Fix force_parallel_mode to work as intended.

avamingli · avamingli · commit b7389be37492 · 2025-08-02T08:11:59.000+08:00
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 avamingli@gmail.com
diff --git a/src/backend/optimizer/plan/planner.c b/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);
 	}

Original file line number	Diff line number	Diff line change
`@@ -593,6 +593,8 @@ standard_planner(Query parse, const char query_string, int cursorOptions,`
`593`	`593`	`{`
`594`	`594`	`Path *cheapest_partial_path;`
`595`	`595`	`cheapest_partial_path = linitial(final_rel->partial_pathlist);`
	`596`	`+ if (force_parallel_mode == FORCE_PARALLEL_ON)`
	`597`	`+ final_rel->pathlist = NIL;`
`596`	`598`	`add_path(final_rel, cheapest_partial_path, root);`
`597`	`599`	`set_cheapest(final_rel);`
`598`	`600`	`}`