(sizeof(PathTarget));
+	return makeNode(PathTarget);
 }
 
 /*

src/include/nodes/nodes.h

@@ -259,6 +259,7 @@ typedef enum NodeTag
 	T_EquivalenceClass,
 	T_EquivalenceMember,
 	T_PathKey,
+	T_PathTarget,
 	T_RestrictInfo,
 	T_PlaceHolderVar,
 	T_SpecialJoinInfo,

src/include/nodes/relation.h

@@ -61,34 +61,6 @@ typedef struct AggClauseCosts
 	Size		transitionSpace;	/* space for pass-by-ref transition data */
 } AggClauseCosts;
 
-/*
- * This struct contains what we need to know during planning about the
- * targetlist (output columns) that a Path will compute.  Each RelOptInfo
- * includes a default PathTarget, which its individual Paths may merely point
- * to.  However, in some cases a Path may compute outputs different from other
- * Paths, and in that case we make a custom PathTarget struct for it.  For
- * example, an indexscan might return index expressions that would otherwise
- * need to be explicitly calculated.
- *
- * exprs contains bare expressions; they do not have TargetEntry nodes on top,
- * though those will appear in finished Plans.
- *
- * sortgrouprefs[] is an array of the same length as exprs, containing the
- * corresponding sort/group refnos, or zeroes for expressions not referenced
- * by sort/group clauses.  If sortgrouprefs is NULL (which it always is in
- * RelOptInfo.reltarget structs; only upper-level Paths contain this info), we
- * have not identified sort/group columns in this tlist.  This allows us to
- * deal with sort/group refnos when needed with less expense than including
- * TargetEntry nodes in the exprs list.
- */
-typedef struct PathTarget
-{
-	List	   *exprs;			/* list of expressions to be computed */
-	Index	   *sortgrouprefs;	/* corresponding sort/group refnos, or 0 */
-	QualCost	cost;			/* cost of evaluating the expressions */
-	int			width;			/* estimated avg width of result tuples */
-} PathTarget;
-
 /*
  * This enum identifies the different types of "upper" (post-scan/join)
  * relations that we might deal with during planning.
@@ -514,7 +486,7 @@ typedef struct RelOptInfo
 	bool		consider_parallel;		/* consider parallel paths? */
 
 	/* default result targetlist for Paths scanning this relation */
-	PathTarget	reltarget;		/* list of Vars/Exprs, cost, width */
+	struct PathTarget *reltarget;		/* list of Vars/Exprs, cost, width */
 
 	/* materialization information */
 	List	   *pathlist;		/* Path structures */
@@ -765,6 +737,39 @@ typedef struct PathKey
 } PathKey;
 
 
+/*
+ * PathTarget
+ *
+ * This struct contains what we need to know during planning about the
+ * targetlist (output columns) that a Path will compute.  Each RelOptInfo
+ * includes a default PathTarget, which its individual Paths may simply
+ * reference.  However, in some cases a Path may compute outputs different
+ * from other Paths, and in that case we make a custom PathTarget for it.
+ * For example, an indexscan might return index expressions that would
+ * otherwise need to be explicitly calculated.  (Note also that "upper"
+ * relations generally don't have useful default PathTargets.)
+ *
+ * exprs contains bare expressions; they do not have TargetEntry nodes on top,
+ * though those will appear in finished Plans.
+ *
+ * sortgrouprefs[] is an array of the same length as exprs, containing the
+ * corresponding sort/group refnos, or zeroes for expressions not referenced
+ * by sort/group clauses.  If sortgrouprefs is NULL (which it generally is in
+ * RelOptInfo.reltarget targets; only upper-level Paths contain this info),
+ * we have not identified sort/group columns in this tlist.  This allows us to
+ * deal with sort/group refnos when needed with less expense than including
+ * TargetEntry nodes in the exprs list.
+ */
+typedef struct PathTarget
+{
+	NodeTag		type;
+	List	   *exprs;			/* list of expressions to be computed */
+	Index	   *sortgrouprefs;	/* corresponding sort/group refnos, or 0 */
+	QualCost	cost;			/* cost of evaluating the expressions */
+	int			width;			/* estimated avg width of result tuples */
+} PathTarget;
+
+
 /*
  * ParamPathInfo
  *
@@ -802,7 +807,7 @@ typedef struct ParamPathInfo
  * "parent" identifies the relation this Path scans, and "pathtarget"
  * describes the precise set of output columns the Path would compute.
  * In simple cases all Paths for a given rel share the same targetlist,
- * which we represent by having path->pathtarget point to parent->reltarget.
+ * which we represent by having path->pathtarget equal to parent->reltarget.
  *
  * "param_info", if not NULL, links to a ParamPathInfo that identifies outer
  * relation(s) that provide parameter values to each scan of this path.