Parallel workers stats in pg_stat_database

From 0338cfb11ab98594b2f16d143b505e269566bb6e Mon Sep 17 00:00:00 2001
From: benoit <benoit.lobreau@dalibo.com>
Date: Wed, 28 Aug 2024 02:27:13 +0200
Subject: [PATCH] Adds four parallel workers stat columns to pg_stat_database

* parallel_workers_planned
* parallel_workers_launched
* parallel_maint_workers_planned
* parallel_maint_workers_launched
---
 doc/src/sgml/monitoring.sgml                 | 36 ++++++++++++++++++++
 src/backend/access/brin/brin.c               |  4 +++
 src/backend/access/nbtree/nbtsort.c          |  4 +++
 src/backend/catalog/system_views.sql         |  4 +++
 src/backend/commands/vacuumparallel.c        |  5 +++
 src/backend/executor/execMain.c              |  5 +++
 src/backend/executor/execUtils.c             |  3 ++
 src/backend/executor/nodeGather.c            |  3 ++
 src/backend/executor/nodeGatherMerge.c       |  3 ++
 src/backend/utils/activity/pgstat_database.c | 36 ++++++++++++++++++++
 src/backend/utils/adt/pgstatfuncs.c          | 12 +++++++
 src/include/catalog/pg_proc.dat              | 20 +++++++++++
 src/include/nodes/execnodes.h                |  3 ++
 src/include/pgstat.h                         |  7 ++++
 src/test/regress/expected/rules.out          |  4 +++
 src/test/regress/expected/stats.out          | 17 +++++++++
 src/test/regress/sql/stats.sql               | 14 ++++++++
 17 files changed, 180 insertions(+)

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 55417a6fa9..8c4b11c11d 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3508,6 +3508,42 @@ description | Waiting for a newly initialized WAL file to reach durable storage
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_workers_planned</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers planned by queries on this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_workers_launched</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers obtained by queries on this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_maint_workers_planned</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers planned by utilities on this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_maint_workers_launched</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers obtained by utilities on this database
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c
index 6467bed604..9eceb87b52 100644
--- a/src/backend/access/brin/brin.c
+++ b/src/backend/access/brin/brin.c
@@ -2540,6 +2540,10 @@ _brin_end_parallel(BrinLeader *brinleader, BrinBuildState *state)
 	/* Shutdown worker processes */
 	WaitForParallelWorkersToFinish(brinleader->pcxt);
 
+	pgstat_update_parallel_maint_workers_stats(
+		(PgStat_Counter) brinleader->pcxt->nworkers_to_launch,
+		(PgStat_Counter) brinleader->pcxt->nworkers_launched);
+
 	/*
 	 * Next, accumulate WAL usage.  (This must wait for the workers to finish,
 	 * or we might get incomplete data.)
diff --git a/src/backend/access/nbtree/nbtsort.c b/src/backend/access/nbtree/nbtsort.c
index f5d7b3b0c3..232e1a0942 100644
--- a/src/backend/access/nbtree/nbtsort.c
+++ b/src/backend/access/nbtree/nbtsort.c
@@ -1611,6 +1611,10 @@ _bt_end_parallel(BTLeader *btleader)
 	/* Shutdown worker processes */
 	WaitForParallelWorkersToFinish(btleader->pcxt);
 
+	pgstat_update_parallel_maint_workers_stats(
+		(PgStat_Counter) btleader->pcxt->nworkers_to_launch,
+		(PgStat_Counter) btleader->pcxt->nworkers_launched);
+
 	/*
 	 * Next, accumulate WAL usage.  (This must wait for the workers to finish,
 	 * or we might get incomplete data.)
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 19cabc9a47..48bf9e5535 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1073,6 +1073,10 @@ CREATE VIEW pg_stat_database AS
             pg_stat_get_db_sessions_abandoned(D.oid) AS sessions_abandoned,
             pg_stat_get_db_sessions_fatal(D.oid) AS sessions_fatal,
             pg_stat_get_db_sessions_killed(D.oid) AS sessions_killed,
+            pg_stat_get_db_parallel_workers_planned(D.oid) as parallel_workers_planned,
+            pg_stat_get_db_parallel_workers_launched(D.oid) as parallel_workers_launched,
+            pg_stat_get_db_parallel_maint_workers_planned(D.oid) as parallel_maint_workers_planned,
+            pg_stat_get_db_parallel_maint_workers_launched(D.oid) as parallel_maint_workers_launched,
             pg_stat_get_db_stat_reset_time(D.oid) AS stats_reset
     FROM (
         SELECT 0 AS oid, NULL::name AS datname
diff --git a/src/backend/commands/vacuumparallel.c b/src/backend/commands/vacuumparallel.c
index 22c057fe61..f7603a0863 100644
--- a/src/backend/commands/vacuumparallel.c
+++ b/src/backend/commands/vacuumparallel.c
@@ -435,6 +435,11 @@ parallel_vacuum_end(ParallelVacuumState *pvs, IndexBulkDeleteResult **istats)
 {
 	Assert(!IsParallelWorker());
 
+	pgstat_update_parallel_maint_workers_stats(
+		(PgStat_Counter) pvs->pcxt->nworkers_to_launch,
+		(PgStat_Counter) pvs->pcxt->nworkers_launched
+	);
+
 	/* Copy the updated statistics */
 	for (int i = 0; i < pvs->nindexes; i++)
 	{
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index 29e186fa73..baeb88629a 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -51,6 +51,7 @@
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
 #include "parser/parse_relation.h"
+#include "pgstat.h"
 #include "rewrite/rewriteHandler.h"
 #include "tcop/utility.h"
 #include "utils/acl.h"
@@ -480,6 +481,10 @@ standard_ExecutorEnd(QueryDesc *queryDesc)
 
 	Assert(estate != NULL);
 
+	pgstat_update_parallel_workers_stats(
+		(PgStat_Counter) estate->es_workers_planned,
+		(PgStat_Counter) estate->es_workers_launched);
+
 	/*
 	 * Check that ExecutorFinish was called, unless in EXPLAIN-only mode. This
 	 * Assert is needed because ExecutorFinish is new as of 9.1, and callers
diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
index 5737f9f4eb..5919902075 100644
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -162,6 +162,9 @@ CreateExecutorState(void)
 	estate->es_jit_flags = 0;
 	estate->es_jit = NULL;
 
+	estate->es_workers_launched = 0;
+	estate->es_workers_planned = 0;
+
 	/*
 	 * Return the executor state structure
 	 */
diff --git a/src/backend/executor/nodeGather.c b/src/backend/executor/nodeGather.c
index 5d4ffe989c..1271a0f7d1 100644
--- a/src/backend/executor/nodeGather.c
+++ b/src/backend/executor/nodeGather.c
@@ -182,6 +182,9 @@ ExecGather(PlanState *pstate)
 			/* We save # workers launched for the benefit of EXPLAIN */
 			node->nworkers_launched = pcxt->nworkers_launched;
 
+			estate->es_workers_launched += pcxt->nworkers_launched;
+			estate->es_workers_planned += pcxt->nworkers_to_launch;
+
 			/* 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 45f6017c29..677c450c3d 100644
--- a/src/backend/executor/nodeGatherMerge.c
+++ b/src/backend/executor/nodeGatherMerge.c
@@ -223,6 +223,9 @@ ExecGatherMerge(PlanState *pstate)
 			/* We save # workers launched for the benefit of EXPLAIN */
 			node->nworkers_launched = pcxt->nworkers_launched;
 
+			estate->es_workers_launched += pcxt->nworkers_launched;
+			estate->es_workers_planned += pcxt->nworkers_to_launch;
+
 			/* Set up tuple queue readers to read the results. */
 			if (pcxt->nworkers_launched > 0)
 			{
diff --git a/src/backend/utils/activity/pgstat_database.c b/src/backend/utils/activity/pgstat_database.c
index 29bc090974..9e72c286b2 100644
--- a/src/backend/utils/activity/pgstat_database.c
+++ b/src/backend/utils/activity/pgstat_database.c
@@ -262,6 +262,38 @@ AtEOXact_PgStat_Database(bool isCommit, bool parallel)
 	}
 }
 
+/*
+ * reports parallel_workers_planned and parallel_workers_launched into
+ * PgStat_StatDBEntry
+ */
+void
+pgstat_update_parallel_workers_stats(PgStat_Counter parallel_workers_planned, PgStat_Counter parallel_workers_launched)
+{
+	PgStat_StatDBEntry *dbentry;
+	if (!OidIsValid(MyDatabaseId))
+		return;
+
+	dbentry = pgstat_prep_database_pending(MyDatabaseId);
+	dbentry->parallel_workers_planned += parallel_workers_planned;
+	dbentry->parallel_workers_launched += parallel_workers_launched;
+}
+
+/*
+ * reports parallel_maint_workers_planned and parallel_maint_workers_launched into
+ * PgStat_StatDBEntry
+ */
+void
+pgstat_update_parallel_maint_workers_stats(PgStat_Counter parallel_maint_workers_planned, PgStat_Counter parallel_maint_workers_launched)
+{
+	PgStat_StatDBEntry *dbentry;
+	if (!OidIsValid(MyDatabaseId))
+		return;
+
+	dbentry = pgstat_prep_database_pending(MyDatabaseId);
+	dbentry->parallel_maint_workers_planned += parallel_maint_workers_planned;
+	dbentry->parallel_maint_workers_launched += parallel_maint_workers_launched;
+}
+
 /*
  * Subroutine for pgstat_report_stat(): Handle xact commit/rollback and I/O
  * timings.
@@ -425,6 +457,10 @@ pgstat_database_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
 	PGSTAT_ACCUM_DBCOUNT(sessions_abandoned);
 	PGSTAT_ACCUM_DBCOUNT(sessions_fatal);
 	PGSTAT_ACCUM_DBCOUNT(sessions_killed);
+	PGSTAT_ACCUM_DBCOUNT(parallel_workers_planned);
+	PGSTAT_ACCUM_DBCOUNT(parallel_workers_launched);
+	PGSTAT_ACCUM_DBCOUNT(parallel_maint_workers_planned);
+	PGSTAT_ACCUM_DBCOUNT(parallel_maint_workers_launched);
 #undef PGSTAT_ACCUM_DBCOUNT
 
 	pgstat_unlock_entry(entry_ref);
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 3221137123..377a0f6453 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1039,6 +1039,18 @@ PG_STAT_GET_DBENTRY_INT64(sessions_fatal)
 /* pg_stat_get_db_sessions_killed */
 PG_STAT_GET_DBENTRY_INT64(sessions_killed)
 
+/* pg_stat_get_db_parallel_workers_planned*/
+PG_STAT_GET_DBENTRY_INT64(parallel_workers_planned)
+
+/* pg_stat_get_db_parallel_workers_launched*/
+PG_STAT_GET_DBENTRY_INT64(parallel_workers_launched)
+
+/* pg_stat_get_db_parallel_maint_workers_planned*/
+PG_STAT_GET_DBENTRY_INT64(parallel_maint_workers_planned)
+
+/* pg_stat_get_db_parallel_maint_workers_launched*/
+PG_STAT_GET_DBENTRY_INT64(parallel_maint_workers_launched)
+
 /* pg_stat_get_db_temp_bytes */
 PG_STAT_GET_DBENTRY_INT64(temp_bytes)
 
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 4abc6d9526..b1cd4fa1b0 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5751,6 +5751,26 @@
   proname => 'pg_stat_get_db_sessions_killed', provolatile => 's',
   proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
   prosrc => 'pg_stat_get_db_sessions_killed' },
+{ oid => '8403',
+  descr => 'statistics: number of parallel workers planned for queries',
+  proname => 'pg_stat_get_db_parallel_workers_planned', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_workers_planned' },
+{ oid => '8404',
+  descr => 'statistics: number of parallel workers effectively launched for queries',
+  proname => 'pg_stat_get_db_parallel_workers_launched', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_workers_launched' },
+{ oid => '8405',
+  descr => 'statistics: number of parallel workers planned for utilities',
+  proname => 'pg_stat_get_db_parallel_maint_workers_planned', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_maint_workers_planned' },
+{ oid => '8406',
+  descr => 'statistics: number of parallel workers effectively launched for utilities',
+  proname => 'pg_stat_get_db_parallel_maint_workers_launched', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_maint_workers_launched' },
 { oid => '3195', descr => 'statistics: information about WAL archiver',
   proname => 'pg_stat_get_archiver', proisstrict => 'f', provolatile => 's',
   proparallel => 'r', prorettype => 'record', proargtypes => '',
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index af7d8fd1e7..1903ad60f8 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -724,6 +724,9 @@ typedef struct EState
 	 */
 	List	   *es_insert_pending_result_relations;
 	List	   *es_insert_pending_modifytables;
+
+	int			es_workers_launched;
+	int			es_workers_planned;
 } EState;
 
 
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index f63159c55c..bad74a9f2d 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -383,6 +383,11 @@ typedef struct PgStat_StatDBEntry
 	PgStat_Counter sessions_fatal;
 	PgStat_Counter sessions_killed;
 
+	PgStat_Counter parallel_workers_planned;
+	PgStat_Counter parallel_workers_launched;
+	PgStat_Counter parallel_maint_workers_planned;
+	PgStat_Counter parallel_maint_workers_launched;
+
 	TimestampTz stat_reset_timestamp;
 } PgStat_StatDBEntry;
 
@@ -578,6 +583,8 @@ extern void pgstat_report_deadlock(void);
 extern void pgstat_report_checksum_failures_in_db(Oid dboid, int failurecount);
 extern void pgstat_report_checksum_failure(void);
 extern void pgstat_report_connect(Oid dboid);
+extern void pgstat_update_parallel_workers_stats(PgStat_Counter parallel_workers_planned, PgStat_Counter parallel_workers_launched);
+extern void pgstat_update_parallel_maint_workers_stats(PgStat_Counter parallel_maint_workers_planned, PgStat_Counter parallel_maint_workers_launched);
 
