0001-Add-new-GUC-parameter-enable_groupagg-WIP-r1.patch

From 461c64770e612661d974acc0fd39815108781580 Mon Sep 17 00:00:00 2001
From: Tatsuro Yamada <yamatattsu@gmail.com>
Date: Thu, 5 Jun 2025 18:50:34 +0900
Subject: [PATCH] Add new GUC parameter: enable_groupagg

Previously, there was no GUC parameter to control the use of
GroupAggregate, so we couldn't influence the planner's choice
 in certain queries.
This patch adds a new parameter, "enable_groupagg", which
allows users to enable or disable GroupAggregate explicitly.

By disabling GroupAggregate, the planner may choose
HashAggregate instead, potentially resulting in a more
efficient execution plan for some queries.
---
 doc/src/sgml/config.sgml                      | 14 ++++++++++++++
 src/backend/optimizer/path/costsize.c         |  3 +++
 src/backend/utils/misc/guc_tables.c           | 10 ++++++++++
 src/backend/utils/misc/postgresql.conf.sample |  1 +
 src/include/optimizer/cost.h                  |  1 +
 src/test/regress/expected/sysviews.out        |  3 ++-
 6 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 021153b2a5f..edd0f3a13b8 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -5515,6 +5515,20 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-enable-groupagg" xreflabel="enable_groupagg">
+      <term><varname>enable_groupagg</varname> (<type>boolean</type>)
+      <indexterm>
+       <primary><varname>enable_groupagg</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Enables or disables the query planner's use of grouped
+        aggregation plan types. The default is <literal>on</literal>.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-enable-hashjoin" xreflabel="enable_hashjoin">
       <term><varname>enable_hashjoin</varname> (<type>boolean</type>)
       <indexterm>
diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index 3d44815ed5a..80c68008d85 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -150,6 +150,7 @@ bool		enable_tidscan = true;
 bool		enable_sort = true;
 bool		enable_incremental_sort = true;
 bool		enable_hashagg = true;
+bool		enable_groupagg = true;
 bool		enable_nestloop = true;
 bool		enable_material = true;
 bool		enable_memoize = true;
@@ -2737,6 +2738,8 @@ cost_agg(Path *path, PlannerInfo *root,
 		/* Here we are able to deliver output on-the-fly */
 		startup_cost = input_startup_cost;
 		total_cost = input_total_cost;
+		if (aggstrategy == AGG_SORTED && !enable_groupagg && enable_hashagg)
+			++disabled_nodes;
 		if (aggstrategy == AGG_MIXED && !enable_hashagg)
 			++disabled_nodes;
 		/* calcs phrased this way to match HASHED case, see note above */
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index f04bfedb2fd..a17b7fb1ba1 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -869,6 +869,16 @@ struct config_bool ConfigureNamesBool[] =
 		true,
 		NULL, NULL, NULL
 	},
+	{
+		{"enable_groupagg", PGC_USERSET, QUERY_TUNING_METHOD,
+			gettext_noop("Enables the planner's use of grouped aggregation plans."),
+			NULL,
+			GUC_EXPLAIN
+		},
+		&enable_groupagg,
+		true,
+		NULL, NULL, NULL
+	},
 	{
 		{"enable_material", PGC_USERSET, QUERY_TUNING_METHOD,
 			gettext_noop("Enables the planner's use of materialization."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 341f88adc87..0514c327767 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -408,6 +408,7 @@
 #enable_bitmapscan = on
 #enable_gathermerge = on
 #enable_hashagg = on
+#enable_groupagg = on
 #enable_hashjoin = on
 #enable_incremental_sort = on
 #enable_indexscan = on
diff --git a/src/include/optimizer/cost.h b/src/include/optimizer/cost.h
index d397fe27dc1..099d41fd7bd 100644
--- a/src/include/optimizer/cost.h
+++ b/src/include/optimizer/cost.h
@@ -57,6 +57,7 @@ extern PGDLLIMPORT bool enable_tidscan;
 extern PGDLLIMPORT bool enable_sort;
 extern PGDLLIMPORT bool enable_incremental_sort;
 extern PGDLLIMPORT bool enable_hashagg;
+extern PGDLLIMPORT bool enable_groupagg;
 extern PGDLLIMPORT bool enable_nestloop;
 extern PGDLLIMPORT bool enable_material;
 extern PGDLLIMPORT bool enable_memoize;
diff --git a/src/test/regress/expected/sysviews.out b/src/test/regress/expected/sysviews.out
index 83228cfca29..f10371d6e26 100644
--- a/src/test/regress/expected/sysviews.out
+++ b/src/test/regress/expected/sysviews.out
@@ -153,6 +153,7 @@ select name, setting from pg_settings where name like 'enable%';
  enable_distinct_reordering     | on
  enable_gathermerge             | on
  enable_group_by_reordering     | on
+ enable_groupagg                | on
  enable_hashagg                 | on
  enable_hashjoin                | on
  enable_incremental_sort        | on
@@ -172,7 +173,7 @@ select name, setting from pg_settings where name like 'enable%';
  enable_seqscan                 | on
  enable_sort                    | on
  enable_tidscan                 | on
-(24 rows)
+(25 rows)
 
 -- There are always wait event descriptions for various types.  InjectionPoint
 -- may be present or absent, depending on history since last postmaster start.
-- 
2.43.5