v3-0001-Add-parallel-counters-to-pg_stat_statements.patch

From 0d88ddd09f0f6f9df71f3d43af31205df58d63b5 Mon Sep 17 00:00:00 2001
From: Daymel Bonne <daymelbonne@gmail.com>
Date: Sat, 13 Aug 2022 20:23:04 +0000
Subject: [PATCH v3] Add parallel counters to pg_stat_statements

---
 contrib/pg_stat_statements/Makefile           |  2 +-
 .../expected/oldextversions.out               | 58 ++++++++++++++++
 .../expected/pg_stat_statements.out           | 48 +++++++++++++
 .../pg_stat_statements--1.10--1.11.sql        | 69 +++++++++++++++++++
 .../pg_stat_statements/pg_stat_statements.c   | 62 ++++++++++++++---
 .../pg_stat_statements.control                |  2 +-
 .../pg_stat_statements/sql/oldextversions.sql |  5 ++
 .../sql/pg_stat_statements.sql                | 25 +++++++
 doc/src/sgml/pgstatstatements.sgml            | 34 +++++++++
 src/backend/executor/execUtils.c              |  1 +
 src/backend/executor/nodeGather.c             |  7 ++
 src/backend/executor/nodeGatherMerge.c        |  7 ++
 src/include/nodes/execnodes.h                 |  1 +
 13 files changed, 311 insertions(+), 10 deletions(-)
 create mode 100644 contrib/pg_stat_statements/pg_stat_statements--1.10--1.11.sql

diff --git a/contrib/pg_stat_statements/Makefile b/contrib/pg_stat_statements/Makefile
index edc40c8bbf..0afb9060fa 100644
--- a/contrib/pg_stat_statements/Makefile
+++ b/contrib/pg_stat_statements/Makefile
@@ -6,7 +6,7 @@ OBJS = \
 	pg_stat_statements.o
 
 EXTENSION = pg_stat_statements
-DATA = pg_stat_statements--1.4.sql \
+DATA = pg_stat_statements--1.4.sql pg_stat_statements--1.10--1.11.sql \
 	pg_stat_statements--1.9--1.10.sql pg_stat_statements--1.8--1.9.sql \
 	pg_stat_statements--1.7--1.8.sql pg_stat_statements--1.6--1.7.sql \
 	pg_stat_statements--1.5--1.6.sql pg_stat_statements--1.4--1.5.sql \
diff --git a/contrib/pg_stat_statements/expected/oldextversions.out b/contrib/pg_stat_statements/expected/oldextversions.out
index efb2049ecf..410e7963e0 100644
--- a/contrib/pg_stat_statements/expected/oldextversions.out
+++ b/contrib/pg_stat_statements/expected/oldextversions.out
@@ -250,4 +250,62 @@ SELECT count(*) > 0 AS has_data FROM pg_stat_statements;
  t
 (1 row)
 
