Add a new GUC and a reloption to enable inserts in parallel-mode.

Commit 05c8482f7f added the implementation of parallel SELECT for
"INSERT INTO ... SELECT ..." which may incur non-negligible overhead in
the additional parallel-safety checks that it performs, even when, in the
end, those checks determine that parallelism can't be used. This is
normally only ever a problem in the case of when the target table has a
large number of partitions.

A new GUC option "enable_parallel_insert" is added, to allow insert in
parallel-mode. The default is on.

In addition to the GUC option, the user may want a mechanism to allow
inserts in parallel-mode with finer granularity at table level. The new
table option "parallel_insert_enabled" allows this. The default is true.

Author: "Hou, Zhijie"
Reviewed-by: Greg Nancarrow, Amit Langote, Takayuki Tsunakawa, Amit Kapila
Discussion: https://postgr.es/m/CAA4eK1K-cW7svLC2D7DHoGHxdAdg3P37BLgebqBOC2ZLc9a6QQ%40mail.gmail.com
Discussion: https://postgr.es/m/CAJcOf-cXnB5cnMKqWEp2E2z7Mvcd04iLVmV=qpFJrR3AcrTS3g@mail.gmail.com

src/backend/access/common/reloptions.c

@@ -168,6 +168,15 @@ static relopt_bool boolRelOpts[] =
 		},
 		true
 	},
+	{
+		{
+			"parallel_insert_enabled",
+			"Enables \"parallel insert\" feature for this table",
+			RELOPT_KIND_HEAP | RELOPT_KIND_PARTITIONED,
+			ShareUpdateExclusiveLock
+		},
+		true
+	},
 	/* list terminator */
 	{{NULL}}
 };
@@ -1859,7 +1868,9 @@ default_reloptions(Datum reloptions, bool validate, relopt_kind kind)
 		{"vacuum_index_cleanup", RELOPT_TYPE_BOOL,
 		offsetof(StdRdOptions, vacuum_index_cleanup)},
 		{"vacuum_truncate", RELOPT_TYPE_BOOL,
-		offsetof(StdRdOptions, vacuum_truncate)}
+		offsetof(StdRdOptions, vacuum_truncate)},
+		{"parallel_insert_enabled", RELOPT_TYPE_BOOL,
+		offsetof(StdRdOptions, parallel_insert_enabled)}
 	};
 
 	return (bytea *) build_reloptions(reloptions, validate, kind,
@@ -1961,13 +1972,15 @@ build_local_reloptions(local_relopts *relopts, Datum options, bool validate)
 bytea *
 partitioned_table_reloptions(Datum reloptions, bool validate)
 {
-	/*
-	 * There are no options for partitioned tables yet, but this is able to do
-	 * some validation.
-	 */
+	static const relopt_parse_elt tab[] = {
+		{"parallel_insert_enabled", RELOPT_TYPE_BOOL,
+		offsetof(PartitionedTableRdOptions, parallel_insert_enabled)}
+	};
+
 	return (bytea *) build_reloptions(reloptions, validate,
 									  RELOPT_KIND_PARTITIONED,
-									  0, NULL, 0);
+									  sizeof(PartitionedTableRdOptions),
+									  tab, lengthof(tab));
 }
 
 /*

src/backend/optimizer/path/costsize.c

@@ -129,6 +129,8 @@ Cost		disable_cost = 1.0e10;
 
 int			max_parallel_workers_per_gather = 2;
 
