Further improve stability fix for partition_aggregate test.

Commit 7cb0a42 overlooked that the multi-level partition test table
pagg_tab_ml still had an exactly even row split at its upper level of
partitioning, so that some of the sub-aggregation plan steps still had
exactly equal costs, leading to plan instability.  Tweak the partition
boundaries some more to make the row distribution unequal at both
levels.  This leads to more changes in the "expected" plan order than
the previous round, but it seems fine.  (Actually, I'm surprised that
this didn't affect even more plans in this test: looking at the
underlying costs shows that some of the parallel plan groups are
*not* getting sorted by cost.  Bug?)

Per buildfarm member lousyjack,
https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=lousyjack&dt=2020-04-04%2021%3A03%3A04

Discussion: https://postgr.es/m/24467.1585838693@sss.pgh.pa.us

Author: tglsfdc

src/test/regress/expected/partition_aggregate.out

@@ -926,8 +926,8 @@ SELECT a, c, sum(b), avg(c), count(*) FROM pagg_tab_m GROUP BY (a+b)/2, 2, 1 HAV
 
 -- Test with multi-level partitioning scheme
 CREATE TABLE pagg_tab_ml (a int, b int, c text) PARTITION BY RANGE(a);
-CREATE TABLE pagg_tab_ml_p1 PARTITION OF pagg_tab_ml FOR VALUES FROM (0) TO (10);
-CREATE TABLE pagg_tab_ml_p2 PARTITION OF pagg_tab_ml FOR VALUES FROM (10) TO (20) PARTITION BY LIST (c);
+CREATE TABLE pagg_tab_ml_p1 PARTITION OF pagg_tab_ml FOR VALUES FROM (0) TO (12);
+CREATE TABLE pagg_tab_ml_p2 PARTITION OF pagg_tab_ml FOR VALUES FROM (12) TO (20) PARTITION BY LIST (c);
 CREATE TABLE pagg_tab_ml_p2_s1 PARTITION OF pagg_tab_ml_p2 FOR VALUES IN ('0000', '0001', '0002');
 CREATE TABLE pagg_tab_ml_p2_s2 PARTITION OF pagg_tab_ml_p2 FOR VALUES IN ('0003');
 -- This level of partitioning has different column positions than the parent
@@ -946,21 +946,19 @@ SET max_parallel_workers_per_gather TO 2;
 -- is not partial agg safe.
 EXPLAIN (COSTS OFF)
 SELECT a, sum(b), array_agg(distinct c), count(*) FROM pagg_tab_ml GROUP BY a HAVING avg(b) < 3 ORDER BY 1, 2, 3;
-                                         QUERY PLAN                                         
---------------------------------------------------------------------------------------------
+                                      QUERY PLAN                                      
+--------------------------------------------------------------------------------------
  Sort
-   Sort Key: pagg_tab_ml_2.a, (sum(pagg_tab_ml_2.b)), (array_agg(DISTINCT pagg_tab_ml_2.c))
+   Sort Key: pagg_tab_ml.a, (sum(pagg_tab_ml.b)), (array_agg(DISTINCT pagg_tab_ml.c))
    ->  Gather
          Workers Planned: 2
          ->  Parallel Append
                ->  GroupAggregate
-                     Group Key: pagg_tab_ml_2.a
-                     Filter: (avg(pagg_tab_ml_2.b) < '3'::numeric)
+                     Group Key: pagg_tab_ml.a
+                     Filter: (avg(pagg_tab_ml.b) < '3'::numeric)
                      ->  Sort
-                           Sort Key: pagg_tab_ml_2.a
-                           ->  Append
-                                 ->  Seq Scan on pagg_tab_ml_p2_s1 pagg_tab_ml_2
-                                 ->  Seq Scan on pagg_tab_ml_p2_s2 pagg_tab_ml_3
+                           Sort Key: pagg_tab_ml.a
+                           ->  Seq Scan on pagg_tab_ml_p1 pagg_tab_ml
                ->  GroupAggregate
                      Group Key: pagg_tab_ml_5.a
                      Filter: (avg(pagg_tab_ml_5.b) < '3'::numeric)
@@ -970,11 +968,13 @@ SELECT a, sum(b), array_agg(distinct c), count(*) FROM pagg_tab_ml GROUP BY a HA
                                  ->  Seq Scan on pagg_tab_ml_p3_s1 pagg_tab_ml_5
                                  ->  Seq Scan on pagg_tab_ml_p3_s2 pagg_tab_ml_6
                ->  GroupAggregate
-                     Group Key: pagg_tab_ml.a
-                     Filter: (avg(pagg_tab_ml.b) < '3'::numeric)
+                     Group Key: pagg_tab_ml_2.a
+                     Filter: (avg(pagg_tab_ml_2.b) < '3'::numeric)
                      ->  Sort
-                           Sort Key: pagg_tab_ml.a
-                           ->  Seq Scan on pagg_tab_ml_p1 pagg_tab_ml
+                           Sort Key: pagg_tab_ml_2.a
+                           ->  Append
+                                 ->  Seq Scan on pagg_tab_ml_p2_s1 pagg_tab_ml_2
+                                 ->  Seq Scan on pagg_tab_ml_p2_s2 pagg_tab_ml_3
 (27 rows)
 
