Enable parallel SELECT for "INSERT INTO ... SELECT ...".

Parallel SELECT can't be utilized for INSERT in the following cases:
- INSERT statement uses the ON CONFLICT DO UPDATE clause
- Target table has a parallel-unsafe: trigger, index expression or
  predicate, column default expression or check constraint
- Target table has a parallel-unsafe domain constraint on any column
- Target table is a partitioned table with a parallel-unsafe partition key
  expression or support function

The planner is updated to perform additional parallel-safety checks for
the cases listed above, for determining whether it is safe to run INSERT
in parallel-mode with an underlying parallel SELECT. The planner will
consider using parallel SELECT for "INSERT INTO ... SELECT ...", provided
nothing unsafe is found from the additional parallel-safety checks, or
from the existing parallel-safety checks for SELECT.

While checking parallel-safety, we need to check it for all the partitions
on the table which can be costly especially when we decide not to use a
parallel plan. So, in a separate patch, we will introduce a GUC and or a
reloption to enable/disable parallelism for Insert statements.

Prior to entering parallel-mode for the execution of INSERT with parallel
SELECT, a TransactionId is acquired and assigned to the current
transaction state. This is necessary to prevent the INSERT from attempting
to assign the TransactionId whilst in parallel-mode, which is not allowed.
This approach has a disadvantage in that if the underlying SELECT does not
return any rows, then the TransactionId is not used, however that
shouldn't happen in practice in many cases.

Author: Greg Nancarrow, Amit Langote, Amit Kapila
Reviewed-by: Amit Langote, Hou Zhijie, Takayuki Tsunakawa, Antonin Houska, Bharath Rupireddy, Dilip Kumar, Vignesh C, Zhihong Yu, Amit Kapila
Tested-by: Tang, Haiying
Discussion: https://postgr.es/m/CAJcOf-cXnB5cnMKqWEp2E2z7Mvcd04iLVmV=qpFJrR3AcrTS3g@mail.gmail.com
Discussion: https://postgr.es/m/CAJcOf-fAdj=nDKMsRhQzndm-O13NY4dL6xGcEvdX5Xvbbi0V7g@mail.gmail.com

doc/src/sgml/parallel.sgml

@@ -146,7 +146,9 @@ EXPLAIN SELECT * FROM pgbench_accounts WHERE filler LIKE '%x%';
         a CTE, no parallel plans for that query will be generated.  As an
         exception, the commands <literal>CREATE TABLE ... AS</literal>, <literal>SELECT
         INTO</literal>, and <literal>CREATE MATERIALIZED VIEW</literal> which create a new
-        table and populate it can use a parallel plan.
+        table and populate it can use a parallel plan. Another exception is the command
+        <literal>INSERT INTO ... SELECT ...</literal> which can use a parallel plan for
+        the underlying <literal>SELECT</literal> part of the query.
       </para>
     </listitem>
 

src/backend/access/transam/xact.c

@@ -1014,6 +1014,32 @@ IsInParallelMode(void)
 	return CurrentTransactionState->parallelModeLevel != 0;
 }
 
+/*
+ *	PrepareParallelModePlanExec
+ *
+ * Prepare for entering parallel mode plan execution, based on command-type.
+ */
+void
+PrepareParallelModePlanExec(CmdType commandType)
+{
+	if (IsModifySupportedInParallelMode(commandType))
+	{
+		Assert(!IsInParallelMode());
+
+		/*
+		 * Prepare for entering parallel mode by assigning a TransactionId.
+		 * Failure to do this now would result in heap_insert() subsequently
+		 * attempting to assign a TransactionId whilst in parallel-mode, which
+		 * is not allowed.
+		 *
+		 * This approach has a disadvantage in that if the underlying SELECT
+		 * does not return any rows, then the TransactionId is not used,
+		 * however that shouldn't happen in practice in many cases.
+		 */
+		(void) GetCurrentTransactionId();
+	}
+}
+
 /*
  *	CommandCounterIncrement
  */

src/backend/executor/execMain.c

@@ -1512,7 +1512,10 @@ ExecutePlan(EState *estate,
 
 	estate->es_use_parallel_mode = use_parallel_mode;
 	if (use_parallel_mode)
+	{
+		PrepareParallelModePlanExec(estate->es_plannedstmt->commandType);
 		EnterParallelMode();
+	}
 
 	/*
 	 * Loop until we've processed the proper number of tuples from the plan.