+bool		enable_parallel_insert = true;
+
 bool		enable_seqscan = true;
 bool		enable_indexscan = true;
 bool		enable_indexonlyscan = true;

src/backend/optimizer/util/clauses.c

@@ -1265,8 +1265,10 @@ target_rel_chk_constr_max_parallel_hazard(Relation rel,
  *
  * It's not possible in the following cases:
  *
- *  1) INSERT...ON CONFLICT...DO UPDATE
- *  2) INSERT without SELECT
+ *  1) enable_parallel_insert is off
+ *  2) INSERT...ON CONFLICT...DO UPDATE
+ *  3) INSERT without SELECT
+ *  4) the reloption parallel_insert_enabled is set to off
  *
  * (Note: we don't do in-depth parallel-safety checks here, we do only the
  * cheaper tests that can quickly exclude obvious cases for which
@@ -1277,12 +1279,17 @@ bool
 is_parallel_allowed_for_modify(Query *parse)
 {
 	bool		hasSubQuery;
+	bool		parallel_enabled;
 	RangeTblEntry *rte;
 	ListCell   *lc;
+	Relation	rel;
 
 	if (!IsModifySupportedInParallelMode(parse->commandType))
 		return false;
 
+	if (!enable_parallel_insert)
+		return false;
+
 	/*
 	 * UPDATE is not currently supported in parallel-mode, so prohibit
 	 * INSERT...ON CONFLICT...DO UPDATE...
@@ -1313,7 +1320,28 @@ is_parallel_allowed_for_modify(Query *parse)
 		}
 	}
 
-	return hasSubQuery;
+	if (!hasSubQuery)
+		return false;
+
+	/*
+	 * Check if parallel_insert_enabled is enabled for the target table, if
+	 * not, skip the safety checks.
+	 *
+	 * (Note: if the target table is partitioned, the parallel_insert_enabled
+	 * option setting of the partitions are ignored).
+	 */
+	rte = rt_fetch(parse->resultRelation, parse->rtable);
+
+	/*
+	 * The target table is already locked by the caller (this is done in the
+	 * parse/analyze phase), and remains locked until end-of-transaction.
+	 */
+	rel = table_open(rte->relid, NoLock);
+
+	parallel_enabled = RelationGetParallelInsert(rel, true);
+	table_close(rel, NoLock);
+
+	return parallel_enabled;
 }
 
 /*****************************************************************************

src/backend/utils/misc/guc.c

@@ -1122,6 +1122,16 @@ static struct config_bool ConfigureNamesBool[] =
 		true,
 		NULL, NULL, NULL
 	},
+	{
+		{"enable_parallel_insert", PGC_USERSET, QUERY_TUNING_METHOD,
+			gettext_noop("Enables the planner's use of parallel plans for INSERT commands."),
+			NULL,
+			GUC_EXPLAIN
+		},
+		&enable_parallel_insert,
+		true,
+		NULL, NULL, NULL
+	},
 	{
 		/* Not for general use --- used by SET SESSION AUTHORIZATION */
 		{"is_superuser", PGC_INTERNAL, UNGROUPED,

src/backend/utils/misc/postgresql.conf.sample

@@ -371,6 +371,7 @@
 #enable_partitionwise_aggregate = off
 #enable_parallel_hash = on
 #enable_partition_pruning = on
+#enable_parallel_insert = on
 
 # - Planner Cost Constants -
 

src/bin/psql/tab-complete.c

@@ -1118,6 +1118,7 @@ static const char *const table_storage_parameters[] = {
 	"autovacuum_vacuum_threshold",
 	"fillfactor",
 	"log_autovacuum_min_duration",
+	"parallel_insert_enabled",
 	"parallel_workers",
 	"toast.autovacuum_enabled",
 	"toast.autovacuum_freeze_max_age",

src/include/optimizer/cost.h

@@ -47,6 +47,7 @@ typedef enum
 /* parameter variables and flags (see also optimizer.h) */
 extern PGDLLIMPORT Cost disable_cost;
 extern PGDLLIMPORT int max_parallel_workers_per_gather;
+extern PGDLLIMPORT bool enable_parallel_insert;
 extern PGDLLIMPORT bool enable_seqscan;
 extern PGDLLIMPORT bool enable_indexscan;
 extern PGDLLIMPORT bool enable_indexonlyscan;

src/include/utils/rel.h

@@ -306,6 +306,8 @@ typedef struct StdRdOptions
 	int			parallel_workers;	/* max number of parallel workers */
 	bool		vacuum_index_cleanup;	/* enables index vacuuming and cleanup */
 	bool		vacuum_truncate;	/* enables vacuum to truncate a relation */
+	bool		parallel_insert_enabled;	/* enables planner's use of
+											 * parallel insert */
 } StdRdOptions;
 