 #define pgstat_count_buffer_read_time(n)							\
 	(pgStatBlockReadTime += (n))
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 862433ee52..e8a4453cd5 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1861,6 +1861,10 @@ pg_stat_database| SELECT oid AS datid,
     pg_stat_get_db_sessions_abandoned(oid) AS sessions_abandoned,
     pg_stat_get_db_sessions_fatal(oid) AS sessions_fatal,
     pg_stat_get_db_sessions_killed(oid) AS sessions_killed,
+    pg_stat_get_db_parallel_workers_planned(oid) AS parallel_workers_planned,
+    pg_stat_get_db_parallel_workers_launched(oid) AS parallel_workers_launched,
+    pg_stat_get_db_parallel_maint_workers_planned(oid) AS parallel_maint_workers_planned,
+    pg_stat_get_db_parallel_maint_workers_launched(oid) AS parallel_maint_workers_launched,
     pg_stat_get_db_stat_reset_time(oid) AS stats_reset
    FROM ( SELECT 0 AS oid,
             NULL::name AS datname
diff --git a/src/test/regress/expected/stats.out b/src/test/regress/expected/stats.out
index 6e08898b18..88d283a991 100644
--- a/src/test/regress/expected/stats.out
+++ b/src/test/regress/expected/stats.out
@@ -32,6 +32,11 @@ SELECT t.seq_scan, t.seq_tup_read, t.idx_scan, t.idx_tup_fetch,
        pg_catalog.pg_statio_user_tables AS b
  WHERE t.relname='tenk2' AND b.relname='tenk2';
 COMMIT;
+SELECT sum(parallel_workers_planned) AS parallel_workers_planned_before,
+       sum(parallel_workers_launched) AS parallel_workers_launched_before,
+       sum(parallel_maint_workers_planned) AS parallel_maint_workers_planned_before,
+       sum(parallel_maint_workers_launched) AS parallel_maint_workers_launched_before
+FROM pg_stat_database \gset
 -- test effects of TRUNCATE on n_live_tup/n_dead_tup counters
 CREATE TABLE trunc_stats_test(id serial);
 CREATE TABLE trunc_stats_test1(id serial, stuff text);
@@ -862,6 +867,18 @@ WHERE pg_stat_get_backend_pid(beid) = pg_backend_pid();
  t
 (1 row)
 
+-- Test that parallel workers stats are updated in pg_stat_database
+SELECT
+  sum(parallel_workers_planned) > :'parallel_workers_planned_before' AS wrk_planned,
+  sum(parallel_workers_launched) > :'parallel_workers_launched_before' AS wrk_launched,
+  sum(parallel_maint_workers_planned) > :'parallel_maint_workers_planned_before' AS maint_wrk_planned,
+  sum(parallel_maint_workers_launched) > :'parallel_maint_workers_launched_before' AS maint_wrk_launched
+FROM pg_stat_database;
+ wrk_planned | wrk_launched | maint_wrk_planned | maint_wrk_launched 
+-------------+--------------+-------------------+--------------------
+ t           | t            | t                 | t
+(1 row)
+
 -----
 -- Test that resetting stats works for reset timestamp
 -----
diff --git a/src/test/regress/sql/stats.sql b/src/test/regress/sql/stats.sql
index d8ac0d06f4..3a59c75539 100644
--- a/src/test/regress/sql/stats.sql
+++ b/src/test/regress/sql/stats.sql
@@ -32,6 +32,12 @@ SELECT t.seq_scan, t.seq_tup_read, t.idx_scan, t.idx_tup_fetch,
  WHERE t.relname='tenk2' AND b.relname='tenk2';
 COMMIT;
 
+SELECT sum(parallel_workers_planned) AS parallel_workers_planned_before,
+       sum(parallel_workers_launched) AS parallel_workers_launched_before,
+       sum(parallel_maint_workers_planned) AS parallel_maint_workers_planned_before,
+       sum(parallel_maint_workers_launched) AS parallel_maint_workers_launched_before
+FROM pg_stat_database \gset
+
 -- test effects of TRUNCATE on n_live_tup/n_dead_tup counters
 CREATE TABLE trunc_stats_test(id serial);
 CREATE TABLE trunc_stats_test1(id serial, stuff text);
@@ -442,6 +448,14 @@ SELECT (current_schemas(true))[1] = ('pg_temp_' || beid::text) AS match
 FROM pg_stat_get_backend_idset() beid
 WHERE pg_stat_get_backend_pid(beid) = pg_backend_pid();
 
+-- Test that parallel workers stats are updated in pg_stat_database
+SELECT
+  sum(parallel_workers_planned) > :'parallel_workers_planned_before' AS wrk_planned,
+  sum(parallel_workers_launched) > :'parallel_workers_launched_before' AS wrk_launched,
+  sum(parallel_maint_workers_planned) > :'parallel_maint_workers_planned_before' AS maint_wrk_planned,
+  sum(parallel_maint_workers_launched) > :'parallel_maint_workers_launched_before' AS maint_wrk_launched
+FROM pg_stat_database;
+
 -----
 -- Test that resetting stats works for reset timestamp
 -----
-- 
2.45.2

From 5e4401c865f77ed447b8b3f25aac0ffa9af0d700 Mon Sep 17 00:00:00 2001
From: benoit <benoit.lobreau@dalibo.com>
Date: Wed, 28 Aug 2024 02:27:13 +0200
Subject: [PATCH] Adds four parallel workers stat columns to pg_stat_database

* parallel_workers_planned
* parallel_workers_launched
* parallel_maint_workers_planned
* parallel_maint_workers_launched
---
 doc/src/sgml/monitoring.sgml                 | 36 ++++++++++++++++++++
 src/backend/access/brin/brin.c               |  4 +++
 src/backend/access/nbtree/nbtsort.c          |  4 +++
 src/backend/catalog/system_views.sql         |  4 +++
 src/backend/commands/vacuumparallel.c        |  5 +++
 src/backend/executor/execMain.c              |  7 ++++
 src/backend/executor/execUtils.c             |  3 ++
 src/backend/executor/nodeGather.c            |  3 ++
 src/backend/executor/nodeGatherMerge.c       |  3 ++
 src/backend/utils/activity/pgstat_database.c | 36 ++++++++++++++++++++
 src/backend/utils/adt/pgstatfuncs.c          | 12 +++++++
 src/include/catalog/pg_proc.dat              | 20 +++++++++++
 src/include/nodes/execnodes.h                |  3 ++
 src/include/pgstat.h                         |  7 ++++
 src/test/regress/expected/rules.out          |  4 +++
 src/test/regress/expected/stats.out          | 17 +++++++++
 src/test/regress/sql/stats.sql               | 14 ++++++++
 17 files changed, 182 insertions(+)

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 55417a6fa9..8c4b11c11d 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3508,6 +3508,42 @@ description | Waiting for a newly initialized WAL file to reach durable storage
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_workers_planned</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers planned by queries on this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_workers_launched</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers obtained by queries on this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_maint_workers_planned</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers planned by utilities on this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_maint_workers_launched</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers obtained by utilities on this database
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c
index 6467bed604..9eceb87b52 100644
--- a/src/backend/access/brin/brin.c
+++ b/src/backend/access/brin/brin.c
@@ -2540,6 +2540,10 @@ _brin_end_parallel(BrinLeader *brinleader, BrinBuildState *state)
 	/* Shutdown worker processes */
 	WaitForParallelWorkersToFinish(brinleader->pcxt);
 
+	pgstat_update_parallel_maint_workers_stats(
+		(PgStat_Counter) brinleader->pcxt->nworkers_to_launch,
+		(PgStat_Counter) brinleader->pcxt->nworkers_launched);
+
 	/*
 	 * Next, accumulate WAL usage.  (This must wait for the workers to finish,
 	 * or we might get incomplete data.)
diff --git a/src/backend/access/nbtree/nbtsort.c b/src/backend/access/nbtree/nbtsort.c
index f5d7b3b0c3..232e1a0942 100644
--- a/src/backend/access/nbtree/nbtsort.c
+++ b/src/backend/access/nbtree/nbtsort.c
@@ -1611,6 +1611,10 @@ _bt_end_parallel(BTLeader *btleader)
 	/* Shutdown worker processes */
 	WaitForParallelWorkersToFinish(btleader->pcxt);
 
+	pgstat_update_parallel_maint_workers_stats(
+		(PgStat_Counter) btleader->pcxt->nworkers_to_launch,
+		(PgStat_Counter) btleader->pcxt->nworkers_launched);
+
 	/*
 	 * Next, accumulate WAL usage.  (This must wait for the workers to finish,
 	 * or we might get incomplete data.)
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 19cabc9a47..48bf9e5535 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1073,6 +1073,10 @@ CREATE VIEW pg_stat_database AS
             pg_stat_get_db_sessions_abandoned(D.oid) AS sessions_abandoned,
             pg_stat_get_db_sessions_fatal(D.oid) AS sessions_fatal,
             pg_stat_get_db_sessions_killed(D.oid) AS sessions_killed,
+            pg_stat_get_db_parallel_workers_planned(D.oid) as parallel_workers_planned,
+            pg_stat_get_db_parallel_workers_launched(D.oid) as parallel_workers_launched,
+            pg_stat_get_db_parallel_maint_workers_planned(D.oid) as parallel_maint_workers_planned,
+            pg_stat_get_db_parallel_maint_workers_launched(D.oid) as parallel_maint_workers_launched,
             pg_stat_get_db_stat_reset_time(D.oid) AS stats_reset
     FROM (
         SELECT 0 AS oid, NULL::name AS datname
diff --git a/src/backend/commands/vacuumparallel.c b/src/backend/commands/vacuumparallel.c
index 22c057fe61..f7603a0863 100644
--- a/src/backend/commands/vacuumparallel.c
+++ b/src/backend/commands/vacuumparallel.c
@@ -435,6 +435,11 @@ parallel_vacuum_end(ParallelVacuumState *pvs, IndexBulkDeleteResult **istats)
 {
 	Assert(!IsParallelWorker());
 
+	pgstat_update_parallel_maint_workers_stats(
+		(PgStat_Counter) pvs->pcxt->nworkers_to_launch,
+		(PgStat_Counter) pvs->pcxt->nworkers_launched
+	);
+
 	/* Copy the updated statistics */
 	for (int i = 0; i < pvs->nindexes; i++)
 	{
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index 29e186fa73..9bf5f57b65 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -51,6 +51,7 @@
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
 #include "parser/parse_relation.h"
+#include "pgstat.h"
 #include "rewrite/rewriteHandler.h"
 #include "tcop/utility.h"
 #include "utils/acl.h"
@@ -480,6 +481,12 @@ standard_ExecutorEnd(QueryDesc *queryDesc)
 
 	Assert(estate != NULL);
 
+	if (estate->es_workers_planned > 0) {
+		pgstat_update_parallel_workers_stats(
+			(PgStat_Counter) estate->es_workers_planned,
+			(PgStat_Counter) estate->es_workers_launched);
+	}
+
 	/*
 	 * Check that ExecutorFinish was called, unless in EXPLAIN-only mode. This
 	 * Assert is needed because ExecutorFinish is new as of 9.1, and callers
diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
index 5737f9f4eb..5919902075 100644
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -162,6 +162,9 @@ CreateExecutorState(void)
 	estate->es_jit_flags = 0;
 	estate->es_jit = NULL;
 
+	estate->es_workers_launched = 0;
+	estate->es_workers_planned = 0;
+
 	/*
 	 * Return the executor state structure
 	 */
diff --git a/src/backend/executor/nodeGather.c b/src/backend/executor/nodeGather.c
index 5d4ffe989c..1271a0f7d1 100644
--- a/src/backend/executor/nodeGather.c
+++ b/src/backend/executor/nodeGather.c
@@ -182,6 +182,9 @@ ExecGather(PlanState *pstate)
 			/* We save # workers launched for the benefit of EXPLAIN */
 			node->nworkers_launched = pcxt->nworkers_launched;
 
+			estate->es_workers_launched += pcxt->nworkers_launched;
+			estate->es_workers_planned += pcxt->nworkers_to_launch;
+
 			/* 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 45f6017c29..677c450c3d 100644
--- a/src/backend/executor/nodeGatherMerge.c
+++ b/src/backend/executor/nodeGatherMerge.c
@@ -223,6 +223,9 @@ ExecGatherMerge(PlanState *pstate)
 			/* We save # workers launched for the benefit of EXPLAIN */
 			node->nworkers_launched = pcxt->nworkers_launched;
 
+			estate->es_workers_launched += pcxt->nworkers_launched;
+			estate->es_workers_planned += pcxt->nworkers_to_launch;
+
 			/* Set up tuple queue readers to read the results. */
 			if (pcxt->nworkers_launched > 0)
 			{
diff --git a/src/backend/utils/activity/pgstat_database.c b/src/backend/utils/activity/pgstat_database.c
index 29bc090974..9e72c286b2 100644
--- a/src/backend/utils/activity/pgstat_database.c
+++ b/src/backend/utils/activity/pgstat_database.c
@@ -262,6 +262,38 @@ AtEOXact_PgStat_Database(bool isCommit, bool parallel)
 	}
 }
 
+/*
+ * reports parallel_workers_planned and parallel_workers_launched into
+ * PgStat_StatDBEntry
+ */
+void
+pgstat_update_parallel_workers_stats(PgStat_Counter parallel_workers_planned, PgStat_Counter parallel_workers_launched)
+{
+	PgStat_StatDBEntry *dbentry;
+	if (!OidIsValid(MyDatabaseId))
+		return;
+
+	dbentry = pgstat_prep_database_pending(MyDatabaseId);
+	dbentry->parallel_workers_planned += parallel_workers_planned;
+	dbentry->parallel_workers_launched += parallel_workers_launched;
+}
+
+/*
+ * reports parallel_maint_workers_planned and parallel_maint_workers_launched into
+ * PgStat_StatDBEntry
+ */
+void
+pgstat_update_parallel_maint_workers_stats(PgStat_Counter parallel_maint_workers_planned, PgStat_Counter parallel_maint_workers_launched)
+{
+	PgStat_StatDBEntry *dbentry;
+	if (!OidIsValid(MyDatabaseId))
+		return;
+
+	dbentry = pgstat_prep_database_pending(MyDatabaseId);
+	dbentry->parallel_maint_workers_planned += parallel_maint_workers_planned;
+	dbentry->parallel_maint_workers_launched += parallel_maint_workers_launched;
+}
+
 /*
  * Subroutine for pgstat_report_stat(): Handle xact commit/rollback and I/O
  * timings.
@@ -425,6 +457,10 @@ pgstat_database_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
 	PGSTAT_ACCUM_DBCOUNT(sessions_abandoned);
 	PGSTAT_ACCUM_DBCOUNT(sessions_fatal);
 	PGSTAT_ACCUM_DBCOUNT(sessions_killed);
+	PGSTAT_ACCUM_DBCOUNT(parallel_workers_planned);
+	PGSTAT_ACCUM_DBCOUNT(parallel_workers_launched);
+	PGSTAT_ACCUM_DBCOUNT(parallel_maint_workers_planned);
+	PGSTAT_ACCUM_DBCOUNT(parallel_maint_workers_launched);
 #undef PGSTAT_ACCUM_DBCOUNT
 
 	pgstat_unlock_entry(entry_ref);
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 3221137123..377a0f6453 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1039,6 +1039,18 @@ PG_STAT_GET_DBENTRY_INT64(sessions_fatal)
 /* pg_stat_get_db_sessions_killed */
 PG_STAT_GET_DBENTRY_INT64(sessions_killed)
 
