Rename PathKeyInfo to GroupByOrdering

0452b461bc made optimizer explore alternative orderings of group-by pathkeys.
The PathKeyInfo data structure was used to store the particular ordering of
group-by pathkeys and corresponding clauses.  It turns out that PathKeyInfo
is not the best name for that purpose.  This commit renames this data structure
to GroupByOrdering, and revises its comment.

Discussion: https://postgr.es/m/db0fc3a4-966c-4cec-a136-94024d39212d%40postgrespro.ru
Reported-by: Tom Lane
Author: Andrei Lepikhov
Reviewed-by: Alexander Korotkov, Pavel Borisov

src/backend/optimizer/path/pathkeys.c

@@ -450,7 +450,7 @@ group_keys_reorder_by_pathkeys(List *pathkeys, List **group_pathkeys,
 /*
  * pathkeys_are_duplicate
  *		Check if give pathkeys are already contained the list of
- *		PathKeyInfo's.
+ *		GroupByOrdering's.
  */
 static bool
 pathkeys_are_duplicate(List *infos, List *pathkeys)
@@ -459,7 +459,7 @@ pathkeys_are_duplicate(List *infos, List *pathkeys)
 
 	foreach(lc, infos)
 	{
-		PathKeyInfo *info = lfirst_node(PathKeyInfo, lc);
+		GroupByOrdering *info = lfirst_node(GroupByOrdering, lc);
 
 		if (compare_pathkeys(pathkeys, info->pathkeys) == PATHKEYS_EQUAL)
 			return true;
@@ -471,7 +471,7 @@ pathkeys_are_duplicate(List *infos, List *pathkeys)
  * get_useful_group_keys_orderings
  *		Determine which orderings of GROUP BY keys are potentially interesting.
  *
- * Returns a list of PathKeyInfo items, each representing an interesting
+ * Returns a list of GroupByOrdering items, each representing an interesting
  * ordering of GROUP BY keys.  Each item stores pathkeys and clauses in the
  * matching order.
  *
@@ -486,13 +486,13 @@ get_useful_group_keys_orderings(PlannerInfo *root, Path *path)
 {
 	Query	   *parse = root->parse;
 	List	   *infos = NIL;
-	PathKeyInfo *info;
+	GroupByOrdering *info;
 
 	List	   *pathkeys = root->group_pathkeys;
 	List	   *clauses = root->processed_groupClause;
 
 	/* always return at least the original pathkeys/clauses */
-	info = makeNode(PathKeyInfo);
+	info = makeNode(GroupByOrdering);
 	info->pathkeys = pathkeys;
 	info->clauses = clauses;
 	infos = lappend(infos, info);
@@ -528,7 +528,7 @@ get_useful_group_keys_orderings(PlannerInfo *root, Path *path)
 			(enable_incremental_sort || n == root->num_groupby_pathkeys) &&
 			!pathkeys_are_duplicate(infos, pathkeys))
 		{
-			info = makeNode(PathKeyInfo);
+			info = makeNode(GroupByOrdering);
 			info->pathkeys = pathkeys;
 			info->clauses = clauses;
 
@@ -553,7 +553,7 @@ get_useful_group_keys_orderings(PlannerInfo *root, Path *path)
 			(enable_incremental_sort || n == list_length(root->sort_pathkeys)) &&
 			!pathkeys_are_duplicate(infos, pathkeys))
 		{
-			info = makeNode(PathKeyInfo);
+			info = makeNode(GroupByOrdering);
 			info->pathkeys = pathkeys;
 			info->clauses = clauses;
 
@@ -563,7 +563,7 @@ get_useful_group_keys_orderings(PlannerInfo *root, Path *path)
 
 #ifdef USE_ASSERT_CHECKING
 	{
-		PathKeyInfo *pinfo = linitial_node(PathKeyInfo, infos);
+		GroupByOrdering *pinfo = linitial_node(GroupByOrdering, infos);
 		ListCell   *lc;
 