 #define HEAP_MIN_FILLFACTOR			10
@@ -423,6 +425,29 @@ typedef struct ViewOptions
 	 ((ViewOptions *) (relation)->rd_options)->check_option ==				\
 	  VIEW_OPTION_CHECK_OPTION_CASCADED)
 
+/*
+ * PartitionedTableRdOptions
+ *		Contents of rd_options for partitioned tables
+ */
+typedef struct PartitionedTableRdOptions
+{
+	int32		vl_len_;		/* varlena header (do not touch directly!) */
+	bool		parallel_insert_enabled;	/* enables planner's use of
+											 * parallel insert */
+} PartitionedTableRdOptions;
+
+/*
+ * RelationGetParallelInsert
+ *		Returns the relation's parallel_insert_enabled reloption setting.
+ *		Note multiple eval of argument!
+ */
+#define RelationGetParallelInsert(relation, defaultpd) 						\
+	((relation)->rd_options ?												\
+	 (relation->rd_rel->relkind == RELKIND_PARTITIONED_TABLE ?				\
+	 ((PartitionedTableRdOptions *) (relation)->rd_options)->parallel_insert_enabled : \
+	 ((StdRdOptions *) (relation)->rd_options)->parallel_insert_enabled) :		\
+	 (defaultpd))
+
 /*
  * RelationIsValid
  *		True iff relation descriptor is valid.

src/test/regress/expected/insert_parallel.out

@@ -61,12 +61,45 @@ set max_parallel_workers_per_gather=4;
 create table para_insert_p1 (
 	unique1		int4	PRIMARY KEY,
 	stringu1	name
-);
+) with (parallel_insert_enabled = off);
 create table para_insert_f1 (
 	unique1		int4	REFERENCES para_insert_p1(unique1),
 	stringu1	name
 );
 --
+-- Disable guc option enable_parallel_insert
+--
+set enable_parallel_insert = off;
+-- Test INSERT with underlying query when enable_parallel_insert=off and reloption.parallel_insert_enabled=off.
+-- (should create plan with serial INSERT + SELECT)
+--
+explain(costs off) insert into para_insert_p1 select unique1, stringu1 from tenk1;
+        QUERY PLAN        
+--------------------------
+ Insert on para_insert_p1
+   ->  Seq Scan on tenk1
+(2 rows)
+
+--
+-- Reset guc option enable_parallel_insert
+--
+reset enable_parallel_insert;
+--
+-- Test INSERT with underlying query when enable_parallel_insert=on and reloption.parallel_insert_enabled=off.
+-- (should create plan with serial INSERT + SELECT)
+--
+explain(costs off) insert into para_insert_p1 select unique1, stringu1 from tenk1;
+        QUERY PLAN        
+--------------------------
+ Insert on para_insert_p1
+   ->  Seq Scan on tenk1
+(2 rows)
+
+--
+-- Enable reloption parallel_insert_enabled
+--
+alter table para_insert_p1 set (parallel_insert_enabled = on);
+--
 -- Test INSERT with underlying query.
 -- (should create plan with parallel SELECT, Gather parent node)
 --
@@ -362,9 +395,28 @@ explain (costs off) insert into testdef(a,d) select a,a*8 from test_data;
 --
 -- Test INSERT into partition with underlying query.
 --
-create table parttable1 (a int, b name) partition by range (a);
+create table parttable1 (a int, b name) partition by range (a) with (parallel_insert_enabled=off);
 create table parttable1_1 partition of parttable1 for values from (0) to (5000);
 create table parttable1_2 partition of parttable1 for values from (5000) to (10000);
+--
+-- Test INSERT into partition when reloption.parallel_insert_enabled=off
+-- (should not create a parallel plan)
+--
+explain (costs off) insert into parttable1 select unique1,stringu1 from tenk1;
+       QUERY PLAN        
+-------------------------
+ Insert on parttable1
+   ->  Seq Scan on tenk1
+(2 rows)
+
+--
+-- Enable reloption parallel_insert_enabled
+--
+alter table parttable1 set (parallel_insert_enabled = on);
+--
+-- Test INSERT into partition when reloption.parallel_insert_enabled=on
+-- (should create a parallel plan)
+--
 explain (costs off) insert into parttable1 select unique1,stringu1 from tenk1;
                QUERY PLAN               
 ----------------------------------------