+-- Added parallel counters for pg_stat_statements in 1.11
+AlTER EXTENSION pg_stat_statements UPDATE TO '1.11';
+\d pg_stat_statements
+                      View "public.pg_stat_statements"
+         Column         |       Type       | Collation | Nullable | Default 
+------------------------+------------------+-----------+----------+---------
+ userid                 | oid              |           |          | 
+ dbid                   | oid              |           |          | 
+ toplevel               | boolean          |           |          | 
+ queryid                | bigint           |           |          | 
+ query                  | text             |           |          | 
+ plans                  | bigint           |           |          | 
+ total_plan_time        | double precision |           |          | 
+ min_plan_time          | double precision |           |          | 
+ max_plan_time          | double precision |           |          | 
+ mean_plan_time         | double precision |           |          | 
+ stddev_plan_time       | double precision |           |          | 
+ calls                  | bigint           |           |          | 
+ total_exec_time        | double precision |           |          | 
+ min_exec_time          | double precision |           |          | 
+ max_exec_time          | double precision |           |          | 
+ mean_exec_time         | double precision |           |          | 
+ stddev_exec_time       | double precision |           |          | 
+ rows                   | bigint           |           |          | 
+ shared_blks_hit        | bigint           |           |          | 
+ shared_blks_read       | bigint           |           |          | 
+ shared_blks_dirtied    | bigint           |           |          | 
+ shared_blks_written    | bigint           |           |          | 
+ local_blks_hit         | bigint           |           |          | 
+ local_blks_read        | bigint           |           |          | 
+ local_blks_dirtied     | bigint           |           |          | 
+ local_blks_written     | bigint           |           |          | 
+ temp_blks_read         | bigint           |           |          | 
+ temp_blks_written      | bigint           |           |          | 
+ blk_read_time          | double precision |           |          | 
+ blk_write_time         | double precision |           |          | 
+ temp_blk_read_time     | double precision |           |          | 
+ temp_blk_write_time    | double precision |           |          | 
+ wal_records            | bigint           |           |          | 
+ wal_fpi                | bigint           |           |          | 
+ wal_bytes              | numeric          |           |          | 
+ jit_functions          | bigint           |           |          | 
+ jit_generation_time    | double precision |           |          | 
+ jit_inlining_count     | bigint           |           |          | 
+ jit_inlining_time      | double precision |           |          | 
+ jit_optimization_count | bigint           |           |          | 
+ jit_optimization_time  | double precision |           |          | 
+ jit_emission_count     | bigint           |           |          | 
+ jit_emission_time      | double precision |           |          | 
+ paral_planned_exec     | bigint           |           |          | 
+ paral_planned_not_exec | bigint           |           |          | 
+
+SELECT count(*) > 0 AS has_data FROM pg_stat_statements;
+ has_data 
+----------
+ t
+(1 row)
+
 DROP EXTENSION pg_stat_statements;
diff --git a/contrib/pg_stat_statements/expected/pg_stat_statements.out b/contrib/pg_stat_statements/expected/pg_stat_statements.out
index ff0166fb9d..0e09d8bc57 100644
--- a/contrib/pg_stat_statements/expected/pg_stat_statements.out
+++ b/contrib/pg_stat_statements/expected/pg_stat_statements.out
@@ -1102,4 +1102,52 @@ SELECT COUNT(*) FROM pg_stat_statements WHERE query LIKE '%SELECT GROUPING%';
      2
 (1 row)
 
