Subject: [PATCH 4/4] add force_incremental_sort GUC

From: Tomas Vondra <[email-masked]>
Date: Tue, 9 Jul 2019 13:36:42 +0200

---
 src/backend/optimizer/path/costsize.c |  8 ++++++++
 src/backend/utils/misc/guc.c          | 10 ++++++++++
 src/include/optimizer/cost.h          |  1 +
 3 files changed, 19 insertions(+)

diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index c6aa17ba67..ee4487b158 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -140,6 +140,8 @@ bool		enable_parallel_append = true;
 bool		enable_parallel_hash = true;
 bool		enable_partition_pruning = true;
 
+bool		force_incremental_sort = true;
+
 typedef struct
 {
 	PlannerInfo *root;
@@ -1907,6 +1909,12 @@ cost_incremental_sort(Path *path,
 	path->rows = input_tuples;
 	path->startup_cost = startup_cost;
 	path->total_cost = startup_cost + run_cost;
+
+	if (force_incremental_sort)
+	{
+		path->startup_cost = input_startup_cost;
+		path->total_cost = input_total_cost;
+	}
 }
 
 /*
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index f922ee66a0..d2cc5b56b5 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -941,6 +941,16 @@ static struct config_bool ConfigureNamesBool[] =
 		true,
 		NULL, NULL, NULL
 	},
+	{
+		{"force_incremental_sort", PGC_USERSET, QUERY_TUNING_METHOD,
+			gettext_noop("Makes the incremental sort look like no-cost."),
+			NULL,
+			GUC_EXPLAIN
+		},
+		&force_incremental_sort,
+		false,
+		NULL, NULL, NULL
+	},
 	{
 		{"enable_incrementalsort", PGC_USERSET, QUERY_TUNING_METHOD,
 			gettext_noop("Enables the planner's use of incremental sort steps."),
diff --git a/src/include/optimizer/cost.h b/src/include/optimizer/cost.h
index b9d7a77e65..bad1d5a330 100644
--- a/src/include/optimizer/cost.h
+++ b/src/include/optimizer/cost.h
@@ -66,6 +66,7 @@ extern PGDLLIMPORT bool enable_parallel_append;
 extern PGDLLIMPORT bool enable_parallel_hash;
 extern PGDLLIMPORT bool enable_partition_pruning;
 extern PGDLLIMPORT int constraint_exclusion;
+extern PGDLLIMPORT bool force_incremental_sort;
 
 extern double index_pages_fetched(double tuples_fetched, BlockNumber pages,
 								  double index_pages, PlannerInfo *root);
-- 
2.21.0

--z44ikx7gwyo2xwzv--