Small improvements to OPTIMIZER_DEBUG code.

Now that Paths have their own rows field, print that rather than
the parent relation's rowcount.

Show the relid sets associated with Paths using table names rather
than numbers; since this code is able to print simple Var references
using table names, it seems a bit silly that print_relids can't.

Print the cheapest_parameterized_paths list for a RelOptInfo, and
include information about a parameterized path's required_outer rels.

Noted while trying to use this feature to debug Alexander Kirkouski's
recent bug report.

src/backend/optimizer/path/allpaths.c

@@ -2829,7 +2829,7 @@ remove_unused_subquery_outputs(Query *subquery, RelOptInfo *rel)
 #ifdef OPTIMIZER_DEBUG
 
 static void
-print_relids(Relids relids)
+print_relids(PlannerInfo *root, Relids relids)
 {
 	int			x;
 	bool		first = true;
@@ -2839,7 +2839,11 @@ print_relids(Relids relids)
 	{
 		if (!first)
 			printf(" ");
-		printf("%d", x);
+		if (x < root->simple_rel_array_size &&
+			root->simple_rte_array[x])
+			printf("%s", root->simple_rte_array[x]->eref->aliasname);
+		else
+			printf("%d", x);
 		first = false;
 	}
 }
@@ -3013,10 +3017,17 @@ print_path(PlannerInfo *root, Path *path, int indent)
 	if (path->parent)
 	{
 		printf("(");
-		print_relids(path->parent->relids);
-		printf(") rows=%.0f", path->parent->rows);
+		print_relids(root, path->parent->relids);
+		printf(")");
+	}
+	if (path->param_info)
+	{
+		printf(" required_outer (");
+		print_relids(root, path->param_info->ppi_req_outer);
+		printf(")");
 	}
-	printf(" cost=%.2f..%.2f\n", path->startup_cost, path->total_cost);
+	printf(" rows=%.0f cost=%.2f..%.2f\n",
+		   path->rows, path->startup_cost, path->total_cost);
 
 	if (path->pathkeys)
 	{
@@ -3062,7 +3073,7 @@ debug_print_rel(PlannerInfo *root, RelOptInfo *rel)
 	ListCell   *l;
 
 	printf("RELOPTINFO (");
-	print_relids(rel->relids);
+	print_relids(root, rel->relids);
 	printf("): rows=%.0f width=%d\n", rel->rows, rel->reltarget->width);
 
 	if (rel->baserestrictinfo)
@@ -3082,6 +3093,12 @@ debug_print_rel(PlannerInfo *root, RelOptInfo *rel)
 	printf("\tpath list:\n");
 	foreach(l, rel->pathlist)
 		print_path(root, lfirst(l), 1);
+	if (rel->cheapest_parameterized_paths)
+	{
+		printf("\n\tcheapest parameterized paths:\n");
+		foreach(l, rel->cheapest_parameterized_paths)
+			print_path(root, lfirst(l), 1);
+	}
 	if (rel->cheapest_startup_path)
 	{
 		printf("\n\tcheapest startup path:\n");