+-- encourage use of parallel plans
+SET parallel_setup_cost=0;
+SET parallel_tuple_cost=0;
+SET min_parallel_table_scan_size=0;
+SET max_parallel_workers_per_gather=4;
+SELECT pg_stat_statements_reset();
+ pg_stat_statements_reset 
+--------------------------
+ 
+(1 row)
+
+CREATE TABLE pgss_test as select generate_series(1, 1000) i;
+SELECT COUNT(1) from pgss_test WHERE i % 2 = 0;
+ count 
+-------
+   500
+(1 row)
+
+SELECT paral_planned_exec = 1, paral_planned_not_exec = 0 from pg_stat_statements WHERE query LIKE '%COUNT%';
+ ?column? | ?column? 
+----------+----------
+ t        | t
+(1 row)
+
+SELECT pg_stat_statements_reset();
+ pg_stat_statements_reset 
+--------------------------
+ 
+(1 row)
+
+SET max_parallel_workers = 0;
+SELECT COUNT(1) from pgss_test WHERE i % 2 = 0;
+ count 
+-------
+   500
+(1 row)
+
+SELECT paral_planned_exec = 0, paral_planned_not_exec = 1 from pg_stat_statements WHERE query LIKE '%COUNT%';
+ ?column? | ?column? 
+----------+----------
+ t        | t
+(1 row)
+
+DROP TABLE pgss_test;
+RESET parallel_setup_cost;
+RESET parallel_tuple_cost;
+RESET min_parallel_table_scan_size;
+RESET max_parallel_workers_per_gather;
 DROP EXTENSION pg_stat_statements;
diff --git a/contrib/pg_stat_statements/pg_stat_statements--1.10--1.11.sql b/contrib/pg_stat_statements/pg_stat_statements--1.10--1.11.sql
new file mode 100644
index 0000000000..902f86657f
--- /dev/null
+++ b/contrib/pg_stat_statements/pg_stat_statements--1.10--1.11.sql
@@ -0,0 +1,69 @@
+/* contrib/pg_stat_statements/pg_stat_statements--1.10--1.11.sql */
+
+-- complain if script is sourced in psql, rather than via ALTER EXTENSION
+\echo Use "ALTER EXTENSION pg_stat_statements UPDATE TO '1.11'" to load this file. \quit
+
+/* First we have to remove them from the extension */
+ALTER EXTENSION pg_stat_statements DROP VIEW pg_stat_statements;
+ALTER EXTENSION pg_stat_statements DROP FUNCTION pg_stat_statements(boolean);
+
+/* Then we can drop them */
+DROP VIEW pg_stat_statements;
+DROP FUNCTION pg_stat_statements(boolean);
+
+/* Now redefine */
+CREATE FUNCTION pg_stat_statements(IN showtext boolean,
+    OUT userid oid,
+    OUT dbid oid,
+    OUT toplevel bool,
+    OUT queryid bigint,
+    OUT query text,
+    OUT plans int8,
+    OUT total_plan_time float8,
+    OUT min_plan_time float8,
+    OUT max_plan_time float8,
+    OUT mean_plan_time float8,
+    OUT stddev_plan_time float8,
+    OUT calls int8,
+    OUT total_exec_time float8,
+    OUT min_exec_time float8,
+    OUT max_exec_time float8,
+    OUT mean_exec_time float8,
+    OUT stddev_exec_time float8,
+    OUT rows int8,
+    OUT shared_blks_hit int8,
+    OUT shared_blks_read int8,
+    OUT shared_blks_dirtied int8,
+    OUT shared_blks_written int8,
+    OUT local_blks_hit int8,
+    OUT local_blks_read int8,
+    OUT local_blks_dirtied int8,
+    OUT local_blks_written int8,
+    OUT temp_blks_read int8,
+    OUT temp_blks_written int8,
+    OUT blk_read_time float8,
+    OUT blk_write_time float8,
+    OUT temp_blk_read_time float8,
+    OUT temp_blk_write_time float8,
+    OUT wal_records int8,
+    OUT wal_fpi int8,
+    OUT wal_bytes numeric,
+    OUT jit_functions int8,
+    OUT jit_generation_time float8,
+    OUT jit_inlining_count int8,
+    OUT jit_inlining_time float8,
+    OUT jit_optimization_count int8,
+    OUT jit_optimization_time float8,
+    OUT jit_emission_count int8,
+    OUT jit_emission_time float8,
+    OUT paral_planned_exec int8,
+    OUT paral_planned_not_exec int8
+)
+RETURNS SETOF record
+AS 'MODULE_PATHNAME', 'pg_stat_statements_1_11'
+LANGUAGE C STRICT VOLATILE PARALLEL SAFE;
+
+CREATE VIEW pg_stat_statements AS
+  SELECT * FROM pg_stat_statements(true);
+
+GRANT SELECT ON pg_stat_statements TO PUBLIC;
diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c
index ba868f0de9..43fead4fdd 100644
--- a/contrib/pg_stat_statements/pg_stat_statements.c
+++ b/contrib/pg_stat_statements/pg_stat_statements.c
@@ -118,7 +118,8 @@ typedef enum pgssVersion
 	PGSS_V1_3,
 	PGSS_V1_8,
 	PGSS_V1_9,
-	PGSS_V1_10
+	PGSS_V1_10,
+	PGSS_V1_11
 } pgssVersion;
 
 typedef enum pgssStoreKind
@@ -200,6 +201,9 @@ typedef struct Counters
 	int64		jit_emission_count; /* number of times emission time has been
 									 * > 0 */
 	double		jit_emission_time;	/* total time to emit jit code */
+	int64       paral_planned_exec;		/* # of times was executed using parallelism */
+	int64       paral_planned_not_exec;	/* # of times was planned to use parallelism
+										 * but was not executed using parallelism */
 } Counters;
 
 /*
@@ -312,6 +316,7 @@ PG_FUNCTION_INFO_V1(pg_stat_statements_1_3);
 PG_FUNCTION_INFO_V1(pg_stat_statements_1_8);
 PG_FUNCTION_INFO_V1(pg_stat_statements_1_9);
 PG_FUNCTION_INFO_V1(pg_stat_statements_1_10);
+PG_FUNCTION_INFO_V1(pg_stat_statements_1_11);
 PG_FUNCTION_INFO_V1(pg_stat_statements);
 PG_FUNCTION_INFO_V1(pg_stat_statements_info);
 