src/backend/nodes/copyfuncs.c

@@ -96,6 +96,7 @@ _copyPlannedStmt(const PlannedStmt *from)
 	COPY_BITMAPSET_FIELD(rewindPlanIDs);
 	COPY_NODE_FIELD(rowMarks);
 	COPY_NODE_FIELD(relationOids);
+	COPY_NODE_FIELD(partitionOids);
 	COPY_NODE_FIELD(invalItems);
 	COPY_NODE_FIELD(paramExecTypes);
 	COPY_NODE_FIELD(utilityStmt);

src/backend/nodes/outfuncs.c

@@ -314,6 +314,7 @@ _outPlannedStmt(StringInfo str, const PlannedStmt *node)
 	WRITE_BITMAPSET_FIELD(rewindPlanIDs);
 	WRITE_NODE_FIELD(rowMarks);
 	WRITE_NODE_FIELD(relationOids);
+	WRITE_NODE_FIELD(partitionOids);
 	WRITE_NODE_FIELD(invalItems);
 	WRITE_NODE_FIELD(paramExecTypes);
 	WRITE_NODE_FIELD(utilityStmt);
@@ -2221,6 +2222,7 @@ _outPlannerGlobal(StringInfo str, const PlannerGlobal *node)
 	WRITE_NODE_FIELD(resultRelations);
 	WRITE_NODE_FIELD(appendRelations);
 	WRITE_NODE_FIELD(relationOids);
+	WRITE_NODE_FIELD(partitionOids);
 	WRITE_NODE_FIELD(invalItems);
 	WRITE_NODE_FIELD(paramExecTypes);
 	WRITE_UINT_FIELD(lastPHId);

src/backend/nodes/readfuncs.c

@@ -1590,6 +1590,7 @@ _readPlannedStmt(void)
 	READ_BITMAPSET_FIELD(rewindPlanIDs);
 	READ_NODE_FIELD(rowMarks);
 	READ_NODE_FIELD(relationOids);
+	READ_NODE_FIELD(partitionOids);
 	READ_NODE_FIELD(invalItems);
 	READ_NODE_FIELD(paramExecTypes);
 	READ_NODE_FIELD(utilityStmt);

src/backend/optimizer/plan/planner.c

@@ -305,6 +305,7 @@ standard_planner(Query *parse, const char *query_string, int cursorOptions,
 	glob->resultRelations = NIL;
 	glob->appendRelations = NIL;
 	glob->relationOids = NIL;
+	glob->partitionOids = NIL;
 	glob->invalItems = NIL;
 	glob->paramExecTypes = NIL;
 	glob->lastPHId = 0;
@@ -316,16 +317,16 @@ standard_planner(Query *parse, const char *query_string, int cursorOptions,
 	/*
 	 * Assess whether it's feasible to use parallel mode for this query. We
 	 * can't do this in a standalone backend, or if the command will try to
-	 * modify any data, or if this is a cursor operation, or if GUCs are set
+	 * modify any data (except for Insert), or if this is a cursor operation,
-	 * to values that don't permit parallelism, or if parallel-unsafe
+	 * or if GUCs are set to values that don't permit parallelism, or if
-	 * functions are present in the query tree.
+	 * parallel-unsafe functions are present in the query tree.
 	 *
-	 * (Note that we do allow CREATE TABLE AS, SELECT INTO, and CREATE
+	 * (Note that we do allow CREATE TABLE AS, INSERT INTO...SELECT, SELECT
-	 * MATERIALIZED VIEW to use parallel plans, but as of now, only the leader
+	 * INTO, and CREATE MATERIALIZED VIEW to use parallel plans. However, as
-	 * backend writes into a completely new table.  In the future, we can
+	 * of now, only the leader backend writes into a completely new table. In
-	 * extend it to allow workers to write into the table.  However, to allow
+	 * the future, we can extend it to allow workers to write into the table.
-	 * parallel updates and deletes, we have to solve other problems,
+	 * However, to allow parallel updates and deletes, we have to solve other
-	 * especially around combo CIDs.)
+	 * problems, especially around combo CIDs.)
 	 *
 	 * For now, we don't try to use parallel mode if we're running inside a
 	 * parallel worker.  We might eventually be able to relax this
@@ -334,13 +335,14 @@ standard_planner(Query *parse, const char *query_string, int cursorOptions,
 	 */
 	if ((cursorOptions & CURSOR_OPT_PARALLEL_OK) != 0 &&
 		IsUnderPostmaster &&
-		parse->commandType == CMD_SELECT &&
+		(parse->commandType == CMD_SELECT ||
+		 is_parallel_allowed_for_modify(parse)) &&
 		!parse->hasModifyingCTE &&
 		max_parallel_workers_per_gather > 0 &&
 		!IsParallelWorker())
 	{
 		/* all the cheap tests pass, so scan the query tree */
-		glob->maxParallelHazard = max_parallel_hazard(parse);
+		glob->maxParallelHazard = max_parallel_hazard(parse, glob);
 		glob->parallelModeOK = (glob->maxParallelHazard != PROPARALLEL_UNSAFE);
 	}
 	else
@@ -521,6 +523,19 @@ standard_planner(Query *parse, const char *query_string, int cursorOptions,
 	result->rewindPlanIDs = glob->rewindPlanIDs;
 	result->rowMarks = glob->finalrowmarks;
 	result->relationOids = glob->relationOids;
+
+	/*
+	 * Register the Oids of parallel-safety-checked partitions as plan
+	 * dependencies. This is only really needed in the case of a parallel plan
+	 * so that if parallel-unsafe properties are subsequently defined on the
+	 * partitions, the cached parallel plan will be invalidated, and a
+	 * non-parallel plan will be generated.
+	 *
+	 * We also use this list to acquire locks on partitions before executing
+	 * cached plan. See AcquireExecutorLocks().
+	 */
+	if (glob->partitionOids != NIL && glob->parallelModeNeeded)
+		result->partitionOids = glob->partitionOids;
 	result->invalItems = glob->invalItems;
 	result->paramExecTypes = glob->paramExecTypes;
 	/* utilityStmt should be null, but we might as well copy it */

