Correct parallel window function in CASE WHEN.

Previously, we attempted to disable window functions inside CASE WHEN
expressions due to concerns about unstable parallel results. However,
this was a misunderstanding. All expressions from the subquery are Var
columns, not the original expressions.

This issue was uncovered when we fixed the subquery row count
estimation, causing the cost to change in the upper plan.

EXPLAIN(COSTS OFF)
SELECT empno, depname, salary, bonus, depadj, MIN(bonus) OVER (ORDER BY
empno), MAX(depadj) OVER () FROM(
	SELECT *,
		CASE WHEN enroll_date < '2008-01-01' THEN 2008 -
extract(YEAR FROM enroll_date) END * 500 AS bonus,
		CASE WHEN
			AVG(salary) OVER (PARTITION BY depname) < salary
		THEN 200 END AS depadj FROM empsalary
)s;
                                        QUERY PLAN
--------------------------------------------------------------------------
 WindowAgg
   ->  WindowAgg
         Order By: s.empno
         ->  Gather Motion 6:1  (slice1; segments: 6)
               Merge Key: s.empno
               ->  Sort
                     Sort Key: s.empno
                     ->  Subquery Scan on s
                           ->  WindowAgg
                                 Partition By: empsalary.depname
                                 ->  Sort
                                       Sort Key: empsalary.depname
                                       ->  Redistribute Motion 6:6
(slice2; segments: 6)
                                             Hash Key: empsalary.depname
                                             Hash Module: 3
                                             ->  Parallel Seq Scan on
empsalary
 Optimizer: Postgres query optimizer
(17 rows)

Authored-by: Zhang Mingli avamingli@gmail.com

Author: avamingli

src/backend/optimizer/plan/planner.c

@@ -300,12 +300,6 @@ static split_rollup_data *make_new_rollups_for_hash_grouping_set(PlannerInfo *ro
 																 Path *path,
 																 grouping_sets_data *gd);
 
-static bool
-contain_case_expr(Node *clause);
-
-static bool
-contain_case_expr_walker(Node *node, void *context);
-
 static void create_partial_window_path(PlannerInfo *root,
 											RelOptInfo *window_rel,
 											Path *path,
@@ -9139,25 +9133,6 @@ make_new_rollups_for_hash_grouping_set(PlannerInfo        *root,
 	return srd;
 }
 
-static bool
-contain_case_expr(Node *clause)
-{
-	return contain_case_expr_walker(clause, NULL);
-}
-
-static bool
-contain_case_expr_walker(Node *node, void *context)
-{
-	if (node == NULL)
-		return false;
-
-	if (IsA(node, CaseExpr))
-		return true;
-
-	return expression_tree_walker(node, contain_case_expr_walker,
-								  context);
-}
-
 /*
  * Parallel processing of window functions.
  *
@@ -9176,47 +9151,9 @@ create_partial_window_path(PlannerInfo *root,
 {
 	PathTarget *window_target;
 	ListCell   *l;
-	Bitmapset  *sgrefs;
 
 	window_target = input_target;
 
-	sgrefs = NULL;
-
-	foreach(l, activeWindows)
-	{
-		WindowClause *wc = lfirst_node(WindowClause, l);
-		ListCell   *lc2;
-
-		foreach(lc2, wc->partitionClause)
-		{
-			SortGroupClause *sortcl = lfirst_node(SortGroupClause, lc2);
-
-			sgrefs = bms_add_member(sgrefs, sortcl->tleSortGroupRef);
-		}
-		foreach(lc2, wc->orderClause)
-		{
-			SortGroupClause *sortcl = lfirst_node(SortGroupClause, lc2);
-
-			sgrefs = bms_add_member(sgrefs, sortcl->tleSortGroupRef);
-		}
-	}
-
-	int x = -1;
-	while ((x = bms_next_member(sgrefs, x)) >= 0)
-	{
-		Index	sgref = get_pathtarget_sortgroupref(input_target, x);
-		if (sgref != 0)
-		{
-			ListCell   *lc;
-			foreach(lc, input_target->exprs)
-			{
-				Expr	*expr = (Expr *) lfirst(lc);
-				if (contain_case_expr((Node*)expr))
-					return;
-			}
-		}
-	}
-
 	foreach(l, activeWindows)
 	{
 		WindowClause *wc = lfirst_node(WindowClause, l);