 SELECT a, sum(b), array_agg(distinct c), count(*) FROM pagg_tab_ml GROUP BY a HAVING avg(b) < 3 ORDER BY 1, 2, 3;
@@ -1000,13 +1000,11 @@ SELECT a, sum(b), array_agg(distinct c), count(*) FROM pagg_tab_ml GROUP BY a HA
    Workers Planned: 2
    ->  Parallel Append
          ->  GroupAggregate
-               Group Key: pagg_tab_ml_2.a
-               Filter: (avg(pagg_tab_ml_2.b) < '3'::numeric)
+               Group Key: pagg_tab_ml.a
+               Filter: (avg(pagg_tab_ml.b) < '3'::numeric)
                ->  Sort
-                     Sort Key: pagg_tab_ml_2.a
-                     ->  Append
-                           ->  Seq Scan on pagg_tab_ml_p2_s1 pagg_tab_ml_2
-                           ->  Seq Scan on pagg_tab_ml_p2_s2 pagg_tab_ml_3
+                     Sort Key: pagg_tab_ml.a
+                     ->  Seq Scan on pagg_tab_ml_p1 pagg_tab_ml
          ->  GroupAggregate
                Group Key: pagg_tab_ml_5.a
                Filter: (avg(pagg_tab_ml_5.b) < '3'::numeric)
@@ -1016,11 +1014,13 @@ SELECT a, sum(b), array_agg(distinct c), count(*) FROM pagg_tab_ml GROUP BY a HA
                            ->  Seq Scan on pagg_tab_ml_p3_s1 pagg_tab_ml_5
                            ->  Seq Scan on pagg_tab_ml_p3_s2 pagg_tab_ml_6
          ->  GroupAggregate
-               Group Key: pagg_tab_ml.a
-               Filter: (avg(pagg_tab_ml.b) < '3'::numeric)
+               Group Key: pagg_tab_ml_2.a
+               Filter: (avg(pagg_tab_ml_2.b) < '3'::numeric)
                ->  Sort
-                     Sort Key: pagg_tab_ml.a
-                     ->  Seq Scan on pagg_tab_ml_p1 pagg_tab_ml
+                     Sort Key: pagg_tab_ml_2.a
+                     ->  Append
+                           ->  Seq Scan on pagg_tab_ml_p2_s1 pagg_tab_ml_2
+                           ->  Seq Scan on pagg_tab_ml_p2_s2 pagg_tab_ml_3
 (25 rows)
 