+/* pg_stat_get_db_parallel_workers_planned*/
+PG_STAT_GET_DBENTRY_INT64(parallel_workers_planned)
+
+/* pg_stat_get_db_parallel_workers_launched*/
+PG_STAT_GET_DBENTRY_INT64(parallel_workers_launched)
+
+/* pg_stat_get_db_parallel_maint_workers_planned*/
+PG_STAT_GET_DBENTRY_INT64(parallel_maint_workers_planned)
+
+/* pg_stat_get_db_parallel_maint_workers_launched*/
+PG_STAT_GET_DBENTRY_INT64(parallel_maint_workers_launched)
+
 /* pg_stat_get_db_temp_bytes */
 PG_STAT_GET_DBENTRY_INT64(temp_bytes)
 
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 4abc6d9526..b1cd4fa1b0 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5751,6 +5751,26 @@
   proname => 'pg_stat_get_db_sessions_killed', provolatile => 's',
   proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
   prosrc => 'pg_stat_get_db_sessions_killed' },
+{ oid => '8403',
+  descr => 'statistics: number of parallel workers planned for queries',
+  proname => 'pg_stat_get_db_parallel_workers_planned', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_workers_planned' },
+{ oid => '8404',
+  descr => 'statistics: number of parallel workers effectively launched for queries',
+  proname => 'pg_stat_get_db_parallel_workers_launched', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_workers_launched' },
+{ oid => '8405',
+  descr => 'statistics: number of parallel workers planned for utilities',
+  proname => 'pg_stat_get_db_parallel_maint_workers_planned', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_maint_workers_planned' },
+{ oid => '8406',
+  descr => 'statistics: number of parallel workers effectively launched for utilities',
+  proname => 'pg_stat_get_db_parallel_maint_workers_launched', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_maint_workers_launched' },
 { oid => '3195', descr => 'statistics: information about WAL archiver',
   proname => 'pg_stat_get_archiver', proisstrict => 'f', provolatile => 's',
   proparallel => 'r', prorettype => 'record', proargtypes => '',
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index af7d8fd1e7..1903ad60f8 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -724,6 +724,9 @@ typedef struct EState
 	 */
 	List	   *es_insert_pending_result_relations;
 	List	   *es_insert_pending_modifytables;
+
+	int			es_workers_launched;
+	int			es_workers_planned;
 } EState;
 
 
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index f63159c55c..bad74a9f2d 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -383,6 +383,11 @@ typedef struct PgStat_StatDBEntry
 	PgStat_Counter sessions_fatal;
 	PgStat_Counter sessions_killed;
 
+	PgStat_Counter parallel_workers_planned;
+	PgStat_Counter parallel_workers_launched;
+	PgStat_Counter parallel_maint_workers_planned;
+	PgStat_Counter parallel_maint_workers_launched;
+
 	TimestampTz stat_reset_timestamp;
 } PgStat_StatDBEntry;
 
@@ -578,6 +583,8 @@ extern void pgstat_report_deadlock(void);
 extern void pgstat_report_checksum_failures_in_db(Oid dboid, int failurecount);
 extern void pgstat_report_checksum_failure(void);
 extern void pgstat_report_connect(Oid dboid);
+extern void pgstat_update_parallel_workers_stats(PgStat_Counter parallel_workers_planned, PgStat_Counter parallel_workers_launched);
+extern void pgstat_update_parallel_maint_workers_stats(PgStat_Counter parallel_maint_workers_planned, PgStat_Counter parallel_maint_workers_launched);
 
 #define pgstat_count_buffer_read_time(n)							\
 	(pgStatBlockReadTime += (n))
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 862433ee52..e8a4453cd5 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1861,6 +1861,10 @@ pg_stat_database| SELECT oid AS datid,
     pg_stat_get_db_sessions_abandoned(oid) AS sessions_abandoned,
     pg_stat_get_db_sessions_fatal(oid) AS sessions_fatal,
     pg_stat_get_db_sessions_killed(oid) AS sessions_killed,
+    pg_stat_get_db_parallel_workers_planned(oid) AS parallel_workers_planned,
+    pg_stat_get_db_parallel_workers_launched(oid) AS parallel_workers_launched,
+    pg_stat_get_db_parallel_maint_workers_planned(oid) AS parallel_maint_workers_planned,
+    pg_stat_get_db_parallel_maint_workers_launched(oid) AS parallel_maint_workers_launched,
     pg_stat_get_db_stat_reset_time(oid) AS stats_reset
    FROM ( SELECT 0 AS oid,
             NULL::name AS datname
diff --git a/src/test/regress/expected/stats.out b/src/test/regress/expected/stats.out
index 6e08898b18..88d283a991 100644
--- a/src/test/regress/expected/stats.out
+++ b/src/test/regress/expected/stats.out
@@ -32,6 +32,11 @@ SELECT t.seq_scan, t.seq_tup_read, t.idx_scan, t.idx_tup_fetch,
        pg_catalog.pg_statio_user_tables AS b
  WHERE t.relname='tenk2' AND b.relname='tenk2';
 COMMIT;
+SELECT sum(parallel_workers_planned) AS parallel_workers_planned_before,
+       sum(parallel_workers_launched) AS parallel_workers_launched_before,
+       sum(parallel_maint_workers_planned) AS parallel_maint_workers_planned_before,
+       sum(parallel_maint_workers_launched) AS parallel_maint_workers_launched_before
+FROM pg_stat_database \gset
 -- test effects of TRUNCATE on n_live_tup/n_dead_tup counters
 CREATE TABLE trunc_stats_test(id serial);
 CREATE TABLE trunc_stats_test1(id serial, stuff text);
@@ -862,6 +867,18 @@ WHERE pg_stat_get_backend_pid(beid) = pg_backend_pid();
  t
 (1 row)
 
+-- Test that parallel workers stats are updated in pg_stat_database
+SELECT
+  sum(parallel_workers_planned) > :'parallel_workers_planned_before' AS wrk_planned,
+  sum(parallel_workers_launched) > :'parallel_workers_launched_before' AS wrk_launched,
+  sum(parallel_maint_workers_planned) > :'parallel_maint_workers_planned_before' AS maint_wrk_planned,
+  sum(parallel_maint_workers_launched) > :'parallel_maint_workers_launched_before' AS maint_wrk_launched
+FROM pg_stat_database;
+ wrk_planned | wrk_launched | maint_wrk_planned | maint_wrk_launched 
+-------------+--------------+-------------------+--------------------
+ t           | t            | t                 | t
+(1 row)
+
 -----
 -- Test that resetting stats works for reset timestamp
 -----
diff --git a/src/test/regress/sql/stats.sql b/src/test/regress/sql/stats.sql
index d8ac0d06f4..3a59c75539 100644
--- a/src/test/regress/sql/stats.sql
+++ b/src/test/regress/sql/stats.sql
@@ -32,6 +32,12 @@ SELECT t.seq_scan, t.seq_tup_read, t.idx_scan, t.idx_tup_fetch,
  WHERE t.relname='tenk2' AND b.relname='tenk2';
 COMMIT;
 
+SELECT sum(parallel_workers_planned) AS parallel_workers_planned_before,
+       sum(parallel_workers_launched) AS parallel_workers_launched_before,
+       sum(parallel_maint_workers_planned) AS parallel_maint_workers_planned_before,
+       sum(parallel_maint_workers_launched) AS parallel_maint_workers_launched_before
+FROM pg_stat_database \gset
+
 -- test effects of TRUNCATE on n_live_tup/n_dead_tup counters
 CREATE TABLE trunc_stats_test(id serial);
 CREATE TABLE trunc_stats_test1(id serial, stuff text);
@@ -442,6 +448,14 @@ SELECT (current_schemas(true))[1] = ('pg_temp_' || beid::text) AS match
 FROM pg_stat_get_backend_idset() beid
 WHERE pg_stat_get_backend_pid(beid) = pg_backend_pid();
 
+-- Test that parallel workers stats are updated in pg_stat_database
+SELECT
+  sum(parallel_workers_planned) > :'parallel_workers_planned_before' AS wrk_planned,
+  sum(parallel_workers_launched) > :'parallel_workers_launched_before' AS wrk_launched,
+  sum(parallel_maint_workers_planned) > :'parallel_maint_workers_planned_before' AS maint_wrk_planned,
+  sum(parallel_maint_workers_launched) > :'parallel_maint_workers_launched_before' AS maint_wrk_launched
+FROM pg_stat_database;
+
 -----
 -- Test that resetting stats works for reset timestamp
 -----
-- 
2.45.2

From 1b52f5fb4e977599b8925c69193d31148042ca7d Mon Sep 17 00:00:00 2001
From: benoit <benoit.lobreau@dalibo.com>
Date: Wed, 28 Aug 2024 02:27:13 +0200
Subject: [PATCH] Adds four parallel workers stat columns to pg_stat_database

* parallel_workers_planned
* parallel_workers_launched
* parallel_maint_workers_planned
* parallel_maint_workers_launched
---
 doc/src/sgml/monitoring.sgml                  | 36 +++++++++++++++++++
 src/backend/access/brin/brin.c                |  4 +++
 src/backend/access/nbtree/nbtsort.c           |  4 +++
 src/backend/catalog/system_views.sql          |  4 +++
 src/backend/commands/vacuumparallel.c         |  5 +++
 src/backend/executor/execMain.c               |  7 ++++
 src/backend/executor/execUtils.c              |  3 ++
 src/backend/executor/nodeGather.c             |  3 ++
 src/backend/executor/nodeGatherMerge.c        |  3 ++
 src/backend/utils/activity/pgstat_database.c  | 36 +++++++++++++++++++
 src/backend/utils/adt/pgstatfuncs.c           | 12 +++++++
 src/include/catalog/pg_proc.dat               | 20 +++++++++++
 src/include/nodes/execnodes.h                 |  3 ++
 src/include/pgstat.h                          |  7 ++++
 src/test/regress/expected/rules.out           |  4 +++
 src/test/regress/expected/select_parallel.out | 27 ++++++++++++++
 src/test/regress/expected/vacuum_parallel.out | 19 ++++++++++
 src/test/regress/sql/select_parallel.sql      | 15 ++++++++
 src/test/regress/sql/vacuum_parallel.sql      | 11 ++++++
 19 files changed, 223 insertions(+)

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 55417a6fa9..8c4b11c11d 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3508,6 +3508,42 @@ description | Waiting for a newly initialized WAL file to reach durable storage
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_workers_planned</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers planned by queries on this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_workers_launched</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers obtained by queries on this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_maint_workers_planned</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers planned by utilities on this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_maint_workers_launched</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers obtained by utilities on this database
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c
index 6467bed604..9eceb87b52 100644
--- a/src/backend/access/brin/brin.c
+++ b/src/backend/access/brin/brin.c
@@ -2540,6 +2540,10 @@ _brin_end_parallel(BrinLeader *brinleader, BrinBuildState *state)
 	/* Shutdown worker processes */
 	WaitForParallelWorkersToFinish(brinleader->pcxt);
 
+	pgstat_update_parallel_maint_workers_stats(
+		(PgStat_Counter) brinleader->pcxt->nworkers_to_launch,
+		(PgStat_Counter) brinleader->pcxt->nworkers_launched);
+
 	/*
 	 * Next, accumulate WAL usage.  (This must wait for the workers to finish,
 	 * or we might get incomplete data.)
diff --git a/src/backend/access/nbtree/nbtsort.c b/src/backend/access/nbtree/nbtsort.c
index f5d7b3b0c3..232e1a0942 100644
--- a/src/backend/access/nbtree/nbtsort.c
+++ b/src/backend/access/nbtree/nbtsort.c
@@ -1611,6 +1611,10 @@ _bt_end_parallel(BTLeader *btleader)
 	/* Shutdown worker processes */
 	WaitForParallelWorkersToFinish(btleader->pcxt);
 
+	pgstat_update_parallel_maint_workers_stats(
+		(PgStat_Counter) btleader->pcxt->nworkers_to_launch,
+		(PgStat_Counter) btleader->pcxt->nworkers_launched);
+
 	/*
 	 * Next, accumulate WAL usage.  (This must wait for the workers to finish,
 	 * or we might get incomplete data.)
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 19cabc9a47..48bf9e5535 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1073,6 +1073,10 @@ CREATE VIEW pg_stat_database AS
             pg_stat_get_db_sessions_abandoned(D.oid) AS sessions_abandoned,
             pg_stat_get_db_sessions_fatal(D.oid) AS sessions_fatal,
             pg_stat_get_db_sessions_killed(D.oid) AS sessions_killed,
+            pg_stat_get_db_parallel_workers_planned(D.oid) as parallel_workers_planned,
+            pg_stat_get_db_parallel_workers_launched(D.oid) as parallel_workers_launched,
+            pg_stat_get_db_parallel_maint_workers_planned(D.oid) as parallel_maint_workers_planned,
+            pg_stat_get_db_parallel_maint_workers_launched(D.oid) as parallel_maint_workers_launched,
             pg_stat_get_db_stat_reset_time(D.oid) AS stats_reset
     FROM (
         SELECT 0 AS oid, NULL::name AS datname
diff --git a/src/backend/commands/vacuumparallel.c b/src/backend/commands/vacuumparallel.c
index 22c057fe61..e3a64290e5 100644
--- a/src/backend/commands/vacuumparallel.c
+++ b/src/backend/commands/vacuumparallel.c
@@ -737,6 +737,11 @@ parallel_vacuum_process_all_indexes(ParallelVacuumState *pvs, int num_index_scan
 
 		for (int i = 0; i < pvs->pcxt->nworkers_launched; i++)
 			InstrAccumParallelQuery(&pvs->buffer_usage[i], &pvs->wal_usage[i]);
+
+		pgstat_update_parallel_maint_workers_stats(
+			(PgStat_Counter) pvs->pcxt->nworkers_to_launch,
+			(PgStat_Counter) pvs->pcxt->nworkers_launched
+		);
 	}
 
 	/*
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index 29e186fa73..9bf5f57b65 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -51,6 +51,7 @@
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
 #include "parser/parse_relation.h"
+#include "pgstat.h"
 #include "rewrite/rewriteHandler.h"
 #include "tcop/utility.h"
 #include "utils/acl.h"
@@ -480,6 +481,12 @@ standard_ExecutorEnd(QueryDesc *queryDesc)
 
 	Assert(estate != NULL);
 
+	if (estate->es_workers_planned > 0) {
+		pgstat_update_parallel_workers_stats(
+			(PgStat_Counter) estate->es_workers_planned,
+			(PgStat_Counter) estate->es_workers_launched);
+	}
+
 	/*
 	 * Check that ExecutorFinish was called, unless in EXPLAIN-only mode. This
 	 * Assert is needed because ExecutorFinish is new as of 9.1, and callers
diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
index 5737f9f4eb..5919902075 100644
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -162,6 +162,9 @@ CreateExecutorState(void)
 	estate->es_jit_flags = 0;
 	estate->es_jit = NULL;
 
+	estate->es_workers_launched = 0;
+	estate->es_workers_planned = 0;
+
 	/*
 	 * Return the executor state structure
 	 */
diff --git a/src/backend/executor/nodeGather.c b/src/backend/executor/nodeGather.c
index 5d4ffe989c..1271a0f7d1 100644
--- a/src/backend/executor/nodeGather.c
+++ b/src/backend/executor/nodeGather.c
@@ -182,6 +182,9 @@ ExecGather(PlanState *pstate)
 			/* We save # workers launched for the benefit of EXPLAIN */
 			node->nworkers_launched = pcxt->nworkers_launched;
 