src/backend/optimizer/util/clauses.c

@@ -19,13 +19,18 @@
 
 #include "postgres.h"
 
+#include "access/genam.h"
 #include "access/htup_details.h"
+#include "access/table.h"
+#include "access/xact.h"
 #include "catalog/pg_aggregate.h"
 #include "catalog/pg_class.h"
+#include "catalog/pg_constraint.h"
 #include "catalog/pg_language.h"
 #include "catalog/pg_operator.h"
 #include "catalog/pg_proc.h"
 #include "catalog/pg_type.h"
+#include "commands/trigger.h"
 #include "executor/executor.h"
 #include "executor/functions.h"
 #include "funcapi.h"
@@ -43,6 +48,8 @@
 #include "parser/parse_agg.h"
 #include "parser/parse_coerce.h"
 #include "parser/parse_func.h"
+#include "parser/parsetree.h"
+#include "partitioning/partdesc.h"
 #include "rewrite/rewriteManip.h"
 #include "tcop/tcopprot.h"
 #include "utils/acl.h"
@@ -51,6 +58,8 @@
 #include "utils/fmgroids.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
+#include "utils/partcache.h"
+#include "utils/rel.h"
 #include "utils/syscache.h"
 #include "utils/typcache.h"
 
@@ -88,6 +97,9 @@ typedef struct
 	char		max_hazard;		/* worst proparallel hazard found so far */
 	char		max_interesting;	/* worst proparallel hazard of interest */
 	List	   *safe_param_ids; /* PARAM_EXEC Param IDs to treat as safe */
+	RangeTblEntry *target_rte;	/* query's target relation if any */
+	CmdType		command_type;	/* query's command type */
+	PlannerGlobal *planner_global;	/* global info for planner invocation */
 } max_parallel_hazard_context;
 