src/test/regress/expected/window_parallel.out

@@ -498,7 +498,7 @@ SELECT sum(salary) OVER w, rank() OVER w FROM empsalary WINDOW w AS (PARTITION B
 (10 rows)
 
 -- w8
--- strict aggs
+-- window agg in CASE WHEN clause
 set enable_parallel = off;
 EXPLAIN(COSTS OFF)
 SELECT empno, depname, salary, bonus, depadj, MIN(bonus) OVER (ORDER BY empno), MAX(depadj) OVER () FROM(
@@ -556,12 +556,12 @@ SELECT empno, depname, salary, bonus, depadj, MIN(bonus) OVER (ORDER BY empno),
 			AVG(salary) OVER (PARTITION BY depname) < salary
 		THEN 200 END AS depadj FROM empsalary
 )s;
-                            QUERY PLAN                             
--------------------------------------------------------------------
+                                        QUERY PLAN                                        
+------------------------------------------------------------------------------------------
  WindowAgg
    ->  WindowAgg
          Order By: s.empno
-         ->  Gather Motion 3:1  (slice1; segments: 3)
+         ->  Gather Motion 6:1  (slice1; segments: 6)
                Merge Key: s.empno
                ->  Sort
                      Sort Key: s.empno
@@ -570,9 +570,12 @@ SELECT empno, depname, salary, bonus, depadj, MIN(bonus) OVER (ORDER BY empno),
                                  Partition By: empsalary.depname
                                  ->  Sort
                                        Sort Key: empsalary.depname
-                                       ->  Seq Scan on empsalary
+                                       ->  Redistribute Motion 6:6  (slice2; segments: 6)
+                                             Hash Key: empsalary.depname
+                                             Hash Module: 3
+                                             ->  Parallel Seq Scan on empsalary
  Optimizer: Postgres query optimizer
-(14 rows)
+(17 rows)
 
 SELECT empno, depname, salary, bonus, depadj, MIN(bonus) OVER (ORDER BY empno), MAX(depadj) OVER () FROM(
 	SELECT *,

src/test/regress/sql/misc_jiras.sql

@@ -21,6 +21,7 @@ set statement_mem to '1024kB';
 
 set extra_float_digits=0; -- the last decimal digits are somewhat random
 
+set enable_parallel = off;
 -- Inject fault at 'winagg_after_spool_tuples' to show that the tuplestore spills
 -- to disk.
 SELECT gp_inject_fault('winagg_after_spool_tuples', 'skip', dbid)
@@ -42,6 +43,7 @@ SELECT gp_inject_fault('winagg_after_spool_tuples', 'reset', dbid)
   FROM gp_segment_configuration WHERE role='p' AND content>=0;
 
 reset statement_mem;
+reset enable_parallel;
 
 -- non-ASCII multibyte character should show up correctly in error messages.
 select '溋' || (B'1');

src/test/regress/sql/window_parallel.sql

@@ -120,7 +120,7 @@ SELECT sum(salary) OVER w, rank() OVER w FROM empsalary WINDOW w AS (PARTITION B
 SELECT sum(salary) OVER w, rank() OVER w FROM empsalary WINDOW w AS (PARTITION BY depname ORDER BY salary DESC);
 
 -- w8
--- strict aggs
+-- window agg in CASE WHEN clause
 set enable_parallel = off;
 EXPLAIN(COSTS OFF)
 SELECT empno, depname, salary, bonus, depadj, MIN(bonus) OVER (ORDER BY empno), MAX(depadj) OVER () FROM(