+			estate->es_workers_launched += pcxt->nworkers_launched;
+			estate->es_workers_planned += pcxt->nworkers_to_launch;
+
 			/* 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 45f6017c29..677c450c3d 100644
--- a/src/backend/executor/nodeGatherMerge.c
+++ b/src/backend/executor/nodeGatherMerge.c
@@ -223,6 +223,9 @@ ExecGatherMerge(PlanState *pstate)
 			/* We save # workers launched for the benefit of EXPLAIN */
 			node->nworkers_launched = pcxt->nworkers_launched;
 
+			estate->es_workers_launched += pcxt->nworkers_launched;
+			estate->es_workers_planned += pcxt->nworkers_to_launch;
+
 			/* Set up tuple queue readers to read the results. */
 			if (pcxt->nworkers_launched > 0)
 			{
diff --git a/src/backend/utils/activity/pgstat_database.c b/src/backend/utils/activity/pgstat_database.c
index 29bc090974..9e72c286b2 100644
--- a/src/backend/utils/activity/pgstat_database.c
+++ b/src/backend/utils/activity/pgstat_database.c
@@ -262,6 +262,38 @@ AtEOXact_PgStat_Database(bool isCommit, bool parallel)
 	}
 }
 
+/*
+ * reports parallel_workers_planned and parallel_workers_launched into
+ * PgStat_StatDBEntry
+ */
+void
+pgstat_update_parallel_workers_stats(PgStat_Counter parallel_workers_planned, PgStat_Counter parallel_workers_launched)
+{
+	PgStat_StatDBEntry *dbentry;
+	if (!OidIsValid(MyDatabaseId))
+		return;
+
+	dbentry = pgstat_prep_database_pending(MyDatabaseId);
+	dbentry->parallel_workers_planned += parallel_workers_planned;
+	dbentry->parallel_workers_launched += parallel_workers_launched;
+}
+
+/*
+ * reports parallel_maint_workers_planned and parallel_maint_workers_launched into
+ * PgStat_StatDBEntry
+ */
+void
+pgstat_update_parallel_maint_workers_stats(PgStat_Counter parallel_maint_workers_planned, PgStat_Counter parallel_maint_workers_launched)
+{
+	PgStat_StatDBEntry *dbentry;
+	if (!OidIsValid(MyDatabaseId))
+		return;
+
+	dbentry = pgstat_prep_database_pending(MyDatabaseId);
+	dbentry->parallel_maint_workers_planned += parallel_maint_workers_planned;
+	dbentry->parallel_maint_workers_launched += parallel_maint_workers_launched;
+}
+
 /*
  * Subroutine for pgstat_report_stat(): Handle xact commit/rollback and I/O
  * timings.
@@ -425,6 +457,10 @@ pgstat_database_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
 	PGSTAT_ACCUM_DBCOUNT(sessions_abandoned);
 	PGSTAT_ACCUM_DBCOUNT(sessions_fatal);
 	PGSTAT_ACCUM_DBCOUNT(sessions_killed);
+	PGSTAT_ACCUM_DBCOUNT(parallel_workers_planned);
+	PGSTAT_ACCUM_DBCOUNT(parallel_workers_launched);
+	PGSTAT_ACCUM_DBCOUNT(parallel_maint_workers_planned);
+	PGSTAT_ACCUM_DBCOUNT(parallel_maint_workers_launched);
 #undef PGSTAT_ACCUM_DBCOUNT
 
 	pgstat_unlock_entry(entry_ref);
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 3221137123..377a0f6453 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1039,6 +1039,18 @@ PG_STAT_GET_DBENTRY_INT64(sessions_fatal)
 /* pg_stat_get_db_sessions_killed */
 PG_STAT_GET_DBENTRY_INT64(sessions_killed)
 
+/* pg_stat_get_db_parallel_workers_planned*/
+PG_STAT_GET_DBENTRY_INT64(parallel_workers_planned)
+
+/* pg_stat_get_db_parallel_workers_launched*/
+PG_STAT_GET_DBENTRY_INT64(parallel_workers_launched)
+
+/* pg_stat_get_db_parallel_maint_workers_planned*/
+PG_STAT_GET_DBENTRY_INT64(parallel_maint_workers_planned)
+
+/* pg_stat_get_db_parallel_maint_workers_launched*/
+PG_STAT_GET_DBENTRY_INT64(parallel_maint_workers_launched)
+
 /* pg_stat_get_db_temp_bytes */
 PG_STAT_GET_DBENTRY_INT64(temp_bytes)
 
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 4abc6d9526..b1cd4fa1b0 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5751,6 +5751,26 @@
   proname => 'pg_stat_get_db_sessions_killed', provolatile => 's',
   proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
   prosrc => 'pg_stat_get_db_sessions_killed' },
+{ oid => '8403',
+  descr => 'statistics: number of parallel workers planned for queries',
+  proname => 'pg_stat_get_db_parallel_workers_planned', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_workers_planned' },
+{ oid => '8404',
+  descr => 'statistics: number of parallel workers effectively launched for queries',
+  proname => 'pg_stat_get_db_parallel_workers_launched', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_workers_launched' },
+{ oid => '8405',
+  descr => 'statistics: number of parallel workers planned for utilities',
+  proname => 'pg_stat_get_db_parallel_maint_workers_planned', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_maint_workers_planned' },
+{ oid => '8406',
+  descr => 'statistics: number of parallel workers effectively launched for utilities',
+  proname => 'pg_stat_get_db_parallel_maint_workers_launched', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_maint_workers_launched' },
 { oid => '3195', descr => 'statistics: information about WAL archiver',
   proname => 'pg_stat_get_archiver', proisstrict => 'f', provolatile => 's',
   proparallel => 'r', prorettype => 'record', proargtypes => '',
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index af7d8fd1e7..1903ad60f8 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -724,6 +724,9 @@ typedef struct EState
 	 */
 	List	   *es_insert_pending_result_relations;
 	List	   *es_insert_pending_modifytables;
+
+	int			es_workers_launched;
+	int			es_workers_planned;
 } EState;
 
 
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index f63159c55c..bad74a9f2d 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -383,6 +383,11 @@ typedef struct PgStat_StatDBEntry
 	PgStat_Counter sessions_fatal;
 	PgStat_Counter sessions_killed;
 
+	PgStat_Counter parallel_workers_planned;
+	PgStat_Counter parallel_workers_launched;
+	PgStat_Counter parallel_maint_workers_planned;
+	PgStat_Counter parallel_maint_workers_launched;
+
 	TimestampTz stat_reset_timestamp;
 } PgStat_StatDBEntry;
 
@@ -578,6 +583,8 @@ extern void pgstat_report_deadlock(void);
 extern void pgstat_report_checksum_failures_in_db(Oid dboid, int failurecount);
 extern void pgstat_report_checksum_failure(void);
 extern void pgstat_report_connect(Oid dboid);
+extern void pgstat_update_parallel_workers_stats(PgStat_Counter parallel_workers_planned, PgStat_Counter parallel_workers_launched);
+extern void pgstat_update_parallel_maint_workers_stats(PgStat_Counter parallel_maint_workers_planned, PgStat_Counter parallel_maint_workers_launched);
 
 #define pgstat_count_buffer_read_time(n)							\
 	(pgStatBlockReadTime += (n))
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 862433ee52..e8a4453cd5 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1861,6 +1861,10 @@ pg_stat_database| SELECT oid AS datid,
     pg_stat_get_db_sessions_abandoned(oid) AS sessions_abandoned,
     pg_stat_get_db_sessions_fatal(oid) AS sessions_fatal,
     pg_stat_get_db_sessions_killed(oid) AS sessions_killed,
+    pg_stat_get_db_parallel_workers_planned(oid) AS parallel_workers_planned,
+    pg_stat_get_db_parallel_workers_launched(oid) AS parallel_workers_launched,
+    pg_stat_get_db_parallel_maint_workers_planned(oid) AS parallel_maint_workers_planned,
+    pg_stat_get_db_parallel_maint_workers_launched(oid) AS parallel_maint_workers_launched,
     pg_stat_get_db_stat_reset_time(oid) AS stats_reset
    FROM ( SELECT 0 AS oid,
             NULL::name AS datname
diff --git a/src/test/regress/expected/select_parallel.out b/src/test/regress/expected/select_parallel.out
index c565407082..7c196a38f4 100644
--- a/src/test/regress/expected/select_parallel.out
+++ b/src/test/regress/expected/select_parallel.out
@@ -1,6 +1,17 @@
 --
 -- PARALLEL
 --
+-- Get a reference for parallel stats in pg_stat_database
+select pg_stat_force_next_flush();
+ pg_stat_force_next_flush 
+--------------------------
+ 
+(1 row)
+
+select parallel_workers_planned as parallel_workers_planned_before,
+       parallel_workers_launched as parallel_workers_launched_before
+from pg_stat_database
+where datname = 'regression' \gset
 create function sp_parallel_restricted(int) returns int as
   $$begin return $1; end$$ language plpgsql parallel restricted;
 begin;
@@ -1386,3 +1397,19 @@ reset debug_parallel_query;
 drop function set_and_report_role();
 drop function set_role_and_error(int);
 drop role regress_parallel_worker;
+-- Check parallel stats in pg_stat_database
+select pg_stat_force_next_flush();
+ pg_stat_force_next_flush 
+--------------------------
+ 
+(1 row)
+
+select :'parallel_workers_planned_before' < parallel_workers_planned as wrk_planned_changed,
+       :'parallel_workers_launched_before' < parallel_workers_launched as wrk_launched_changed
+from pg_stat_database
+where datname = 'regression';
+ wrk_planned_changed | wrk_launched_changed 
+---------------------+----------------------
+ t                   | t
+(1 row)
+
diff --git a/src/test/regress/expected/vacuum_parallel.out b/src/test/regress/expected/vacuum_parallel.out
index ddf0ee544b..4c9c5cb1fd 100644
--- a/src/test/regress/expected/vacuum_parallel.out
+++ b/src/test/regress/expected/vacuum_parallel.out
@@ -37,9 +37,28 @@ WHERE oid in ('regular_sized_index'::regclass, 'typically_sized_index'::regclass
                                 2
 (1 row)
 
+-- Get a reference for parallel stats in pg_stat_database
+SELECT sum(parallel_maint_workers_planned) AS parallel_maint_workers_planned_before,
+       sum(parallel_maint_workers_launched) AS parallel_maint_workers_launched_before
+FROM pg_stat_database \gset
 -- Parallel VACUUM with B-Tree page deletions, ambulkdelete calls:
 DELETE FROM parallel_vacuum_table;
 VACUUM (PARALLEL 4, INDEX_CLEANUP ON) parallel_vacuum_table;
+-- Check parallel stats in pg_stat_database
+SELECT pg_stat_force_next_flush();
+ pg_stat_force_next_flush 
+--------------------------
+ 
+(1 row)
+
+SELECT sum(parallel_maint_workers_planned) > :'parallel_maint_workers_planned_before' AS maint_wrk_planned,
+       sum(parallel_maint_workers_launched) > :'parallel_maint_workers_launched_before' AS maint_wrk_launched
+FROM pg_stat_database;
+ maint_wrk_planned | maint_wrk_launched 
+-------------------+--------------------
+ t                 | t
+(1 row)
+
 -- Since vacuum_in_leader_small_index uses deduplication, we expect an
 -- assertion failure with bug #17245 (in the absence of bugfix):
 INSERT INTO parallel_vacuum_table SELECT i FROM generate_series(1, 10000) i;
diff --git a/src/test/regress/sql/select_parallel.sql b/src/test/regress/sql/select_parallel.sql
index 22384b5ad8..dd96446b0d 100644
--- a/src/test/regress/sql/select_parallel.sql
+++ b/src/test/regress/sql/select_parallel.sql
@@ -2,6 +2,14 @@
 -- PARALLEL
 --
 
+-- Get a reference for parallel stats in pg_stat_database
+select pg_stat_force_next_flush();
+select parallel_workers_planned as parallel_workers_planned_before,
+       parallel_workers_launched as parallel_workers_launched_before
+from pg_stat_database
+where datname = 'regression' \gset
+
+
 create function sp_parallel_restricted(int) returns int as
   $$begin return $1; end$$ language plpgsql parallel restricted;
 
@@ -543,3 +551,10 @@ reset debug_parallel_query;
 drop function set_and_report_role();
 drop function set_role_and_error(int);
 drop role regress_parallel_worker;
+
+-- Check parallel stats in pg_stat_database
+select pg_stat_force_next_flush();
+select :'parallel_workers_planned_before' < parallel_workers_planned as wrk_planned_changed,
+       :'parallel_workers_launched_before' < parallel_workers_launched as wrk_launched_changed
+from pg_stat_database
+where datname = 'regression';
diff --git a/src/test/regress/sql/vacuum_parallel.sql b/src/test/regress/sql/vacuum_parallel.sql
index 1d23f33e39..d0d7851e6a 100644
--- a/src/test/regress/sql/vacuum_parallel.sql
+++ b/src/test/regress/sql/vacuum_parallel.sql
@@ -31,10 +31,21 @@ WHERE oid in ('regular_sized_index'::regclass, 'typically_sized_index'::regclass
   pg_relation_size(oid) >=
   pg_size_bytes(current_setting('min_parallel_index_scan_size'));
 
+-- Get a reference for parallel stats in pg_stat_database
+SELECT sum(parallel_maint_workers_planned) AS parallel_maint_workers_planned_before,
+       sum(parallel_maint_workers_launched) AS parallel_maint_workers_launched_before
+FROM pg_stat_database \gset
+
 -- Parallel VACUUM with B-Tree page deletions, ambulkdelete calls:
 DELETE FROM parallel_vacuum_table;
 VACUUM (PARALLEL 4, INDEX_CLEANUP ON) parallel_vacuum_table;
 
+-- Check parallel stats in pg_stat_database
+SELECT pg_stat_force_next_flush();
+SELECT sum(parallel_maint_workers_planned) > :'parallel_maint_workers_planned_before' AS maint_wrk_planned,
+       sum(parallel_maint_workers_launched) > :'parallel_maint_workers_launched_before' AS maint_wrk_launched
+FROM pg_stat_database;
+
 -- Since vacuum_in_leader_small_index uses deduplication, we expect an
 -- assertion failure with bug #17245 (in the absence of bugfix):
 INSERT INTO parallel_vacuum_table SELECT i FROM generate_series(1, 10000) i;
-- 
2.45.2

From 9413829616bdc0806970647c15d7d6bbd96489d1 Mon Sep 17 00:00:00 2001
From: Guillaume Lelarge <guillaume.lelarge@dalibo.com>
Date: Mon, 7 Oct 2024 08:45:36 +0200
Subject: [PATCH v5 1/2] Introduce two new counters in EState