 static bool contain_agg_clause_walker(Node *node, void *context);
@@ -98,6 +110,20 @@ static bool contain_volatile_functions_walker(Node *node, void *context);
 static bool contain_volatile_functions_not_nextval_walker(Node *node, void *context);
 static bool max_parallel_hazard_walker(Node *node,
 									   max_parallel_hazard_context *context);
+static bool target_rel_max_parallel_hazard(max_parallel_hazard_context *context);
+static bool target_rel_max_parallel_hazard_recurse(Relation relation,
+												   CmdType command_type,
+												   max_parallel_hazard_context *context);
+static bool target_rel_trigger_max_parallel_hazard(TriggerDesc *trigdesc,
+												   max_parallel_hazard_context *context);
+static bool target_rel_index_max_parallel_hazard(Relation rel,
+												 max_parallel_hazard_context *context);
+static bool target_rel_domain_max_parallel_hazard(Oid typid,
+												  max_parallel_hazard_context *context);
+static bool target_rel_partitions_max_parallel_hazard(Relation rel,
+													  max_parallel_hazard_context *context);
+static bool target_rel_chk_constr_max_parallel_hazard(Relation rel,
+													  max_parallel_hazard_context *context);
 static bool contain_nonstrict_functions_walker(Node *node, void *context);
 static bool contain_exec_param_walker(Node *node, List *param_ids);
 static bool contain_context_dependent_node(Node *clause);
@@ -545,14 +571,19 @@ contain_volatile_functions_not_nextval_walker(Node *node, void *context)
  * later, in the common case where everything is SAFE.
  */
 char
-max_parallel_hazard(Query *parse)
+max_parallel_hazard(Query *parse, PlannerGlobal *glob)
 {
 	max_parallel_hazard_context context;
 
 	context.max_hazard = PROPARALLEL_SAFE;
 	context.max_interesting = PROPARALLEL_UNSAFE;
 	context.safe_param_ids = NIL;
+	context.target_rte = parse->resultRelation > 0 ?
+		rt_fetch(parse->resultRelation, parse->rtable) : NULL;
+	context.command_type = parse->commandType;
+	context.planner_global = glob;
 	(void) max_parallel_hazard_walker((Node *) parse, &context);
+
 	return context.max_hazard;
 }
 
@@ -583,6 +614,9 @@ is_parallel_safe(PlannerInfo *root, Node *node)
 	context.max_hazard = PROPARALLEL_SAFE;
 	context.max_interesting = PROPARALLEL_RESTRICTED;
 	context.safe_param_ids = NIL;
+	context.command_type = node != NULL && IsA(node, Query) ?
+		castNode(Query, node)->commandType : CMD_UNKNOWN;
+	context.planner_global = root->glob;
 
 	/*
 	 * The params that refer to the same or parent query level are considered
@@ -655,14 +689,20 @@ max_parallel_hazard_walker(Node *node, max_parallel_hazard_context *context)
 	 * opclass support functions are generally parallel-safe.  XmlExpr is a
 	 * bit more dubious but we can probably get away with it.  We err on the
 	 * side of caution by treating CoerceToDomain as parallel-restricted.
-	 * (Note: in principle that's wrong because a domain constraint could
+	 * However, for table modification statements, we check the parallel
-	 * contain a parallel-unsafe function; but useful constraints probably
+	 * safety of domain constraints as that could contain a parallel-unsafe
-	 * never would have such, and assuming they do would cripple use of
+	 * function, and executing that in parallel mode will lead to error.
-	 * parallel query in the presence of domain types.)  SQLValueFunction
+	 * SQLValueFunction should be safe in all cases.  NextValueExpr is
-	 * should be safe in all cases.  NextValueExpr is parallel-unsafe.
+	 * parallel-unsafe.
 	 */
 	if (IsA(node, CoerceToDomain))
 	{
+		if (context->target_rte != NULL)
+		{
+			if (target_rel_domain_max_parallel_hazard(((CoerceToDomain *) node)->resulttype, context))
+				return true;
+		}
+
 		if (max_parallel_hazard_test(PROPARALLEL_RESTRICTED, context))
 			return true;
 	}
@@ -687,6 +727,27 @@ max_parallel_hazard_walker(Node *node, max_parallel_hazard_context *context)
 			return true;
 	}
 
+	/*
+	 * ModifyingCTE expressions are treated as parallel-unsafe.
+	 *
+	 * XXX Normally, if the Query has a modifying CTE, the hasModifyingCTE
+	 * flag is set in the Query tree, and the query will be regarded as
+	 * parallel-usafe. However, in some cases, a re-written query with a
+	 * modifying CTE does not have that flag set, due to a bug in the query
+	 * rewriter.
+	 */
+	else if (IsA(node, CommonTableExpr))
+	{
+		CommonTableExpr *cte = (CommonTableExpr *) node;
+		Query	   *ctequery = castNode(Query, cte->ctequery);
+
+		if (ctequery->commandType != CMD_SELECT)
+		{
+			context->max_hazard = PROPARALLEL_UNSAFE;
+			return true;
+		}
+	}
+
 	/*
 	 * As a notational convenience for callers, look through RestrictInfo.
 	 */
@@ -757,6 +818,19 @@ max_parallel_hazard_walker(Node *node, max_parallel_hazard_context *context)
 		}
 		return false;			/* nothing to recurse to */
 	}
+	else if (IsA(node, RangeTblEntry))
+	{
+		RangeTblEntry *rte = (RangeTblEntry *) node;
+
+		/* Nothing interesting to check for SELECTs */
+		if (context->target_rte == NULL)
+			return false;
+
+		if (rte == context->target_rte)
+			return target_rel_max_parallel_hazard(context);
+
+		return false;
+	}
 