@@ -342,7 +347,9 @@ static void pgss_store(const char *query, uint64 queryId,
 					   const BufferUsage *bufusage,
 					   const WalUsage *walusage,
 					   const struct JitInstrumentation *jitusage,
-					   JumbleState *jstate);
+					   JumbleState *jstate,
+					   bool paral_executed,
+					   bool paral_planned);
 static void pg_stat_statements_internal(FunctionCallInfo fcinfo,
 										pgssVersion api_version,
 										bool showtext);
@@ -857,7 +864,9 @@ pgss_post_parse_analyze(ParseState *pstate, Query *query, JumbleState *jstate)
 				   NULL,
 				   NULL,
 				   NULL,
-				   jstate);
+				   jstate,
+				   false,
+				   false);
 }
 
 /*
@@ -942,7 +951,9 @@ pgss_planner(Query *parse,
 				   &bufusage,
 				   &walusage,
 				   NULL,
-				   NULL);
+				   NULL,
+				   false,
+				   false);
 	}
 	else
 	{
@@ -1061,7 +1072,9 @@ pgss_ExecutorEnd(QueryDesc *queryDesc)
 				   &queryDesc->totaltime->bufusage,
 				   &queryDesc->totaltime->walusage,
 				   queryDesc->estate->es_jit ? &queryDesc->estate->es_jit->instr : NULL,
-				   NULL);
+				   NULL,
+				   queryDesc->estate->es_parallel_mode_exec,
+				   queryDesc->plannedstmt->parallelModeNeeded);
 	}
 
 	if (prev_ExecutorEnd)
@@ -1179,7 +1192,9 @@ pgss_ProcessUtility(PlannedStmt *pstmt, const char *queryString,
 				   &bufusage,
 				   &walusage,
 				   NULL,
-				   NULL);
+				   NULL,
+				   false,
+				   false);
 	}
 	else
 	{
@@ -1213,7 +1228,9 @@ pgss_store(const char *query, uint64 queryId,
 		   const BufferUsage *bufusage,
 		   const WalUsage *walusage,
 		   const struct JitInstrumentation *jitusage,
-		   JumbleState *jstate)
+		   JumbleState *jstate,
+		   bool paral_executed,
+		   bool paral_planned)
 {
 	pgssHashKey key;
 	pgssEntry  *entry;
@@ -1399,6 +1416,15 @@ pgss_store(const char *query, uint64 queryId,
 				e->counters.jit_emission_count++;
 			e->counters.jit_emission_time += INSTR_TIME_GET_MILLISEC(jitusage->emission_counter);
 		}
+		/* inc parallel counters */
+		if (paral_executed)
+		{
+			e->counters.paral_planned_exec += 1;
+		}
+		if (paral_planned && !paral_executed)
+		{
+			e->counters.paral_planned_not_exec += 1;
+		}
 
 		SpinLockRelease(&e->mutex);
 	}
@@ -1449,7 +1475,8 @@ pg_stat_statements_reset(PG_FUNCTION_ARGS)
 #define PG_STAT_STATEMENTS_COLS_V1_8	32
 #define PG_STAT_STATEMENTS_COLS_V1_9	33
 #define PG_STAT_STATEMENTS_COLS_V1_10	43
-#define PG_STAT_STATEMENTS_COLS			43	/* maximum of above */
+#define PG_STAT_STATEMENTS_COLS_V1_11	45
+#define PG_STAT_STATEMENTS_COLS			45	/* maximum of above */
 
 /*
  * Retrieve statement statistics.
@@ -1461,6 +1488,15 @@ pg_stat_statements_reset(PG_FUNCTION_ARGS)
  * expected API version is identified by embedding it in the C name of the
  * function.  Unfortunately we weren't bright enough to do that for 1.1.
  */
+Datum
+pg_stat_statements_1_11(PG_FUNCTION_ARGS)
+{
+	bool		showtext = PG_GETARG_BOOL(0);
+	pg_stat_statements_internal(fcinfo, PGSS_V1_11, showtext);
+
+	return (Datum) 0;
+}
+
 Datum
 pg_stat_statements_1_10(PG_FUNCTION_ARGS)
 {
@@ -1591,6 +1627,10 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo,
 			if (api_version != PGSS_V1_10)
 				elog(ERROR, "incorrect number of output arguments");
 			break;
+		case PG_STAT_STATEMENTS_COLS_V1_11:
+			if (api_version != PGSS_V1_11)
+				elog(ERROR, "incorrect number of output arguments");
+			break;
 		default:
 			elog(ERROR, "incorrect number of output arguments");
 	}
@@ -1823,6 +1863,11 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo,
 			values[i++] = Int64GetDatumFast(tmp.jit_emission_count);
 			values[i++] = Float8GetDatumFast(tmp.jit_emission_time);
 		}
+		if (api_version >= PGSS_V1_11)
+		{
+			values[i++] = Int64GetDatumFast(tmp.paral_planned_exec);
+			values[i++] = Int64GetDatumFast(tmp.paral_planned_not_exec);
+		}
 
