Fix force_parallel_mode to work as intended.

The force_parallel_mode GUC is meant to facilitate testing of parallel
query plans, but it currently allows non-parallel plans to win even when
force_parallel_mode is enabled.
This behavior makes it difficult to debug parallel plans as intended.

Correct the behavior for testing purposes.

Authored-by: Zhang Mingli [email protected]

Author: avamingli

src/backend/optimizer/plan/planner.c

@@ -593,6 +593,8 @@ standard_planner(Query *parse, const char *query_string, int cursorOptions,
 	{
 		Path	   *cheapest_partial_path;
 		cheapest_partial_path = linitial(final_rel->partial_pathlist);
+		if (force_parallel_mode == FORCE_PARALLEL_ON)
+			final_rel->pathlist = NIL;
 		add_path(final_rel, cheapest_partial_path, root);
 		set_cheapest(final_rel);
 	}

src/test/regress/expected/incremental_sort.out

@@ -589,7 +589,6 @@ select explain_analyze_without_memory('select * from (select * from t order by a
  Optimizer: Postgres query optimizer
 (13 rows)
 
-reset max_parallel_workers_per_gather;
 select jsonb_pretty(explain_analyze_inc_sort_nodes_without_memory('select * from (select * from t order by a) s order by a, b limit 55'));
                   jsonb_pretty                   
 -------------------------------------------------
@@ -626,6 +625,7 @@ select jsonb_pretty(explain_analyze_inc_sort_nodes_without_memory('select * from
  ]
 (1 row)
 
+reset max_parallel_workers_per_gather;
 select explain_analyze_inc_sort_nodes_verify_invariants('select * from (select * from t order by a) s order by a, b limit 55');
  explain_analyze_inc_sort_nodes_verify_invariants 
 --------------------------------------------------
@@ -815,7 +815,6 @@ select explain_analyze_without_memory('select * from (select * from t order by a
  Optimizer: Postgres query optimizer
 (14 rows)
 
-reset max_parallel_workers_per_gather;
 select jsonb_pretty(explain_analyze_inc_sort_nodes_without_memory('select * from (select * from t order by a) s order by a, b limit 70'));
                   jsonb_pretty                   
 -------------------------------------------------
@@ -861,6 +860,7 @@ select jsonb_pretty(explain_analyze_inc_sort_nodes_without_memory('select * from
  ]
 (1 row)
 
+reset max_parallel_workers_per_gather;
 select explain_analyze_inc_sort_nodes_verify_invariants('select * from (select * from t order by a) s order by a, b limit 70');
  explain_analyze_inc_sort_nodes_verify_invariants 
 --------------------------------------------------

src/test/regress/expected/incremental_sort_optimizer.out

@@ -560,14 +560,14 @@ select explain_analyze_without_memory('select * from (select * from t order by a
  Optimizer: Pivotal Optimizer (GPORCA)
 (9 rows)
 
-reset max_parallel_workers_per_gather;
 select jsonb_pretty(explain_analyze_inc_sort_nodes_without_memory('select * from (select * from t order by a) s order by a, b limit 55'));
  jsonb_pretty 
 --------------
  [           +
  ]
 (1 row)
 
+reset max_parallel_workers_per_gather;
 select explain_analyze_inc_sort_nodes_verify_invariants('select * from (select * from t order by a) s order by a, b limit 55');
  explain_analyze_inc_sort_nodes_verify_invariants 
 --------------------------------------------------
@@ -743,14 +743,14 @@ select explain_analyze_without_memory('select * from (select * from t order by a
  Optimizer: Pivotal Optimizer (GPORCA)
 (10 rows)
 
-reset max_parallel_workers_per_gather;
 select jsonb_pretty(explain_analyze_inc_sort_nodes_without_memory('select * from (select * from t order by a) s order by a, b limit 70'));
  jsonb_pretty 
 --------------
  [           +
  ]
 (1 row)
 
+reset max_parallel_workers_per_gather;
 select explain_analyze_inc_sort_nodes_verify_invariants('select * from (select * from t order by a) s order by a, b limit 70');
  explain_analyze_inc_sort_nodes_verify_invariants 
 --------------------------------------------------

src/test/regress/sql/incremental_sort.sql

@@ -147,8 +147,8 @@ select * from (select * from t order by a) s order by a, b limit 55;
 -- Test EXPLAIN ANALYZE with only a fullsort group.
 set max_parallel_workers_per_gather = 0;
 select explain_analyze_without_memory('select * from (select * from t order by a) s order by a, b limit 55');
-reset max_parallel_workers_per_gather;
 select jsonb_pretty(explain_analyze_inc_sort_nodes_without_memory('select * from (select * from t order by a) s order by a, b limit 55'));
+reset max_parallel_workers_per_gather;
 select explain_analyze_inc_sort_nodes_verify_invariants('select * from (select * from t order by a) s order by a, b limit 55');
 delete from t;
 
@@ -181,8 +181,8 @@ rollback;
 -- Test EXPLAIN ANALYZE with both fullsort and presorted groups.
 set max_parallel_workers_per_gather = 0;
 select explain_analyze_without_memory('select * from (select * from t order by a) s order by a, b limit 70');
-reset max_parallel_workers_per_gather;
 select jsonb_pretty(explain_analyze_inc_sort_nodes_without_memory('select * from (select * from t order by a) s order by a, b limit 70'));
+reset max_parallel_workers_per_gather;
 select explain_analyze_inc_sort_nodes_verify_invariants('select * from (select * from t order by a) s order by a, b limit 70');
 delete from t;