src/test/regress/expected/sysviews.out

@@ -107,13 +107,14 @@ select name, setting from pg_settings where name like 'enable%';
  enable_nestloop                | on
  enable_parallel_append         | on
  enable_parallel_hash           | on
+ enable_parallel_insert         | on
  enable_partition_pruning       | on
  enable_partitionwise_aggregate | off
  enable_partitionwise_join      | off
  enable_seqscan                 | on
  enable_sort                    | on
  enable_tidscan                 | on
-(18 rows)
+(19 rows)
 
 -- Test that the pg_timezone_names and pg_timezone_abbrevs views are
 -- more-or-less working.  We can't test their contents in any great detail

src/test/regress/sql/insert_parallel.sql

@@ -77,13 +77,38 @@ set max_parallel_workers_per_gather=4;
 create table para_insert_p1 (
 	unique1		int4	PRIMARY KEY,
 	stringu1	name
-);
+) with (parallel_insert_enabled = off);
 
 create table para_insert_f1 (
 	unique1		int4	REFERENCES para_insert_p1(unique1),
 	stringu1	name
 );
 
+--
+-- Disable guc option enable_parallel_insert
+--
+set enable_parallel_insert = off;
+
+-- Test INSERT with underlying query when enable_parallel_insert=off and reloption.parallel_insert_enabled=off.
+-- (should create plan with serial INSERT + SELECT)
+--
+explain(costs off) insert into para_insert_p1 select unique1, stringu1 from tenk1;
+
+--
+-- Reset guc option enable_parallel_insert
+--
+reset enable_parallel_insert;
+
+--
+-- Test INSERT with underlying query when enable_parallel_insert=on and reloption.parallel_insert_enabled=off.
+-- (should create plan with serial INSERT + SELECT)
+--
+explain(costs off) insert into para_insert_p1 select unique1, stringu1 from tenk1;
+
+--
+-- Enable reloption parallel_insert_enabled
+--
+alter table para_insert_p1 set (parallel_insert_enabled = on);
 
 --
 -- Test INSERT with underlying query.
@@ -208,10 +233,25 @@ explain (costs off) insert into testdef(a,d) select a,a*8 from test_data;
 --
 -- Test INSERT into partition with underlying query.
 --
-create table parttable1 (a int, b name) partition by range (a);
+create table parttable1 (a int, b name) partition by range (a) with (parallel_insert_enabled=off);
 create table parttable1_1 partition of parttable1 for values from (0) to (5000);
 create table parttable1_2 partition of parttable1 for values from (5000) to (10000);
 
+--
+-- Test INSERT into partition when reloption.parallel_insert_enabled=off
+-- (should not create a parallel plan)
+--
+explain (costs off) insert into parttable1 select unique1,stringu1 from tenk1;
+
+--
+-- Enable reloption parallel_insert_enabled
+--
+alter table parttable1 set (parallel_insert_enabled = on);
+
+--
+-- Test INSERT into partition when reloption.parallel_insert_enabled=on
+-- (should create a parallel plan)
+--
 explain (costs off) insert into parttable1 select unique1,stringu1 from tenk1;
 insert into parttable1 select unique1,stringu1 from tenk1;
 select count(*) from parttable1_1;

src/tools/pgindent/typedefs.list

@@ -1797,6 +1797,7 @@ PartitionSpec
 PartitionTupleRouting
 PartitionedRelPruneInfo
 PartitionedRelPruningData
+PartitionedTableRdOptions
 PartitionwiseAggregateType
 PasswordType
 Path