 		Assert(i == (api_version == PGSS_V1_0 ? PG_STAT_STATEMENTS_COLS_V1_0 :
 					 api_version == PGSS_V1_1 ? PG_STAT_STATEMENTS_COLS_V1_1 :
@@ -1831,6 +1876,7 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo,
 					 api_version == PGSS_V1_8 ? PG_STAT_STATEMENTS_COLS_V1_8 :
 					 api_version == PGSS_V1_9 ? PG_STAT_STATEMENTS_COLS_V1_9 :
 					 api_version == PGSS_V1_10 ? PG_STAT_STATEMENTS_COLS_V1_10 :
+					 api_version == PGSS_V1_11 ? PG_STAT_STATEMENTS_COLS_V1_11 :
 					 -1 /* fail if you forget to update this assert */ ));
 
 		tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
diff --git a/contrib/pg_stat_statements/pg_stat_statements.control b/contrib/pg_stat_statements/pg_stat_statements.control
index 0747e48138..8a76106ec6 100644
--- a/contrib/pg_stat_statements/pg_stat_statements.control
+++ b/contrib/pg_stat_statements/pg_stat_statements.control
@@ -1,5 +1,5 @@
 # pg_stat_statements extension
 comment = 'track planning and execution statistics of all SQL statements executed'
-default_version = '1.10'
+default_version = '1.11'
 module_pathname = '$libdir/pg_stat_statements'
 relocatable = true
diff --git a/contrib/pg_stat_statements/sql/oldextversions.sql b/contrib/pg_stat_statements/sql/oldextversions.sql
index e2a83106d4..381f5c396d 100644
--- a/contrib/pg_stat_statements/sql/oldextversions.sql
+++ b/contrib/pg_stat_statements/sql/oldextversions.sql
@@ -48,4 +48,9 @@ AlTER EXTENSION pg_stat_statements UPDATE TO '1.10';
 \d pg_stat_statements
 SELECT count(*) > 0 AS has_data FROM pg_stat_statements;
 
+-- Added parallel counters for pg_stat_statements in 1.11
+AlTER EXTENSION pg_stat_statements UPDATE TO '1.11';
+\d pg_stat_statements
+SELECT count(*) > 0 AS has_data FROM pg_stat_statements;
+
 DROP EXTENSION pg_stat_statements;
diff --git a/contrib/pg_stat_statements/sql/pg_stat_statements.sql b/contrib/pg_stat_statements/sql/pg_stat_statements.sql
index a01f183727..856f8034ff 100644
--- a/contrib/pg_stat_statements/sql/pg_stat_statements.sql
+++ b/contrib/pg_stat_statements/sql/pg_stat_statements.sql
@@ -442,4 +442,29 @@ SELECT (
 
 SELECT COUNT(*) FROM pg_stat_statements WHERE query LIKE '%SELECT GROUPING%';
 
