Revert pre 5bf748b SAOP behavior in PG17

Commit 5bf748b allows generation of unsafe SAOP path keys
on a multicolumn index that were disabled previously by 807a40c.

src/backend/optimizer/path/indxpath.c

@@ -98,7 +98,8 @@ static List *build_index_paths(PlannerInfo *root, RelOptInfo *rel,
 							   IndexOptInfo *index, IndexClauseSet *clauses,
 							   bool useful_predicate,
 							   ScanTypeControl scantype,
-							   bool *skip_nonnative_saop);
+							   bool *skip_nonnative_saop,
+							   bool *skip_lower_saop);
 static List *build_paths_for_OR(PlannerInfo *root, RelOptInfo *rel,
 								List *clauses, List *other_clauses);
 static List *generate_bitmap_or_paths(PlannerInfo *root, RelOptInfo *rel,
@@ -702,6 +703,7 @@ get_index_paths(PlannerInfo *root, RelOptInfo *rel,
 {
 	List	   *indexpaths;
 	bool		skip_nonnative_saop = false;
+	bool            skip_lower_saop = false;
 	ListCell   *lc;
 
 	/*
@@ -712,8 +714,24 @@ get_index_paths(PlannerInfo *root, RelOptInfo *rel,
 								   index, clauses,
 								   index->predOK,
 								   ST_ANYSCAN,
-								   &skip_nonnative_saop);
-
+								   &skip_nonnative_saop,
+								   &skip_lower_saop);
+
+	 /*
+	  * If we skipped any lower-order ScalarArrayOpExprs on an index with an AM
+	  * that supports them, then try again including those clauses.  This will
+	  * produce paths with more selectivity but no ordering.
+	  */
+	if (skip_lower_saop)
+	{
+		indexpaths = list_concat(indexpaths,
+					build_index_paths(root, rel,
+						index, clauses,
+						index->predOK,
+						ST_ANYSCAN,
+						&skip_nonnative_saop,
+						NULL));
+	}
 	/*
 	 * Submit all the ones that can form plain IndexScan plans to add_path. (A
 	 * plain IndexPath can represent either a plain IndexScan or an
@@ -750,6 +768,7 @@ get_index_paths(PlannerInfo *root, RelOptInfo *rel,
 									   index, clauses,
 									   false,
 									   ST_BITMAPSCAN,
+									   NULL,
 									   NULL);
 		*bitindexpaths = list_concat(*bitindexpaths, indexpaths);
 	}
@@ -794,7 +813,8 @@ build_index_paths(PlannerInfo *root, RelOptInfo *rel,
 				  IndexOptInfo *index, IndexClauseSet *clauses,
 				  bool useful_predicate,
 				  ScanTypeControl scantype,
-				  bool *skip_nonnative_saop)
+				  bool *skip_nonnative_saop,
+				  bool *skip_lower_saop)
 {
 	List	   *result = NIL;
 	IndexPath  *ipath;
@@ -805,6 +825,7 @@ build_index_paths(PlannerInfo *root, RelOptInfo *rel,
 	List	   *orderbyclausecols;
 	List	   *index_pathkeys;
 	List	   *useful_pathkeys;
+	bool            found_lower_saop_clause;
 	bool		pathkeys_possibly_useful;
 	bool		index_is_ordered;
 	bool		index_only_scan;
@@ -843,6 +864,7 @@ build_index_paths(PlannerInfo *root, RelOptInfo *rel,
 	 * otherwise accounted for.
 	 */
 	index_clauses = NIL;
+	found_lower_saop_clause = false;
 	outer_relids = bms_copy(rel->lateral_relids);
 	for (indexcol = 0; indexcol < index->nkeycolumns; indexcol++)
 	{
@@ -866,6 +888,16 @@ build_index_paths(PlannerInfo *root, RelOptInfo *rel,
 				*skip_nonnative_saop = true;
 				continue;
 			}
+			if (skip_nonnative_saop && IsA(rinfo->clause, ScalarArrayOpExpr) && indexcol > 0)
+			{
+				if (skip_lower_saop)
+				{
+					/* Caller doesn't want to lose index ordering */
+					*skip_lower_saop = true;
+					continue;
+				}
+			found_lower_saop_clause = true;
+			}
 
 			/* OK to include this clause */
 			index_clauses = lappend(index_clauses, iclause);
@@ -897,6 +929,7 @@ build_index_paths(PlannerInfo *root, RelOptInfo *rel,
 	 * if we are only trying to build bitmap indexscans.
 	 */
 	pathkeys_possibly_useful = (scantype != ST_BITMAPSCAN &&
+								!found_lower_saop_clause &&
 								has_useful_pathkeys(root, rel));
 	index_is_ordered = (index->sortopfamily != NULL);
 	if (index_is_ordered && pathkeys_possibly_useful)
@@ -1148,6 +1181,7 @@ build_paths_for_OR(PlannerInfo *root, RelOptInfo *rel,
 									   index, &clauseset,
 									   useful_predicate,
 									   ST_BITMAPSCAN,
+									   NULL,
 									   NULL);
 		result = list_concat(result, indexpaths);
 	}

src/test/regress/expected/create_index.out

@@ -1943,11 +1943,13 @@ explain (costs off)
 SELECT thousand, tenthous FROM tenk1
 WHERE thousand < 2 AND tenthous IN (1001,3000)
 ORDER BY thousand;
-                                   QUERY PLAN                                   
---------------------------------------------------------------------------------
- Index Only Scan using tenk1_thous_tenthous on tenk1
-   Index Cond: ((thousand < 2) AND (tenthous = ANY ('{1001,3000}'::integer[])))
-(2 rows)
+                                      QUERY PLAN                                      
+--------------------------------------------------------------------------------------
+ Sort
+   Sort Key: thousand
+   ->  Index Only Scan using tenk1_thous_tenthous on tenk1
+         Index Cond: ((thousand < 2) AND (tenthous = ANY ('{1001,3000}'::integer[])))
+(4 rows)
 
 SELECT thousand, tenthous FROM tenk1
 WHERE thousand < 2 AND tenthous IN (1001,3000)
@@ -1963,11 +1965,13 @@ explain (costs off)
 SELECT thousand, tenthous FROM tenk1
 WHERE thousand < 2 AND tenthous IN (1001,3000)
 ORDER BY thousand DESC, tenthous DESC;
-                                   QUERY PLAN                                   
---------------------------------------------------------------------------------
- Index Only Scan Backward using tenk1_thous_tenthous on tenk1
-   Index Cond: ((thousand < 2) AND (tenthous = ANY ('{1001,3000}'::integer[])))
-(2 rows)
+                                      QUERY PLAN                                      
+--------------------------------------------------------------------------------------
+ Sort
+   Sort Key: thousand DESC, tenthous DESC
+   ->  Index Only Scan using tenk1_thous_tenthous on tenk1
+         Index Cond: ((thousand < 2) AND (tenthous = ANY ('{1001,3000}'::integer[])))
+(4 rows)
 
 SELECT thousand, tenthous FROM tenk1
 WHERE thousand < 2 AND tenthous IN (1001,3000)