 -- Full aggregation at level 1 as GROUP BY clause matches with PARTITION KEY
@@ -1249,12 +1249,12 @@ SELECT b, sum(a), count(*) FROM pagg_tab_ml GROUP BY b ORDER BY 1, 2, 3;
                            ->  Partial HashAggregate
                                  Group Key: pagg_tab_ml.b
                                  ->  Parallel Seq Scan on pagg_tab_ml_p1 pagg_tab_ml
-                           ->  Partial HashAggregate
-                                 Group Key: pagg_tab_ml_1.b
-                                 ->  Parallel Seq Scan on pagg_tab_ml_p2_s1 pagg_tab_ml_1
                            ->  Partial HashAggregate
                                  Group Key: pagg_tab_ml_3.b
                                  ->  Parallel Seq Scan on pagg_tab_ml_p3_s1 pagg_tab_ml_3
+                           ->  Partial HashAggregate
+                                 Group Key: pagg_tab_ml_1.b
+                                 ->  Parallel Seq Scan on pagg_tab_ml_p2_s1 pagg_tab_ml_1
                            ->  Partial HashAggregate
                                  Group Key: pagg_tab_ml_4.b
                                  ->  Parallel Seq Scan on pagg_tab_ml_p3_s2 pagg_tab_ml_4
@@ -1287,14 +1287,14 @@ SELECT a, sum(b), count(*) FROM pagg_tab_ml GROUP BY a, b, c HAVING avg(b) > 7 O
                      Group Key: pagg_tab_ml.a, pagg_tab_ml.b, pagg_tab_ml.c
                      Filter: (avg(pagg_tab_ml.b) > '7'::numeric)
                      ->  Seq Scan on pagg_tab_ml_p1 pagg_tab_ml
-               ->  HashAggregate
-                     Group Key: pagg_tab_ml_1.a, pagg_tab_ml_1.b, pagg_tab_ml_1.c
-                     Filter: (avg(pagg_tab_ml_1.b) > '7'::numeric)
-                     ->  Seq Scan on pagg_tab_ml_p2_s1 pagg_tab_ml_1
                ->  HashAggregate
                      Group Key: pagg_tab_ml_3.a, pagg_tab_ml_3.b, pagg_tab_ml_3.c
                      Filter: (avg(pagg_tab_ml_3.b) > '7'::numeric)
                      ->  Seq Scan on pagg_tab_ml_p3_s1 pagg_tab_ml_3
+               ->  HashAggregate
+                     Group Key: pagg_tab_ml_1.a, pagg_tab_ml_1.b, pagg_tab_ml_1.c
+                     Filter: (avg(pagg_tab_ml_1.b) > '7'::numeric)
+                     ->  Seq Scan on pagg_tab_ml_p2_s1 pagg_tab_ml_1
                ->  HashAggregate
                      Group Key: pagg_tab_ml_4.a, pagg_tab_ml_4.b, pagg_tab_ml_4.c
                      Filter: (avg(pagg_tab_ml_4.b) > '7'::numeric)

src/test/regress/sql/partition_aggregate.sql

@@ -202,8 +202,8 @@ SELECT a, c, sum(b), avg(c), count(*) FROM pagg_tab_m GROUP BY (a+b)/2, 2, 1 HAV
 -- Test with multi-level partitioning scheme
 
 CREATE TABLE pagg_tab_ml (a int, b int, c text) PARTITION BY RANGE(a);
-CREATE TABLE pagg_tab_ml_p1 PARTITION OF pagg_tab_ml FOR VALUES FROM (0) TO (10);
-CREATE TABLE pagg_tab_ml_p2 PARTITION OF pagg_tab_ml FOR VALUES FROM (10) TO (20) PARTITION BY LIST (c);
+CREATE TABLE pagg_tab_ml_p1 PARTITION OF pagg_tab_ml FOR VALUES FROM (0) TO (12);
+CREATE TABLE pagg_tab_ml_p2 PARTITION OF pagg_tab_ml FOR VALUES FROM (12) TO (20) PARTITION BY LIST (c);
 CREATE TABLE pagg_tab_ml_p2_s1 PARTITION OF pagg_tab_ml_p2 FOR VALUES IN ('0000', '0001', '0002');
 CREATE TABLE pagg_tab_ml_p2_s2 PARTITION OF pagg_tab_ml_p2 FOR VALUES IN ('0003');