They will be used by two other patchs to populate new columns in
pg_stat_database and pg_statements.
---
 src/backend/executor/execUtils.c       | 3 +++
 src/backend/executor/nodeGather.c      | 3 +++
 src/backend/executor/nodeGatherMerge.c | 3 +++
 src/include/nodes/execnodes.h          | 3 +++
 4 files changed, 12 insertions(+)

diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
index 5737f9f4eb..1908481999 100644
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -162,6 +162,9 @@ CreateExecutorState(void)
 	estate->es_jit_flags = 0;
 	estate->es_jit = NULL;
 
+	estate->es_parallelized_workers_launched = 0;
+	estate->es_parallelized_workers_planned = 0;
+
 	/*
 	 * Return the executor state structure
 	 */
diff --git a/src/backend/executor/nodeGather.c b/src/backend/executor/nodeGather.c
index 5d4ffe989c..0fb915175a 100644
--- a/src/backend/executor/nodeGather.c
+++ b/src/backend/executor/nodeGather.c
@@ -182,6 +182,9 @@ ExecGather(PlanState *pstate)
 			/* We save # workers launched for the benefit of EXPLAIN */
 			node->nworkers_launched = pcxt->nworkers_launched;
 
+			estate->es_parallelized_workers_launched += pcxt->nworkers_launched;
+			estate->es_parallelized_workers_planned += pcxt->nworkers_to_launch;
+
 			/* 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 45f6017c29..149ab23d90 100644
--- a/src/backend/executor/nodeGatherMerge.c
+++ b/src/backend/executor/nodeGatherMerge.c
@@ -223,6 +223,9 @@ ExecGatherMerge(PlanState *pstate)
 			/* We save # workers launched for the benefit of EXPLAIN */
 			node->nworkers_launched = pcxt->nworkers_launched;
 
+			estate->es_parallelized_workers_launched += pcxt->nworkers_launched;
+			estate->es_parallelized_workers_planned += pcxt->nworkers_to_launch;
+
 			/* 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 aab59d681c..f898590ece 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -708,6 +708,9 @@ typedef struct EState
 
 	bool		es_use_parallel_mode;	/* can we use parallel workers? */
 
+	int			es_parallelized_workers_launched;
+	int			es_parallelized_workers_planned;
+
 	/* The per-query shared memory area to use for parallel execution. */
 	struct dsa_area *es_query_dsa;
 
-- 
2.46.2

From 873c03b99e1ccc05bac4c71b5f070e0dbe0bd779 Mon Sep 17 00:00:00 2001
From: benoit <benoit.lobreau@dalibo.com>
Date: Mon, 7 Oct 2024 10:12:46 +0200
Subject: [PATCH v5 2/2] Adds four parallel workers stat columns to
 pg_stat_database

* parallel_workers_planned
* parallel_workers_launched
* parallel_maint_workers_planned
* parallel_maint_workers_launched
---
 doc/src/sgml/monitoring.sgml                  | 36 +++++++++++++++++++
 src/backend/access/brin/brin.c                |  4 +++
 src/backend/access/nbtree/nbtsort.c           |  4 +++
 src/backend/catalog/system_views.sql          |  4 +++
 src/backend/commands/vacuumparallel.c         |  5 +++
 src/backend/executor/execMain.c               |  7 ++++
 src/backend/utils/activity/pgstat_database.c  | 36 +++++++++++++++++++
 src/backend/utils/adt/pgstatfuncs.c           | 12 +++++++
 src/include/catalog/pg_proc.dat               | 20 +++++++++++
 src/include/pgstat.h                          |  7 ++++
 src/test/regress/expected/rules.out           |  4 +++
 src/test/regress/expected/select_parallel.out | 11 ++++++
 src/test/regress/expected/vacuum_parallel.out | 19 ++++++++++
 src/test/regress/sql/select_parallel.sql      |  8 +++++
 src/test/regress/sql/vacuum_parallel.sql      | 11 ++++++
 15 files changed, 188 insertions(+)

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 331315f8d3..9567ca5bd1 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3611,6 +3611,42 @@ description | Waiting for a newly initialized WAL file to reach durable storage
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_workers_planned</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers planned by queries on this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_workers_launched</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers obtained by queries on this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_maint_workers_planned</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers planned by utilities on this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_maint_workers_launched</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers obtained by utilities on this database
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c
index c0b978119a..4e83091d2c 100644
--- a/src/backend/access/brin/brin.c
+++ b/src/backend/access/brin/brin.c
@@ -2544,6 +2544,10 @@ _brin_end_parallel(BrinLeader *brinleader, BrinBuildState *state)
 	/* Shutdown worker processes */
 	WaitForParallelWorkersToFinish(brinleader->pcxt);
 
+	pgstat_update_parallel_maint_workers_stats(
+		(PgStat_Counter) brinleader->pcxt->nworkers_to_launch,
+		(PgStat_Counter) brinleader->pcxt->nworkers_launched);
+
 	/*
 	 * Next, accumulate WAL usage.  (This must wait for the workers to finish,
 	 * or we might get incomplete data.)
diff --git a/src/backend/access/nbtree/nbtsort.c b/src/backend/access/nbtree/nbtsort.c
index 5cca0d4f52..8ee5fcf6d3 100644
--- a/src/backend/access/nbtree/nbtsort.c
+++ b/src/backend/access/nbtree/nbtsort.c
@@ -1615,6 +1615,10 @@ _bt_end_parallel(BTLeader *btleader)
 	/* Shutdown worker processes */
 	WaitForParallelWorkersToFinish(btleader->pcxt);
 
+	pgstat_update_parallel_maint_workers_stats(
+		(PgStat_Counter) btleader->pcxt->nworkers_to_launch,
+		(PgStat_Counter) btleader->pcxt->nworkers_launched);
+
 	/*
 	 * Next, accumulate WAL usage.  (This must wait for the workers to finish,
 	 * or we might get incomplete data.)
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 3456b821bc..7e693a5bae 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1073,6 +1073,10 @@ CREATE VIEW pg_stat_database AS
             pg_stat_get_db_sessions_abandoned(D.oid) AS sessions_abandoned,
             pg_stat_get_db_sessions_fatal(D.oid) AS sessions_fatal,
             pg_stat_get_db_sessions_killed(D.oid) AS sessions_killed,
+            pg_stat_get_db_parallel_workers_planned(D.oid) as parallel_workers_planned,
+            pg_stat_get_db_parallel_workers_launched(D.oid) as parallel_workers_launched,
+            pg_stat_get_db_parallel_maint_workers_planned(D.oid) as parallel_maint_workers_planned,
+            pg_stat_get_db_parallel_maint_workers_launched(D.oid) as parallel_maint_workers_launched,
             pg_stat_get_db_stat_reset_time(D.oid) AS stats_reset
     FROM (
         SELECT 0 AS oid, NULL::name AS datname
diff --git a/src/backend/commands/vacuumparallel.c b/src/backend/commands/vacuumparallel.c
index 4fd6574e12..c6f43419aa 100644
--- a/src/backend/commands/vacuumparallel.c
+++ b/src/backend/commands/vacuumparallel.c
@@ -739,6 +739,11 @@ parallel_vacuum_process_all_indexes(ParallelVacuumState *pvs, int num_index_scan
 
 		for (int i = 0; i < pvs->pcxt->nworkers_launched; i++)
 			InstrAccumParallelQuery(&pvs->buffer_usage[i], &pvs->wal_usage[i]);
+
+		pgstat_update_parallel_maint_workers_stats(
+			(PgStat_Counter) pvs->pcxt->nworkers_to_launch,
+			(PgStat_Counter) pvs->pcxt->nworkers_launched
+		);
 	}
 
 	/*
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index cc9a594cba..e749cdaa17 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -52,6 +52,7 @@
 #include "miscadmin.h"
 #include "nodes/queryjumble.h"
 #include "parser/parse_relation.h"
+#include "pgstat.h"
 #include "rewrite/rewriteHandler.h"
 #include "tcop/utility.h"
 #include "utils/acl.h"
@@ -483,6 +484,12 @@ standard_ExecutorEnd(QueryDesc *queryDesc)
 
 	Assert(estate != NULL);
 
+	if (estate->es_parallelized_workers_planned > 0) {
+		pgstat_update_parallel_workers_stats(
+			(PgStat_Counter) estate->es_parallelized_workers_planned,
+			(PgStat_Counter) estate->es_parallelized_workers_launched);
+	}
+
 	/*
 	 * Check that ExecutorFinish was called, unless in EXPLAIN-only mode. This
 	 * Assert is needed because ExecutorFinish is new as of 9.1, and callers
diff --git a/src/backend/utils/activity/pgstat_database.c b/src/backend/utils/activity/pgstat_database.c
index 29bc090974..9e72c286b2 100644
--- a/src/backend/utils/activity/pgstat_database.c
+++ b/src/backend/utils/activity/pgstat_database.c
@@ -262,6 +262,38 @@ AtEOXact_PgStat_Database(bool isCommit, bool parallel)
 	}
 }
 
+/*
+ * reports parallel_workers_planned and parallel_workers_launched into
+ * PgStat_StatDBEntry
+ */
+void
+pgstat_update_parallel_workers_stats(PgStat_Counter parallel_workers_planned, PgStat_Counter parallel_workers_launched)
+{
+	PgStat_StatDBEntry *dbentry;
+	if (!OidIsValid(MyDatabaseId))
+		return;
+
+	dbentry = pgstat_prep_database_pending(MyDatabaseId);
+	dbentry->parallel_workers_planned += parallel_workers_planned;
+	dbentry->parallel_workers_launched += parallel_workers_launched;
+}
+
+/*
+ * reports parallel_maint_workers_planned and parallel_maint_workers_launched into
+ * PgStat_StatDBEntry
+ */
+void
+pgstat_update_parallel_maint_workers_stats(PgStat_Counter parallel_maint_workers_planned, PgStat_Counter parallel_maint_workers_launched)
+{
+	PgStat_StatDBEntry *dbentry;
+	if (!OidIsValid(MyDatabaseId))
+		return;
+
+	dbentry = pgstat_prep_database_pending(MyDatabaseId);
+	dbentry->parallel_maint_workers_planned += parallel_maint_workers_planned;
+	dbentry->parallel_maint_workers_launched += parallel_maint_workers_launched;
+}
+
 /*
  * Subroutine for pgstat_report_stat(): Handle xact commit/rollback and I/O
  * timings.
@@ -425,6 +457,10 @@ pgstat_database_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
 	PGSTAT_ACCUM_DBCOUNT(sessions_abandoned);
 	PGSTAT_ACCUM_DBCOUNT(sessions_fatal);
 	PGSTAT_ACCUM_DBCOUNT(sessions_killed);
+	PGSTAT_ACCUM_DBCOUNT(parallel_workers_planned);
+	PGSTAT_ACCUM_DBCOUNT(parallel_workers_launched);
+	PGSTAT_ACCUM_DBCOUNT(parallel_maint_workers_planned);
+	PGSTAT_ACCUM_DBCOUNT(parallel_maint_workers_launched);
 #undef PGSTAT_ACCUM_DBCOUNT
 
 	pgstat_unlock_entry(entry_ref);
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index f7b50e0b5a..2db4d2bb6b 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1039,6 +1039,18 @@ PG_STAT_GET_DBENTRY_INT64(sessions_fatal)
 /* pg_stat_get_db_sessions_killed */
 PG_STAT_GET_DBENTRY_INT64(sessions_killed)
 
+/* pg_stat_get_db_parallel_workers_planned*/
+PG_STAT_GET_DBENTRY_INT64(parallel_workers_planned)
+
+/* pg_stat_get_db_parallel_workers_launched*/
+PG_STAT_GET_DBENTRY_INT64(parallel_workers_launched)
+
+/* pg_stat_get_db_parallel_maint_workers_planned*/
+PG_STAT_GET_DBENTRY_INT64(parallel_maint_workers_planned)
+
+/* pg_stat_get_db_parallel_maint_workers_launched*/
+PG_STAT_GET_DBENTRY_INT64(parallel_maint_workers_launched)
+
 /* pg_stat_get_db_temp_bytes */
 PG_STAT_GET_DBENTRY_INT64(temp_bytes)
 
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 77f54a79e6..47dc0f87eb 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5803,6 +5803,26 @@
   proname => 'pg_stat_get_db_sessions_killed', provolatile => 's',
   proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
   prosrc => 'pg_stat_get_db_sessions_killed' },
+{ oid => '8403',
+  descr => 'statistics: number of parallel workers planned for queries',
+  proname => 'pg_stat_get_db_parallel_workers_planned', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_workers_planned' },
+{ oid => '8404',
+  descr => 'statistics: number of parallel workers effectively launched for queries',
+  proname => 'pg_stat_get_db_parallel_workers_launched', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_workers_launched' },
+{ oid => '8405',
+  descr => 'statistics: number of parallel workers planned for utilities',
+  proname => 'pg_stat_get_db_parallel_maint_workers_planned', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_maint_workers_planned' },
+{ oid => '8406',
+  descr => 'statistics: number of parallel workers effectively launched for utilities',
+  proname => 'pg_stat_get_db_parallel_maint_workers_launched', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_maint_workers_launched' },
 { oid => '3195', descr => 'statistics: information about WAL archiver',
   proname => 'pg_stat_get_archiver', proisstrict => 'f', provolatile => 's',
   proparallel => 'r', prorettype => 'record', proargtypes => '',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index df53fa2d4f..1a5c489bbd 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -387,6 +387,11 @@ typedef struct PgStat_StatDBEntry
 	PgStat_Counter sessions_fatal;
 	PgStat_Counter sessions_killed;
 
+	PgStat_Counter parallel_workers_planned;
+	PgStat_Counter parallel_workers_launched;
+	PgStat_Counter parallel_maint_workers_planned;
+	PgStat_Counter parallel_maint_workers_launched;
+
 	TimestampTz stat_reset_timestamp;
 } PgStat_StatDBEntry;
 
@@ -583,6 +588,8 @@ extern void pgstat_report_deadlock(void);
 extern void pgstat_report_checksum_failures_in_db(Oid dboid, int failurecount);
 extern void pgstat_report_checksum_failure(void);
 extern void pgstat_report_connect(Oid dboid);
+extern void pgstat_update_parallel_workers_stats(PgStat_Counter parallel_workers_planned, PgStat_Counter parallel_workers_launched);
+extern void pgstat_update_parallel_maint_workers_stats(PgStat_Counter parallel_maint_workers_planned, PgStat_Counter parallel_maint_workers_launched);
 