 	/*
 	 * When we're first invoked on a completely unplanned tree, we must
@@ -777,7 +851,9 @@ max_parallel_hazard_walker(Node *node, max_parallel_hazard_context *context)
 		/* Recurse into subselects */
 		return query_tree_walker(query,
 								 max_parallel_hazard_walker,
-								 context, 0);
+								 context,
+								 context->target_rte != NULL ?
+								 QTW_EXAMINE_RTES_BEFORE : 0);
 	}
 
 	/* Recurse to check arguments */
@@ -786,6 +862,466 @@ max_parallel_hazard_walker(Node *node, max_parallel_hazard_context *context)
 								  context);
 }
 
+/*
+ * target_rel_max_parallel_hazard
+ *
+ * Determines the maximum parallel-mode hazard level for modification
+ * of a specified relation.
+ */
+static bool
+target_rel_max_parallel_hazard(max_parallel_hazard_context *context)
+{
+	bool		max_hazard_found;
+
+	Relation	targetRel;
+
+	/*
+	 * The target table is already locked by the caller (this is done in the
+	 * parse/analyze phase), and remains locked until end-of-transaction.
+	 */
+	targetRel = table_open(context->target_rte->relid, NoLock);
+	max_hazard_found = target_rel_max_parallel_hazard_recurse(targetRel,
+															  context->command_type,
+															  context);
+	table_close(targetRel, NoLock);
+
+	return max_hazard_found;
+}
+
+static bool
+target_rel_max_parallel_hazard_recurse(Relation rel,
+									   CmdType command_type,
+									   max_parallel_hazard_context *context)
+{
+	/* Currently only CMD_INSERT is supported */
+	Assert(command_type == CMD_INSERT);
+
+	/*
+	 * We can't support table modification in a parallel worker if it's a
+	 * foreign table/partition (no FDW API for supporting parallel access) or
+	 * a temporary table.
+	 */
+	if (rel->rd_rel->relkind == RELKIND_FOREIGN_TABLE ||
+		RelationUsesLocalBuffers(rel))
+	{
+		if (max_parallel_hazard_test(PROPARALLEL_RESTRICTED, context))
+			return true;
+	}
+
+	/*
+	 * If a partitioned table, check that each partition is safe for
+	 * modification in parallel-mode.
+	 */
+	if (target_rel_partitions_max_parallel_hazard(rel, context))
+		return true;
+
+	/*
+	 * If there are any index expressions or index predicate, check that they
+	 * are parallel-mode safe.
+	 */
+	if (target_rel_index_max_parallel_hazard(rel, context))
+		return true;
+
+	/*
+	 * If any triggers exist, check that they are parallel-safe.
+	 */
+	if (target_rel_trigger_max_parallel_hazard(rel->trigdesc, context))
+		return true;
+
+	/*
+	 * Column default expressions are only applicable to INSERT and UPDATE.
+	 * For columns in the target-list, these are already being checked for
+	 * parallel-safety in the max_parallel_hazard() scan of the query tree in
+	 * standard_planner(), so there's no need to do it here. Note that even
+	 * though column defaults may be specified separately for each partition
+	 * in a partitioned table, a partition's default value is not applied when
+	 * inserting a tuple through a partitioned table.
+	 */
+
+	/*
+	 * CHECK constraints are only applicable to INSERT and UPDATE. If any
+	 * CHECK constraints exist, determine if they are parallel-safe.
+	 */
+	if (target_rel_chk_constr_max_parallel_hazard(rel, context))
+		return true;
+
+	return false;
+}
+
+/*
+ * target_rel_trigger_max_parallel_hazard
+ *
+ * Finds the maximum parallel-mode hazard level for the specified trigger data.
+ */
+static bool
+target_rel_trigger_max_parallel_hazard(TriggerDesc *trigdesc,
+									   max_parallel_hazard_context *context)