 		/* Test consistency of info structures */
@@ -572,7 +572,7 @@ get_useful_group_keys_orderings(PlannerInfo *root, Path *path)
 			ListCell   *lc1,
 					   *lc2;
 
-			info = lfirst_node(PathKeyInfo, lc);
+			info = lfirst_node(GroupByOrdering, lc);
 
 			Assert(list_length(info->clauses) == list_length(pinfo->clauses));
 			Assert(list_length(info->pathkeys) == list_length(pinfo->pathkeys));

src/backend/optimizer/plan/planner.c

@@ -6917,7 +6917,7 @@ add_paths_to_grouping_rel(PlannerInfo *root, RelOptInfo *input_rel,
 
 			foreach(lc2, pathkey_orderings)
 			{
-				PathKeyInfo *info = (PathKeyInfo *) lfirst(lc2);
+				GroupByOrdering *info = (GroupByOrdering *) lfirst(lc2);
 
 				/* restore the path (we replace it in the loop) */
 				path = path_save;
@@ -6998,7 +6998,7 @@ add_paths_to_grouping_rel(PlannerInfo *root, RelOptInfo *input_rel,
 				/* process all potentially interesting grouping reorderings */
 				foreach(lc2, pathkey_orderings)
 				{
-					PathKeyInfo *info = (PathKeyInfo *) lfirst(lc2);
+					GroupByOrdering *info = (GroupByOrdering *) lfirst(lc2);
 
 					/* restore the path (we replace it in the loop) */
 					path = path_save;
@@ -7249,7 +7249,7 @@ create_partial_grouping_paths(PlannerInfo *root,
 			/* process all potentially interesting grouping reorderings */
 			foreach(lc2, pathkey_orderings)
 			{
-				PathKeyInfo *info = (PathKeyInfo *) lfirst(lc2);
+				GroupByOrdering *info = (GroupByOrdering *) lfirst(lc2);
 
 				/* restore the path (we replace it in the loop) */
 				path = path_save;
@@ -7305,7 +7305,7 @@ create_partial_grouping_paths(PlannerInfo *root,
 			/* process all potentially interesting grouping reorderings */
 			foreach(lc2, pathkey_orderings)
 			{
-				PathKeyInfo *info = (PathKeyInfo *) lfirst(lc2);
+				GroupByOrdering *info = (GroupByOrdering *) lfirst(lc2);
 
 
 				/* restore the path (we replace it in the loop) */

src/include/nodes/pathnodes.h

@@ -1468,14 +1468,21 @@ typedef struct PathKey
 } PathKey;
 
 /*
- * Combines the information about pathkeys and the associated clauses.
+ * Contains an order of group-by clauses and the corresponding list of
+ * pathkeys.
+ *
+ * The elements of 'clauses' list should have the same order as the head of
+ * 'pathkeys' list.  The tleSortGroupRef of the clause should be equal to
+ * ec_sortref of the pathkey equivalence class.  If there are redundant
+ * clauses with the same tleSortGroupRef, they must be grouped together.
  */
-typedef struct PathKeyInfo
+typedef struct GroupByOrdering
 {
 	NodeTag		type;
+
 	List	   *pathkeys;
 	List	   *clauses;
-} PathKeyInfo;
+} GroupByOrdering;
 
 /*
  * VolatileFunctionStatus -- allows nodes to cache their

src/tools/pgindent/typedefs.list

@@ -1056,6 +1056,7 @@ GrantRoleStmt
 GrantStmt
 GrantTargetType
 Group
+GroupByOrdering
 GroupClause
 GroupPath
 GroupPathExtraData
@@ -2067,7 +2068,6 @@ PathClauseUsage
 PathCostComparison
 PathHashStack
 PathKey
-PathKeyInfo
 PathKeysComparison
 PathTarget
 PatternInfo