 #define pgstat_count_buffer_read_time(n)							\
 	(pgStatBlockReadTime += (n))
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 2b47013f11..c795fb68c1 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1863,6 +1863,10 @@ pg_stat_database| SELECT oid AS datid,
     pg_stat_get_db_sessions_abandoned(oid) AS sessions_abandoned,
     pg_stat_get_db_sessions_fatal(oid) AS sessions_fatal,
     pg_stat_get_db_sessions_killed(oid) AS sessions_killed,
+    pg_stat_get_db_parallel_workers_planned(oid) AS parallel_workers_planned,
+    pg_stat_get_db_parallel_workers_launched(oid) AS parallel_workers_launched,
+    pg_stat_get_db_parallel_maint_workers_planned(oid) AS parallel_maint_workers_planned,
+    pg_stat_get_db_parallel_maint_workers_launched(oid) AS parallel_maint_workers_launched,
     pg_stat_get_db_stat_reset_time(oid) AS stats_reset
    FROM ( SELECT 0 AS oid,
             NULL::name AS datname
diff --git a/src/test/regress/expected/select_parallel.out b/src/test/regress/expected/select_parallel.out
index 2c63aa85a6..db3ca8b198 100644
--- a/src/test/regress/expected/select_parallel.out
+++ b/src/test/regress/expected/select_parallel.out
@@ -1,6 +1,17 @@
 --
 -- PARALLEL
 --
+-- Get a reference for parallel stats in pg_stat_database
+select pg_stat_force_next_flush();
+ pg_stat_force_next_flush 
+--------------------------
+ 
+(1 row)
+
+select parallel_workers_planned as parallel_workers_planned_before,
+       parallel_workers_launched as parallel_workers_launched_before
+from pg_stat_database
+where datname = 'regression' \gset
 create function sp_parallel_restricted(int) returns int as
   $$begin return $1; end$$ language plpgsql parallel restricted;
 begin;
diff --git a/src/test/regress/expected/vacuum_parallel.out b/src/test/regress/expected/vacuum_parallel.out
index ddf0ee544b..4c9c5cb1fd 100644
--- a/src/test/regress/expected/vacuum_parallel.out
+++ b/src/test/regress/expected/vacuum_parallel.out
@@ -37,9 +37,28 @@ WHERE oid in ('regular_sized_index'::regclass, 'typically_sized_index'::regclass
                                 2
 (1 row)
 
+-- Get a reference for parallel stats in pg_stat_database
+SELECT sum(parallel_maint_workers_planned) AS parallel_maint_workers_planned_before,
+       sum(parallel_maint_workers_launched) AS parallel_maint_workers_launched_before
+FROM pg_stat_database \gset
 -- Parallel VACUUM with B-Tree page deletions, ambulkdelete calls:
 DELETE FROM parallel_vacuum_table;
 VACUUM (PARALLEL 4, INDEX_CLEANUP ON) parallel_vacuum_table;
+-- Check parallel stats in pg_stat_database
+SELECT pg_stat_force_next_flush();
+ pg_stat_force_next_flush 
+--------------------------
+ 
+(1 row)
+
+SELECT sum(parallel_maint_workers_planned) > :'parallel_maint_workers_planned_before' AS maint_wrk_planned,
+       sum(parallel_maint_workers_launched) > :'parallel_maint_workers_launched_before' AS maint_wrk_launched
+FROM pg_stat_database;
+ maint_wrk_planned | maint_wrk_launched 
+-------------------+--------------------
+ t                 | t
+(1 row)
+
 -- Since vacuum_in_leader_small_index uses deduplication, we expect an
 -- assertion failure with bug #17245 (in the absence of bugfix):
 INSERT INTO parallel_vacuum_table SELECT i FROM generate_series(1, 10000) i;
diff --git a/src/test/regress/sql/select_parallel.sql b/src/test/regress/sql/select_parallel.sql
index 9ba1328fd2..2ff0f7f21c 100644
--- a/src/test/regress/sql/select_parallel.sql
+++ b/src/test/regress/sql/select_parallel.sql
@@ -2,6 +2,14 @@
 -- PARALLEL
 --
 
+-- Get a reference for parallel stats in pg_stat_database
+select pg_stat_force_next_flush();
+select parallel_workers_planned as parallel_workers_planned_before,
+       parallel_workers_launched as parallel_workers_launched_before
+from pg_stat_database
+where datname = 'regression' \gset
+
+
 create function sp_parallel_restricted(int) returns int as
   $$begin return $1; end$$ language plpgsql parallel restricted;
 
diff --git a/src/test/regress/sql/vacuum_parallel.sql b/src/test/regress/sql/vacuum_parallel.sql
index 1d23f33e39..d0d7851e6a 100644
--- a/src/test/regress/sql/vacuum_parallel.sql
+++ b/src/test/regress/sql/vacuum_parallel.sql
@@ -31,10 +31,21 @@ WHERE oid in ('regular_sized_index'::regclass, 'typically_sized_index'::regclass
   pg_relation_size(oid) >=
   pg_size_bytes(current_setting('min_parallel_index_scan_size'));
 
+-- Get a reference for parallel stats in pg_stat_database
+SELECT sum(parallel_maint_workers_planned) AS parallel_maint_workers_planned_before,
+       sum(parallel_maint_workers_launched) AS parallel_maint_workers_launched_before
+FROM pg_stat_database \gset
+
 -- Parallel VACUUM with B-Tree page deletions, ambulkdelete calls:
 DELETE FROM parallel_vacuum_table;
 VACUUM (PARALLEL 4, INDEX_CLEANUP ON) parallel_vacuum_table;
 
+-- Check parallel stats in pg_stat_database
+SELECT pg_stat_force_next_flush();
+SELECT sum(parallel_maint_workers_planned) > :'parallel_maint_workers_planned_before' AS maint_wrk_planned,
+       sum(parallel_maint_workers_launched) > :'parallel_maint_workers_launched_before' AS maint_wrk_launched
+FROM pg_stat_database;
+
 -- Since vacuum_in_leader_small_index uses deduplication, we expect an
 -- assertion failure with bug #17245 (in the absence of bugfix):
 INSERT INTO parallel_vacuum_table SELECT i FROM generate_series(1, 10000) i;
-- 
2.46.2

diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index e749cdaa17..60a643b08d 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -484,10 +484,10 @@ standard_ExecutorEnd(QueryDesc *queryDesc)
 
 	Assert(estate != NULL);
 
-	if (estate->es_parallelized_workers_planned > 0) {
+	if (estate->es_parallel_workers_to_launch > 0) {
 		pgstat_update_parallel_workers_stats(
-			(PgStat_Counter) estate->es_parallelized_workers_planned,
-			(PgStat_Counter) estate->es_parallelized_workers_launched);
+			(PgStat_Counter) estate->es_parallel_workers_to_launch,
+			(PgStat_Counter) estate->es_parallel_workers_launched);
 	}
 
 	/*

From ab9aa1344f974348638dd3898c944f3d5253374d Mon Sep 17 00:00:00 2001
From: benoit <benoit.lobreau@dalibo.com>
Date: Tue, 8 Oct 2024 10:01:52 +0200
Subject: [PATCH 3/3] Adds two parallel workers stat columns for utilities to
 pg_stat_database

* parallel_maint_workers_to_launch
* parallel_maint_workers_launched
---
 doc/src/sgml/monitoring.sgml                  | 18 ++++++++++++++++++
 src/backend/access/brin/brin.c                |  4 ++++
 src/backend/access/nbtree/nbtsort.c           |  4 ++++
 src/backend/catalog/system_views.sql          |  2 ++
 src/backend/commands/vacuumparallel.c         |  6 ++++++
 src/backend/utils/activity/pgstat_database.c  | 18 ++++++++++++++++++
 src/backend/utils/adt/pgstatfuncs.c           |  6 ++++++
 src/include/catalog/pg_proc.dat               | 10 ++++++++++
 src/include/pgstat.h                          |  3 +++
 src/test/regress/expected/rules.out           |  2 ++
 src/test/regress/expected/vacuum_parallel.out | 19 +++++++++++++++++++
 src/test/regress/sql/vacuum_parallel.sql      | 11 +++++++++++
 12 files changed, 103 insertions(+)

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 840d7f8161..bd4e4b63c7 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3629,6 +3629,24 @@ description | Waiting for a newly initialized WAL file to reach durable storage
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_maint_workers_to_launch</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers planned to be launched by utilities on this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_maint_workers_launched</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers launched by utilities on this database
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c
index c0b978119a..4e83091d2c 100644
--- a/src/backend/access/brin/brin.c
+++ b/src/backend/access/brin/brin.c
@@ -2544,6 +2544,10 @@ _brin_end_parallel(BrinLeader *brinleader, BrinBuildState *state)
 	/* Shutdown worker processes */
 	WaitForParallelWorkersToFinish(brinleader->pcxt);
 
+	pgstat_update_parallel_maint_workers_stats(
+		(PgStat_Counter) brinleader->pcxt->nworkers_to_launch,
+		(PgStat_Counter) brinleader->pcxt->nworkers_launched);
+
 	/*
 	 * Next, accumulate WAL usage.  (This must wait for the workers to finish,
 	 * or we might get incomplete data.)
diff --git a/src/backend/access/nbtree/nbtsort.c b/src/backend/access/nbtree/nbtsort.c
index 5cca0d4f52..8ee5fcf6d3 100644
--- a/src/backend/access/nbtree/nbtsort.c
+++ b/src/backend/access/nbtree/nbtsort.c
@@ -1615,6 +1615,10 @@ _bt_end_parallel(BTLeader *btleader)
 	/* Shutdown worker processes */
 	WaitForParallelWorkersToFinish(btleader->pcxt);
 
+	pgstat_update_parallel_maint_workers_stats(
+		(PgStat_Counter) btleader->pcxt->nworkers_to_launch,
+		(PgStat_Counter) btleader->pcxt->nworkers_launched);
+
 	/*
 	 * Next, accumulate WAL usage.  (This must wait for the workers to finish,
 	 * or we might get incomplete data.)
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index da9a8fe99f..648166bb3b 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1075,6 +1075,8 @@ CREATE VIEW pg_stat_database AS
             pg_stat_get_db_sessions_killed(D.oid) AS sessions_killed,
             pg_stat_get_db_parallel_workers_to_launch(D.oid) as parallel_workers_to_launch,
             pg_stat_get_db_parallel_workers_launched(D.oid) as parallel_workers_launched,
+            pg_stat_get_db_parallel_maint_workers_to_launch(D.oid) as parallel_maint_workers_to_launch,
+            pg_stat_get_db_parallel_maint_workers_launched(D.oid) as parallel_maint_workers_launched,
             pg_stat_get_db_stat_reset_time(D.oid) AS stats_reset
     FROM (
         SELECT 0 AS oid, NULL::name AS datname
diff --git a/src/backend/commands/vacuumparallel.c b/src/backend/commands/vacuumparallel.c
index 77679e8df6..edd0823353 100644
--- a/src/backend/commands/vacuumparallel.c
+++ b/src/backend/commands/vacuumparallel.c
@@ -443,6 +443,12 @@ parallel_vacuum_end(ParallelVacuumState *pvs, IndexBulkDeleteResult **istats)
 {
 	Assert(!IsParallelWorker());
 
+	if (pvs->nworkers_to_launch > 0)
+		pgstat_update_parallel_maint_workers_stats(
+			(PgStat_Counter) pvs->pcxt->nworkers_to_launch,
+			(PgStat_Counter) pvs->pcxt->nworkers_launched
+		);
+
 	/* Copy the updated statistics */
 	for (int i = 0; i < pvs->nindexes; i++)
 	{
diff --git a/src/backend/utils/activity/pgstat_database.c b/src/backend/utils/activity/pgstat_database.c
index efa3d51408..38daf6d978 100644
--- a/src/backend/utils/activity/pgstat_database.c
+++ b/src/backend/utils/activity/pgstat_database.c
@@ -278,6 +278,22 @@ pgstat_update_parallel_workers_stats(PgStat_Counter parallel_workers_to_launch,
 	dbentry->parallel_workers_launched += parallel_workers_launched;
 }
 
+/*
+ * reports parallel_maint_workers_to_launch and parallel_maint_workers_launched into
+ * PgStat_StatDBEntry
+ */
+void
+pgstat_update_parallel_maint_workers_stats(PgStat_Counter parallel_maint_workers_to_launch, PgStat_Counter parallel_maint_workers_launched)
+{
+	PgStat_StatDBEntry *dbentry;
+	if (!OidIsValid(MyDatabaseId))
+		return;
+
+	dbentry = pgstat_prep_database_pending(MyDatabaseId);
+	dbentry->parallel_maint_workers_to_launch += parallel_maint_workers_to_launch;
+	dbentry->parallel_maint_workers_launched += parallel_maint_workers_launched;
+}
+
 /*
  * Subroutine for pgstat_report_stat(): Handle xact commit/rollback and I/O
  * timings.
@@ -443,6 +459,8 @@ pgstat_database_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
 	PGSTAT_ACCUM_DBCOUNT(sessions_killed);
 	PGSTAT_ACCUM_DBCOUNT(parallel_workers_to_launch);
 	PGSTAT_ACCUM_DBCOUNT(parallel_workers_launched);
+	PGSTAT_ACCUM_DBCOUNT(parallel_maint_workers_to_launch);
+	PGSTAT_ACCUM_DBCOUNT(parallel_maint_workers_launched);
 #undef PGSTAT_ACCUM_DBCOUNT
 
 	pgstat_unlock_entry(entry_ref);
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 054c416ab4..13d5ea7a5c 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1045,6 +1045,12 @@ PG_STAT_GET_DBENTRY_INT64(parallel_workers_to_launch)
 /* pg_stat_get_db_parallel_workers_launched*/
 PG_STAT_GET_DBENTRY_INT64(parallel_workers_launched)
 
+/* pg_stat_get_db_parallel_maint_workers_to_launch*/
+PG_STAT_GET_DBENTRY_INT64(parallel_maint_workers_to_launch)
+
+/* pg_stat_get_db_parallel_maint_workers_launched*/
+PG_STAT_GET_DBENTRY_INT64(parallel_maint_workers_launched)
+
 /* pg_stat_get_db_temp_bytes */
 PG_STAT_GET_DBENTRY_INT64(temp_bytes)
 
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index fe05b279f2..16cb46f343 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5820,6 +5820,16 @@
   proname => 'pg_stat_get_db_parallel_workers_launched', provolatile => 's',
   proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
   prosrc => 'pg_stat_get_db_parallel_workers_launched' },
+{ oid => '8405',
+  descr => 'statistics: number of parallel workers planned to be launched for utilities',
+  proname => 'pg_stat_get_db_parallel_maint_workers_to_launch', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_maint_workers_to_launch' },
+{ oid => '8406',
+  descr => 'statistics: number of parallel workers effectively launched for utilities',
+  proname => 'pg_stat_get_db_parallel_maint_workers_launched', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_maint_workers_launched' },
 { oid => '3195', descr => 'statistics: information about WAL archiver',
   proname => 'pg_stat_get_archiver', proisstrict => 'f', provolatile => 's',
   proparallel => 'r', prorettype => 'record', proargtypes => '',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index cfba5615a7..3718d31cf6 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -389,6 +389,8 @@ typedef struct PgStat_StatDBEntry
 
