Rename force_parallel_mode to debug_parallel_query

force_parallel_mode is meant to be used to allow us to exercise the
parallel query infrastructure to ensure that it's working as we expect.
It seems some users think this GUC is for forcing the query planner into
picking a parallel plan regardless of the costs.  A quick look at the
documentation would have made them realize that they were wrong, but the
GUC is likely too conveniently named which, evidently, seems to often
result in users expecting that it forces the planner into usefully
parallelizing queries.

Here we rename the GUC to something which casual users are less likely to
mistakenly think is what they need to make their query run more quickly.

For now, the old name can still be used.  We'll revisit if the old name
mapping can be removed once the buildfarm configs are all updated.

Reviewed-by: John Naylor
Discussion: https://postgr.es/m/CAApHDvrsOi92_uA7PEaHZMH-S4Xv+MGhQWA+GrP8b1kjpS1HjQ@mail.gmail.com

1 files changed, 17 insertions, 15 deletions

diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index b46e3b8c558..43b9d926600 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -360,16 +360,16 @@ static const struct config_enum_entry recovery_prefetch_options[] = {
 	{NULL, 0, false}
 };
 
-static const struct config_enum_entry force_parallel_mode_options[] = {
-	{"off", FORCE_PARALLEL_OFF, false},
-	{"on", FORCE_PARALLEL_ON, false},
-	{"regress", FORCE_PARALLEL_REGRESS, false},
-	{"true", FORCE_PARALLEL_ON, true},
-	{"false", FORCE_PARALLEL_OFF, true},
-	{"yes", FORCE_PARALLEL_ON, true},
-	{"no", FORCE_PARALLEL_OFF, true},
-	{"1", FORCE_PARALLEL_ON, true},
-	{"0", FORCE_PARALLEL_OFF, true},
+static const struct config_enum_entry debug_parallel_query_options[] = {
+	{"off", DEBUG_PARALLEL_OFF, false},
+	{"on", DEBUG_PARALLEL_ON, false},
+	{"regress", DEBUG_PARALLEL_REGRESS, false},
+	{"true", DEBUG_PARALLEL_ON, true},
+	{"false", DEBUG_PARALLEL_OFF, true},
+	{"yes", DEBUG_PARALLEL_ON, true},
+	{"no", DEBUG_PARALLEL_OFF, true},
+	{"1", DEBUG_PARALLEL_ON, true},
+	{"0", DEBUG_PARALLEL_OFF, true},
 	{NULL, 0, false}
 };
 
@@ -4852,13 +4852,15 @@ struct config_enum ConfigureNamesEnum[] =
 	},
 
 	{
-		{"force_parallel_mode", PGC_USERSET, DEVELOPER_OPTIONS,
-			gettext_noop("Forces use of parallel query facilities."),
-			gettext_noop("If possible, run query using a parallel worker and with parallel restrictions."),
+		{"debug_parallel_query", PGC_USERSET, DEVELOPER_OPTIONS,
+			gettext_noop("Forces the planner's use parallel query nodes."),
+			gettext_noop("This can be useful for testing the parallel query infrastructure "
+						 "by forcing the planner to generate plans which contains nodes "
+						 "which perform tuple communication between workers and the main process."),
 			GUC_NOT_IN_SAMPLE | GUC_EXPLAIN
 		},
-		&force_parallel_mode,
-		FORCE_PARALLEL_OFF, force_parallel_mode_options,
+		&debug_parallel_query,
+		DEBUG_PARALLEL_OFF, debug_parallel_query_options,
 		NULL, NULL, NULL
 	},