+-- encourage use of parallel plans
+SET parallel_setup_cost=0;
+SET parallel_tuple_cost=0;
+SET min_parallel_table_scan_size=0;
+SET max_parallel_workers_per_gather=4;
+
+SELECT pg_stat_statements_reset();
+CREATE TABLE pgss_test as select generate_series(1, 1000) i;
+
+SELECT COUNT(1) from pgss_test WHERE i % 2 = 0;
+SELECT paral_planned_exec = 1, paral_planned_not_exec = 0 from pg_stat_statements WHERE query LIKE '%COUNT%';
+
+SELECT pg_stat_statements_reset();
+SET max_parallel_workers = 0;
+
+SELECT COUNT(1) from pgss_test WHERE i % 2 = 0;
+SELECT paral_planned_exec = 0, paral_planned_not_exec = 1 from pg_stat_statements WHERE query LIKE '%COUNT%';
+
+DROP TABLE pgss_test;
+
+RESET parallel_setup_cost;
+RESET parallel_tuple_cost;
+RESET min_parallel_table_scan_size;
+RESET max_parallel_workers_per_gather;
+
 DROP EXTENSION pg_stat_statements;
diff --git a/doc/src/sgml/pgstatstatements.sgml b/doc/src/sgml/pgstatstatements.sgml
index ecf6cd6bf3..a658c813b7 100644
--- a/doc/src/sgml/pgstatstatements.sgml
+++ b/doc/src/sgml/pgstatstatements.sgml
@@ -473,6 +473,26 @@
        Total time spent by the statement on emitting code, in milliseconds
       </para></entry>
      </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>paral_planned_exec</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of times that the statement was executed using parallelism.
+       See <xref linkend="pgstatstatements-paral-counter-limitations"/>
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>paral_planned_not_exec</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of times the statement was planned to use parallelism but
+       was not executed using parallelism. See <xref linkend="pgstatstatements-paral-counter-limitations"/>
+      </para></entry>
+     </row>
     </tbody>
    </tgroup>
   </table>
@@ -961,6 +981,20 @@ hit_percent     |
 </screen>
  </sect2>
 
+ <sect2>
+  <title>Limitations</title>
+  <para>
+   <itemizedlist>
+    <listitem id="pgstatstatements-paral-counter-limitations" xreflabel="Parallel counters limitations">
+     <para>
+      <literal>paral_planned_exec</literal> and <literal>paral_planned_not_exec</literal> do not
+      include statistics from utility statements such as CREATE INDEX or VACUUM.
+     </para>
+    </listitem>
+   </itemizedlist>
+  </para>
+ </sect2>
+
  <sect2>
   <title>Authors</title>
 
diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
index 9df1f81ea8..b3d178e53f 100644
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -155,6 +155,7 @@ CreateExecutorState(void)
 	estate->es_sourceText = NULL;
 
 	estate->es_use_parallel_mode = false;
+	estate->es_parallel_mode_exec = false;
 
 	estate->es_jit_flags = 0;
 	estate->es_jit = NULL;
diff --git a/src/backend/executor/nodeGather.c b/src/backend/executor/nodeGather.c
index 1283d5b737..5524783848 100644
--- a/src/backend/executor/nodeGather.c
+++ b/src/backend/executor/nodeGather.c
@@ -187,6 +187,13 @@ ExecGather(PlanState *pstate)
 			/* We save # workers launched for the benefit of EXPLAIN */
 			node->nworkers_launched = pcxt->nworkers_launched;
 
+			/*
+			 * We save that the plan used parallelism if at least one
+			 * of the nodes was able to launch a worker.
+			 */
+			if(pcxt->nworkers_launched > 0)
+				estate->es_parallel_mode_exec = true;
+
 			/* Set up tuple queue readers to read the results. */
 			if (pcxt->nworkers_launched > 0)
 			{
diff --git a/src/backend/executor/nodeGatherMerge.c b/src/backend/executor/nodeGatherMerge.c
index 3b1007f352..d71eb597c4 100644
--- a/src/backend/executor/nodeGatherMerge.c
+++ b/src/backend/executor/nodeGatherMerge.c
@@ -228,6 +228,13 @@ ExecGatherMerge(PlanState *pstate)
 			/* We save # workers launched for the benefit of EXPLAIN */
 			node->nworkers_launched = pcxt->nworkers_launched;
 
+			/*
+			 * We save that the plan used parallelism if at least one
+			 * of the nodes was able to launch a worker.
+			 */
+			if(pcxt->nworkers_launched > 0)
+				estate->es_parallel_mode_exec = true;
+
 			/* Set up tuple queue readers to read the results. */
 			if (pcxt->nworkers_launched > 0)
 			{
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 01b1727fc0..0d4f081051 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -676,6 +676,7 @@ typedef struct EState
 	struct EPQState *es_epq_active;
 
 	bool		es_use_parallel_mode;	/* can we use parallel workers? */
+	bool		es_parallel_mode_exec;	/* was executed in parallel */
 
 	/* The per-query shared memory area to use for parallel execution. */
 	struct dsa_area *es_query_dsa;

base-commit: adee0df127e088a47c58801fc5a412392297e1da
-- 
2.30.2