 	PgStat_Counter parallel_workers_to_launch;
 	PgStat_Counter parallel_workers_launched;
+	PgStat_Counter parallel_maint_workers_to_launch;
+	PgStat_Counter parallel_maint_workers_launched;
 
 	TimestampTz stat_reset_timestamp;
 } PgStat_StatDBEntry;
@@ -587,6 +589,7 @@ extern void pgstat_report_checksum_failures_in_db(Oid dboid, int failurecount);
 extern void pgstat_report_checksum_failure(void);
 extern void pgstat_report_connect(Oid dboid);
 extern void pgstat_update_parallel_workers_stats(PgStat_Counter parallel_workers_to_launch, PgStat_Counter parallel_workers_launched);
+extern void pgstat_update_parallel_maint_workers_stats(PgStat_Counter parallel_maint_workers_to_launch, PgStat_Counter parallel_maint_workers_launched);
 
 #define pgstat_count_buffer_read_time(n)							\
 	(pgStatBlockReadTime += (n))
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 3014d047fe..e696baa8f3 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1865,6 +1865,8 @@ pg_stat_database| SELECT oid AS datid,
     pg_stat_get_db_sessions_killed(oid) AS sessions_killed,
     pg_stat_get_db_parallel_workers_to_launch(oid) AS parallel_workers_to_launch,
     pg_stat_get_db_parallel_workers_launched(oid) AS parallel_workers_launched,
+    pg_stat_get_db_parallel_maint_workers_to_launch(oid) AS parallel_maint_workers_to_launch,
+    pg_stat_get_db_parallel_maint_workers_launched(oid) AS parallel_maint_workers_launched,
     pg_stat_get_db_stat_reset_time(oid) AS stats_reset
    FROM ( SELECT 0 AS oid,
             NULL::name AS datname
diff --git a/src/test/regress/expected/vacuum_parallel.out b/src/test/regress/expected/vacuum_parallel.out
index ddf0ee544b..4973c7bdae 100644
--- a/src/test/regress/expected/vacuum_parallel.out
+++ b/src/test/regress/expected/vacuum_parallel.out
@@ -37,9 +37,28 @@ WHERE oid in ('regular_sized_index'::regclass, 'typically_sized_index'::regclass
                                 2
 (1 row)
 
+-- Get a reference for parallel stats in pg_stat_database
+SELECT sum(parallel_maint_workers_to_launch) AS parallel_maint_workers_to_launch_before,
+       sum(parallel_maint_workers_launched) AS parallel_maint_workers_launched_before
+FROM pg_stat_database \gset
 -- Parallel VACUUM with B-Tree page deletions, ambulkdelete calls:
 DELETE FROM parallel_vacuum_table;
 VACUUM (PARALLEL 4, INDEX_CLEANUP ON) parallel_vacuum_table;
+-- Check parallel stats in pg_stat_database
+SELECT pg_stat_force_next_flush();
+ pg_stat_force_next_flush 
+--------------------------
+ 
+(1 row)
+
+SELECT sum(parallel_maint_workers_to_launch) > :'parallel_maint_workers_to_launch_before' AS maint_wrk_to_launch,
+       sum(parallel_maint_workers_launched) > :'parallel_maint_workers_launched_before' AS maint_wrk_launched
+FROM pg_stat_database;
+ maint_wrk_to_launch | maint_wrk_launched 
+---------------------+--------------------
+ t                   | t
+(1 row)
+
 -- Since vacuum_in_leader_small_index uses deduplication, we expect an
 -- assertion failure with bug #17245 (in the absence of bugfix):
 INSERT INTO parallel_vacuum_table SELECT i FROM generate_series(1, 10000) i;
diff --git a/src/test/regress/sql/vacuum_parallel.sql b/src/test/regress/sql/vacuum_parallel.sql
index 1d23f33e39..77ddc807cd 100644
--- a/src/test/regress/sql/vacuum_parallel.sql
+++ b/src/test/regress/sql/vacuum_parallel.sql
@@ -31,10 +31,21 @@ WHERE oid in ('regular_sized_index'::regclass, 'typically_sized_index'::regclass
   pg_relation_size(oid) >=
   pg_size_bytes(current_setting('min_parallel_index_scan_size'));
 
+-- Get a reference for parallel stats in pg_stat_database
+SELECT sum(parallel_maint_workers_to_launch) AS parallel_maint_workers_to_launch_before,
+       sum(parallel_maint_workers_launched) AS parallel_maint_workers_launched_before
+FROM pg_stat_database \gset
+
 -- Parallel VACUUM with B-Tree page deletions, ambulkdelete calls:
 DELETE FROM parallel_vacuum_table;
 VACUUM (PARALLEL 4, INDEX_CLEANUP ON) parallel_vacuum_table;
 
+-- Check parallel stats in pg_stat_database
+SELECT pg_stat_force_next_flush();
+SELECT sum(parallel_maint_workers_to_launch) > :'parallel_maint_workers_to_launch_before' AS maint_wrk_to_launch,
+       sum(parallel_maint_workers_launched) > :'parallel_maint_workers_launched_before' AS maint_wrk_launched
+FROM pg_stat_database;
+
 -- Since vacuum_in_leader_small_index uses deduplication, we expect an
 -- assertion failure with bug #17245 (in the absence of bugfix):
 INSERT INTO parallel_vacuum_table SELECT i FROM generate_series(1, 10000) i;
-- 
2.46.2

From d3319375a66bc9e356c8ad741f047d82a47255e3 Mon Sep 17 00:00:00 2001
From: benoit <benoit.lobreau@dalibo.com>
Date: Fri, 11 Oct 2024 23:56:23 +0200
Subject: [PATCH 2/3] Setup counters for parallel vacuums

This is used by the logging and  pg_stat_database patches.
---
 src/backend/commands/vacuumparallel.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/backend/commands/vacuumparallel.c b/src/backend/commands/vacuumparallel.c
index 4fd6574e12..77679e8df6 100644
--- a/src/backend/commands/vacuumparallel.c
+++ b/src/backend/commands/vacuumparallel.c
@@ -208,6 +208,9 @@ struct ParallelVacuumState
 	int			nindexes_parallel_cleanup;
 	int			nindexes_parallel_condcleanup;
 
+	int			nworkers_to_launch;
+	int			nworkers_launched;
+
 	/* Buffer access strategy used by leader process */
 	BufferAccessStrategy bstrategy;
 
@@ -362,6 +365,9 @@ parallel_vacuum_init(Relation rel, Relation *indrels, int nindexes,
 		if ((vacoptions & VACUUM_OPTION_PARALLEL_COND_CLEANUP) != 0)
 			pvs->nindexes_parallel_condcleanup++;
 	}
+	pvs->nworkers_to_launch = 0;
+	pvs->nworkers_launched = 0;
+
 	shm_toc_insert(pcxt->toc, PARALLEL_VACUUM_KEY_INDEX_STATS, indstats);
 	pvs->indstats = indstats;
 
@@ -739,6 +745,9 @@ parallel_vacuum_process_all_indexes(ParallelVacuumState *pvs, int num_index_scan
 
 		for (int i = 0; i < pvs->pcxt->nworkers_launched; i++)
 			InstrAccumParallelQuery(&pvs->buffer_usage[i], &pvs->wal_usage[i]);
+
+		pvs->nworkers_to_launch += pvs->pcxt->nworkers_to_launch;
+		pvs->nworkers_launched += pvs->pcxt->nworkers_launched;
 	}
 
 	/*
-- 
2.46.2

From f759381fdd2315b9fc3bf7c31f505f80f89a5d90 Mon Sep 17 00:00:00 2001
From: benoit <benoit.lobreau@dalibo.com>
Date: Fri, 11 Oct 2024 17:29:13 +0200
Subject: [PATCH 1/3] Adds two parallel workers stat columns to
 pg_stat_database

* parallel_workers_to_launch
* parallel_workers_launched
---
 doc/src/sgml/monitoring.sgml                  | 18 +++++++++++++
 src/backend/catalog/system_views.sql          |  2 ++
 src/backend/executor/execMain.c               |  6 +++++
 src/backend/utils/activity/pgstat_database.c  | 18 +++++++++++++
 src/backend/utils/adt/pgstatfuncs.c           |  6 +++++
 src/include/catalog/pg_proc.dat               | 10 +++++++
 src/include/pgstat.h                          |  4 +++
 src/test/regress/expected/rules.out           |  2 ++
 src/test/regress/expected/select_parallel.out | 26 +++++++++++++++++++
 src/test/regress/sql/select_parallel.sql      | 13 ++++++++++
 10 files changed, 105 insertions(+)

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 331315f8d3..840d7f8161 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3611,6 +3611,24 @@ description | Waiting for a newly initialized WAL file to reach durable storage
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_workers_to_launch</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers planned to be launched by queries on this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_workers_launched</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers launched by queries on this database
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 3456b821bc..da9a8fe99f 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1073,6 +1073,8 @@ CREATE VIEW pg_stat_database AS
             pg_stat_get_db_sessions_abandoned(D.oid) AS sessions_abandoned,
             pg_stat_get_db_sessions_fatal(D.oid) AS sessions_fatal,
             pg_stat_get_db_sessions_killed(D.oid) AS sessions_killed,
+            pg_stat_get_db_parallel_workers_to_launch(D.oid) as parallel_workers_to_launch,
+            pg_stat_get_db_parallel_workers_launched(D.oid) as parallel_workers_launched,
             pg_stat_get_db_stat_reset_time(D.oid) AS stats_reset
     FROM (
         SELECT 0 AS oid, NULL::name AS datname
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index cc9a594cba..e3da94cb10 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -52,6 +52,7 @@
 #include "miscadmin.h"
 #include "nodes/queryjumble.h"
 #include "parser/parse_relation.h"
+#include "pgstat.h"
 #include "rewrite/rewriteHandler.h"
 #include "tcop/utility.h"
 #include "utils/acl.h"
@@ -483,6 +484,11 @@ standard_ExecutorEnd(QueryDesc *queryDesc)
 
 	Assert(estate != NULL);
 
+	if (estate->es_parallel_workers_to_launch > 0)
+		pgstat_update_parallel_workers_stats(
+			(PgStat_Counter) estate->es_parallel_workers_to_launch,
+			(PgStat_Counter) estate->es_parallel_workers_launched);
+
 	/*
 	 * Check that ExecutorFinish was called, unless in EXPLAIN-only mode. This
 	 * Assert is needed because ExecutorFinish is new as of 9.1, and callers
diff --git a/src/backend/utils/activity/pgstat_database.c b/src/backend/utils/activity/pgstat_database.c
index 29bc090974..efa3d51408 100644
--- a/src/backend/utils/activity/pgstat_database.c
+++ b/src/backend/utils/activity/pgstat_database.c
@@ -262,6 +262,22 @@ AtEOXact_PgStat_Database(bool isCommit, bool parallel)
 	}
 }
 
+/*
+ * reports parallel_workers_to_launch and parallel_workers_launched into
+ * PgStat_StatDBEntry
+ */
+void
+pgstat_update_parallel_workers_stats(PgStat_Counter parallel_workers_to_launch, PgStat_Counter parallel_workers_launched)
+{
+	PgStat_StatDBEntry *dbentry;
+	if (!OidIsValid(MyDatabaseId))
+		return;
+
+	dbentry = pgstat_prep_database_pending(MyDatabaseId);
+	dbentry->parallel_workers_to_launch += parallel_workers_to_launch;
+	dbentry->parallel_workers_launched += parallel_workers_launched;
+}
+
 /*
  * Subroutine for pgstat_report_stat(): Handle xact commit/rollback and I/O
  * timings.
@@ -425,6 +441,8 @@ pgstat_database_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
 	PGSTAT_ACCUM_DBCOUNT(sessions_abandoned);
 	PGSTAT_ACCUM_DBCOUNT(sessions_fatal);
 	PGSTAT_ACCUM_DBCOUNT(sessions_killed);
+	PGSTAT_ACCUM_DBCOUNT(parallel_workers_to_launch);
+	PGSTAT_ACCUM_DBCOUNT(parallel_workers_launched);
 #undef PGSTAT_ACCUM_DBCOUNT
 
 	pgstat_unlock_entry(entry_ref);
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index f7b50e0b5a..054c416ab4 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1039,6 +1039,12 @@ PG_STAT_GET_DBENTRY_INT64(sessions_fatal)
 /* pg_stat_get_db_sessions_killed */
 PG_STAT_GET_DBENTRY_INT64(sessions_killed)
 
+/* pg_stat_get_db_parallel_workers_to_launch*/
+PG_STAT_GET_DBENTRY_INT64(parallel_workers_to_launch)
+
+/* pg_stat_get_db_parallel_workers_launched*/
+PG_STAT_GET_DBENTRY_INT64(parallel_workers_launched)
+
 /* pg_stat_get_db_temp_bytes */
 PG_STAT_GET_DBENTRY_INT64(temp_bytes)
 
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 8876bebde0..fe05b279f2 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5810,6 +5810,16 @@
   proname => 'pg_stat_get_db_sessions_killed', provolatile => 's',
   proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
   prosrc => 'pg_stat_get_db_sessions_killed' },
+{ oid => '8403',
+  descr => 'statistics: number of parallel workers planned to be launched for queries',
+  proname => 'pg_stat_get_db_parallel_workers_to_launch', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_workers_to_launch' },
+{ oid => '8404',
+  descr => 'statistics: number of parallel workers effectively launched for queries',
+  proname => 'pg_stat_get_db_parallel_workers_launched', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_workers_launched' },
 { oid => '3195', descr => 'statistics: information about WAL archiver',
   proname => 'pg_stat_get_archiver', proisstrict => 'f', provolatile => 's',
   proparallel => 'r', prorettype => 'record', proargtypes => '',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index df53fa2d4f..cfba5615a7 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -387,6 +387,9 @@ typedef struct PgStat_StatDBEntry
 	PgStat_Counter sessions_fatal;
 	PgStat_Counter sessions_killed;
 
+	PgStat_Counter parallel_workers_to_launch;
+	PgStat_Counter parallel_workers_launched;
+
 	TimestampTz stat_reset_timestamp;
 } PgStat_StatDBEntry;
 
@@ -583,6 +586,7 @@ extern void pgstat_report_deadlock(void);
 extern void pgstat_report_checksum_failures_in_db(Oid dboid, int failurecount);
 extern void pgstat_report_checksum_failure(void);
 extern void pgstat_report_connect(Oid dboid);
+extern void pgstat_update_parallel_workers_stats(PgStat_Counter parallel_workers_to_launch, PgStat_Counter parallel_workers_launched);
 
 #define pgstat_count_buffer_read_time(n)							\
 	(pgStatBlockReadTime += (n))
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 2b47013f11..3014d047fe 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1863,6 +1863,8 @@ pg_stat_database| SELECT oid AS datid,
     pg_stat_get_db_sessions_abandoned(oid) AS sessions_abandoned,
     pg_stat_get_db_sessions_fatal(oid) AS sessions_fatal,
     pg_stat_get_db_sessions_killed(oid) AS sessions_killed,
+    pg_stat_get_db_parallel_workers_to_launch(oid) AS parallel_workers_to_launch,
+    pg_stat_get_db_parallel_workers_launched(oid) AS parallel_workers_launched,
     pg_stat_get_db_stat_reset_time(oid) AS stats_reset
    FROM ( SELECT 0 AS oid,
             NULL::name AS datname
diff --git a/src/test/regress/expected/select_parallel.out b/src/test/regress/expected/select_parallel.out
index d17ade278b..d1bb0bd61a 100644
--- a/src/test/regress/expected/select_parallel.out
+++ b/src/test/regress/expected/select_parallel.out
@@ -1,6 +1,17 @@
 --
 -- PARALLEL
 --
+-- Get a reference for parallel stats in pg_stat_database
+select pg_stat_force_next_flush();
+ pg_stat_force_next_flush 
+--------------------------
+ 
+(1 row)
+
+select parallel_workers_to_launch as parallel_workers_to_launch_before,
+       parallel_workers_launched as parallel_workers_launched_before
+from pg_stat_database
+where datname = 'regression' \gset
 create function sp_parallel_restricted(int) returns int as
   $$begin return $1; end$$ language plpgsql parallel restricted;
 begin;
@@ -1407,3 +1418,18 @@ CREATE UNIQUE INDEX parallel_hang_idx
 SET debug_parallel_query = on;
 DELETE FROM parallel_hang WHERE 380 <= i AND i <= 420;
 ROLLBACK;
+select pg_stat_force_next_flush();
+ pg_stat_force_next_flush 
+--------------------------
+ 
+(1 row)
+
+select parallel_workers_to_launch > :'parallel_workers_to_launch_before'  AS wrk_to_launch,
+       parallel_workers_launched > :'parallel_workers_launched_before' AS wrk_launched
+from pg_stat_database
+where datname = 'regression';
+ wrk_to_launch | wrk_launched 
+---------------+--------------
+ t             | t
+(1 row)
+
diff --git a/src/test/regress/sql/select_parallel.sql b/src/test/regress/sql/select_parallel.sql
index 9ba1328fd2..5da7d6bcc8 100644
--- a/src/test/regress/sql/select_parallel.sql
+++ b/src/test/regress/sql/select_parallel.sql
@@ -2,6 +2,13 @@
 -- PARALLEL
 --
 
+-- Get a reference for parallel stats in pg_stat_database
+select pg_stat_force_next_flush();
+select parallel_workers_to_launch as parallel_workers_to_launch_before,
+       parallel_workers_launched as parallel_workers_launched_before
+from pg_stat_database
+where datname = 'regression' \gset
+
 create function sp_parallel_restricted(int) returns int as
   $$begin return $1; end$$ language plpgsql parallel restricted;
 
@@ -574,3 +581,9 @@ SET debug_parallel_query = on;
 DELETE FROM parallel_hang WHERE 380 <= i AND i <= 420;
 
 ROLLBACK;
+
+select pg_stat_force_next_flush();
+select parallel_workers_to_launch > :'parallel_workers_to_launch_before'  AS wrk_to_launch,
+       parallel_workers_launched > :'parallel_workers_launched_before' AS wrk_launched
+from pg_stat_database
+where datname = 'regression';
-- 
2.46.2

From 960fbe663d4a6a4594b8121bbf299c72ef2a6ab8 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Fri, 8 Nov 2024 13:00:26 +0900
Subject: [PATCH v7] Add two attributes to pg_stat_database for parallel
 workers activity
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Two attributes are added to pg_stat_database:
* parallel_workers_to_launch, counting the total number of parallel
workers that were planned to be launched.
* parallel_workers_launched, counting the total number of parallel
workers actually launched.

The ratio of both fields can provide hints that there are not enough
slots available when launching parallel workers.

This commit relies on de3a2ea3b264, that has added two fields to EState,
that get incremented when executing Gather or GatherMerge nodes.  The
data now gets pushed to pg_stat_database, which is useful how much a
database faces contention when spawning parallel workers if
pg_stat_statements is not enabled on an instance.

Bump catalog version.

Author: Benoit Lobréau
Discussion: https://postgr.es/m/783bc7f7-659a-42fa-99dd-ee0565644e25@dalibo.com
---
 src/include/catalog/catversion.h              |  2 +-
 src/include/catalog/pg_proc.dat               | 10 +++++++
 src/include/pgstat.h                          |  4 +++
 src/backend/catalog/system_views.sql          |  2 ++
 src/backend/executor/execMain.c               |  5 ++++
 src/backend/utils/activity/pgstat_database.c  | 19 +++++++++++++
 src/backend/utils/adt/pgstatfuncs.c           |  6 +++++
 src/test/regress/expected/rules.out           |  2 ++
 src/test/regress/expected/select_parallel.out | 27 +++++++++++++++++++
 src/test/regress/sql/select_parallel.sql      | 14 ++++++++++
 doc/src/sgml/monitoring.sgml                  | 18 +++++++++++++
 11 files changed, 108 insertions(+), 1 deletion(-)

diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index 2abc523f5c..86436e0356 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202411071
+#define CATALOG_VERSION_NO	202411081
 
 #endif
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index f23321a41f..cbbe8acd38 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5813,6 +5813,16 @@
   proname => 'pg_stat_get_db_sessions_killed', provolatile => 's',
   proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
   prosrc => 'pg_stat_get_db_sessions_killed' },
+{ oid => '8403',
+  descr => 'statistics: number of parallel workers planned to be launched by queries',
+  proname => 'pg_stat_get_db_parallel_workers_to_launch', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_workers_to_launch' },
+{ oid => '8404',
+  descr => 'statistics: number of parallel workers effectively launched by queries',
+  proname => 'pg_stat_get_db_parallel_workers_launched', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_db_parallel_workers_launched' },
 { oid => '3195', descr => 'statistics: information about WAL archiver',
   proname => 'pg_stat_get_archiver', proisstrict => 'f', provolatile => 's',
   proparallel => 'r', prorettype => 'record', proargtypes => '',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index df53fa2d4f..59c28b4aca 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -386,6 +386,8 @@ typedef struct PgStat_StatDBEntry
 	PgStat_Counter sessions_abandoned;
 	PgStat_Counter sessions_fatal;
 	PgStat_Counter sessions_killed;
+	PgStat_Counter parallel_workers_to_launch;
+	PgStat_Counter parallel_workers_launched;
 
 	TimestampTz stat_reset_timestamp;
 } PgStat_StatDBEntry;
@@ -583,6 +585,8 @@ extern void pgstat_report_deadlock(void);
 extern void pgstat_report_checksum_failures_in_db(Oid dboid, int failurecount);
 extern void pgstat_report_checksum_failure(void);
 extern void pgstat_report_connect(Oid dboid);
+extern void pgstat_update_parallel_workers_stats(PgStat_Counter workers_to_launch,
+												 PgStat_Counter workers_launched);
 
 #define pgstat_count_buffer_read_time(n)							\
 	(pgStatBlockReadTime += (n))
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 3456b821bc..da9a8fe99f 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1073,6 +1073,8 @@ CREATE VIEW pg_stat_database AS
             pg_stat_get_db_sessions_abandoned(D.oid) AS sessions_abandoned,
             pg_stat_get_db_sessions_fatal(D.oid) AS sessions_fatal,
             pg_stat_get_db_sessions_killed(D.oid) AS sessions_killed,
+            pg_stat_get_db_parallel_workers_to_launch(D.oid) as parallel_workers_to_launch,
+            pg_stat_get_db_parallel_workers_launched(D.oid) as parallel_workers_launched,
             pg_stat_get_db_stat_reset_time(D.oid) AS stats_reset
     FROM (
         SELECT 0 AS oid, NULL::name AS datname
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index cc9a594cba..5ca856fd27 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -52,6 +52,7 @@
 #include "miscadmin.h"
 #include "nodes/queryjumble.h"
 #include "parser/parse_relation.h"
+#include "pgstat.h"
 #include "rewrite/rewriteHandler.h"
 #include "tcop/utility.h"
 #include "utils/acl.h"
@@ -483,6 +484,10 @@ standard_ExecutorEnd(QueryDesc *queryDesc)
 
 	Assert(estate != NULL);
 
+	if (estate->es_parallel_workers_to_launch > 0)
+		pgstat_update_parallel_workers_stats((PgStat_Counter) estate->es_parallel_workers_to_launch,
+											 (PgStat_Counter) estate->es_parallel_workers_launched);
+
 	/*
 	 * Check that ExecutorFinish was called, unless in EXPLAIN-only mode. This
 	 * Assert is needed because ExecutorFinish is new as of 9.1, and callers
diff --git a/src/backend/utils/activity/pgstat_database.c b/src/backend/utils/activity/pgstat_database.c
index 29bc090974..7757d2ace7 100644
--- a/src/backend/utils/activity/pgstat_database.c
+++ b/src/backend/utils/activity/pgstat_database.c
@@ -262,6 +262,23 @@ AtEOXact_PgStat_Database(bool isCommit, bool parallel)
 	}
 }
 
+/*
+ * Notify the stats system about parallel worker information.
+ */
+void
+pgstat_update_parallel_workers_stats(PgStat_Counter workers_to_launch,
+									 PgStat_Counter workers_launched)
+{
+	PgStat_StatDBEntry *dbentry;
+
+	if (!OidIsValid(MyDatabaseId))
+		return;
+
+	dbentry = pgstat_prep_database_pending(MyDatabaseId);
+	dbentry->parallel_workers_to_launch += workers_to_launch;
+	dbentry->parallel_workers_launched += workers_launched;
+}
+
 /*
  * Subroutine for pgstat_report_stat(): Handle xact commit/rollback and I/O
  * timings.
@@ -425,6 +442,8 @@ pgstat_database_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
 	PGSTAT_ACCUM_DBCOUNT(sessions_abandoned);
 	PGSTAT_ACCUM_DBCOUNT(sessions_fatal);
 	PGSTAT_ACCUM_DBCOUNT(sessions_killed);
+	PGSTAT_ACCUM_DBCOUNT(parallel_workers_to_launch);
+	PGSTAT_ACCUM_DBCOUNT(parallel_workers_launched);
 #undef PGSTAT_ACCUM_DBCOUNT
 
 	pgstat_unlock_entry(entry_ref);
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index f7b50e0b5a..60a397dc56 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1039,6 +1039,12 @@ PG_STAT_GET_DBENTRY_INT64(sessions_fatal)
 /* pg_stat_get_db_sessions_killed */
 PG_STAT_GET_DBENTRY_INT64(sessions_killed)
 
+/* pg_stat_get_db_parallel_workers_to_launch */
+PG_STAT_GET_DBENTRY_INT64(parallel_workers_to_launch)
+
+/* pg_stat_get_db_parallel_workers_launched */
+PG_STAT_GET_DBENTRY_INT64(parallel_workers_launched)
+
 /* pg_stat_get_db_temp_bytes */
 PG_STAT_GET_DBENTRY_INT64(temp_bytes)
 
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 2b47013f11..3014d047fe 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1863,6 +1863,8 @@ pg_stat_database| SELECT oid AS datid,
     pg_stat_get_db_sessions_abandoned(oid) AS sessions_abandoned,
     pg_stat_get_db_sessions_fatal(oid) AS sessions_fatal,
     pg_stat_get_db_sessions_killed(oid) AS sessions_killed,
+    pg_stat_get_db_parallel_workers_to_launch(oid) AS parallel_workers_to_launch,
+    pg_stat_get_db_parallel_workers_launched(oid) AS parallel_workers_launched,
     pg_stat_get_db_stat_reset_time(oid) AS stats_reset
    FROM ( SELECT 0 AS oid,
             NULL::name AS datname
diff --git a/src/test/regress/expected/select_parallel.out b/src/test/regress/expected/select_parallel.out
index d17ade278b..8c31f6460d 100644
--- a/src/test/regress/expected/select_parallel.out
+++ b/src/test/regress/expected/select_parallel.out
@@ -1,6 +1,17 @@
 --
 -- PARALLEL
 --
+-- Save parallel worker stats, used for comparison at the end
+select pg_stat_force_next_flush();
+ pg_stat_force_next_flush 
+--------------------------
+ 
+(1 row)
+
+select parallel_workers_to_launch as parallel_workers_to_launch_before,
+       parallel_workers_launched as parallel_workers_launched_before
+  from pg_stat_database
+  where datname = current_database() \gset
 create function sp_parallel_restricted(int) returns int as
   $$begin return $1; end$$ language plpgsql parallel restricted;
 begin;
@@ -1407,3 +1418,19 @@ CREATE UNIQUE INDEX parallel_hang_idx
 SET debug_parallel_query = on;
 DELETE FROM parallel_hang WHERE 380 <= i AND i <= 420;
 ROLLBACK;
+-- Check parallel worker stats
+select pg_stat_force_next_flush();
+ pg_stat_force_next_flush 
+--------------------------
+ 
+(1 row)
+
+select parallel_workers_to_launch > :'parallel_workers_to_launch_before'  AS wrk_to_launch,
+       parallel_workers_launched > :'parallel_workers_launched_before' AS wrk_launched
+  from pg_stat_database
+  where datname = current_database();
+ wrk_to_launch | wrk_launched 
+---------------+--------------
+ t             | t
+(1 row)
+
diff --git a/src/test/regress/sql/select_parallel.sql b/src/test/regress/sql/select_parallel.sql
index 9ba1328fd2..5b4a6e1088 100644
--- a/src/test/regress/sql/select_parallel.sql
+++ b/src/test/regress/sql/select_parallel.sql
@@ -2,6 +2,13 @@
 -- PARALLEL
 --
 
+-- Save parallel worker stats, used for comparison at the end
+select pg_stat_force_next_flush();
+select parallel_workers_to_launch as parallel_workers_to_launch_before,
+       parallel_workers_launched as parallel_workers_launched_before
+  from pg_stat_database
+  where datname = current_database() \gset
+
 create function sp_parallel_restricted(int) returns int as
   $$begin return $1; end$$ language plpgsql parallel restricted;
 
@@ -574,3 +581,10 @@ SET debug_parallel_query = on;
 DELETE FROM parallel_hang WHERE 380 <= i AND i <= 420;
 
 ROLLBACK;
+
+-- Check parallel worker stats
+select pg_stat_force_next_flush();
+select parallel_workers_to_launch > :'parallel_workers_to_launch_before'  AS wrk_to_launch,
+       parallel_workers_launched > :'parallel_workers_launched_before' AS wrk_launched
+  from pg_stat_database
+  where datname = current_database();
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 331315f8d3..840d7f8161 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3611,6 +3611,24 @@ description | Waiting for a newly initialized WAL file to reach durable storage
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_workers_to_launch</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers planned to be launched by queries on this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>parallel_workers_launched</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of parallel workers launched by queries on this database
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
-- 
2.45.2