+{
+	int			i;
+
+	if (trigdesc == NULL)
+		return false;
+
+	for (i = 0; i < trigdesc->numtriggers; i++)
+	{
+		int			trigtype;
+		Trigger    *trigger = &trigdesc->triggers[i];
+
+		if (max_parallel_hazard_test(func_parallel(trigger->tgfoid), context))
+			return true;
+
+		/*
+		 * If the trigger type is RI_TRIGGER_FK, this indicates a FK exists in
+		 * the relation, and this would result in creation of new CommandIds
+		 * on insert/update and this isn't supported in a parallel worker (but
+		 * is safe in the parallel leader).
+		 */
+		trigtype = RI_FKey_trigger_type(trigger->tgfoid);
+		if (trigtype == RI_TRIGGER_FK)
+		{
+			if (max_parallel_hazard_test(PROPARALLEL_RESTRICTED, context))
+				return true;
+		}
+	}
+
+	return false;
+}
+
+/*
+ * target_rel_index_max_parallel_hazard
+ *
+ * Finds the maximum parallel-mode hazard level for any existing index
+ * expressions or index predicate of a specified relation.
+ */
+static bool
+target_rel_index_max_parallel_hazard(Relation rel,
+									 max_parallel_hazard_context *context)
+{
+	List	   *index_oid_list;
+	ListCell   *lc;
+	bool		found_max_hazard = false;
+	LOCKMODE	lockmode = AccessShareLock;
+
+	index_oid_list = RelationGetIndexList(rel);
+	foreach(lc, index_oid_list)
+	{
+		Relation	index_rel;
+		Form_pg_index indexStruct;
+		List	   *ii_Expressions;
+		List	   *ii_Predicate;
+		Oid			index_oid = lfirst_oid(lc);
+
+		index_rel = index_open(index_oid, lockmode);
+
+		indexStruct = index_rel->rd_index;
+		ii_Expressions = RelationGetIndexExpressions(index_rel);
+
+		if (ii_Expressions != NIL)
+		{
+			int			i;
+			ListCell   *index_expr_item = list_head(ii_Expressions);
+
+			for (i = 0; i < indexStruct->indnatts; i++)
+			{
+				int			keycol = indexStruct->indkey.values[i];
+
+				if (keycol == 0)
+				{
+					/* Found an index expression */
+
+					Node	   *index_expr;
+
+					Assert(index_expr_item != NULL);
+					if (index_expr_item == NULL)	/* shouldn't happen */
+					{
+						elog(WARNING, "too few entries in indexprs list");
+						context->max_hazard = PROPARALLEL_UNSAFE;
+						found_max_hazard = true;
+						break;
+					}
+
+					index_expr = (Node *) lfirst(index_expr_item);
+
+					if (max_parallel_hazard_walker(index_expr, context))
+					{
+						found_max_hazard = true;
+						break;
+					}
+
+					index_expr_item = lnext(ii_Expressions, index_expr_item);
+				}
+			}
+		}
+
+		if (!found_max_hazard)
+		{
+			ii_Predicate = RelationGetIndexPredicate(index_rel);
+			if (ii_Predicate != NIL)
+			{
+				if (max_parallel_hazard_walker((Node *) ii_Predicate, context))
+					found_max_hazard = true;
+			}
+		}
+
+		/*
+		 * XXX We don't need to retain lock on index as index expressions
+		 * can't be changed later.
+		 */
+		index_close(index_rel, lockmode);
+	}
+	list_free(index_oid_list);
+
+	return found_max_hazard;
+}
+
+/*
+ * target_rel_domain_max_parallel_hazard
+ *
+ * Finds the maximum parallel-mode hazard level for the specified DOMAIN type.
+ * Only any CHECK expressions are examined for parallel-safety.
+ */
+static bool
+target_rel_domain_max_parallel_hazard(Oid typid, max_parallel_hazard_context *context)
+{
+	Relation	con_rel;
+	ScanKeyData key[1];
+	SysScanDesc scan;
+	HeapTuple	tup;
+	bool		found_max_hazard = false;
+
+	LOCKMODE	lockmode = AccessShareLock;
+
+	con_rel = table_open(ConstraintRelationId, lockmode);
+
+	ScanKeyInit(&key[0],
+				Anum_pg_constraint_contypid, BTEqualStrategyNumber,
+				F_OIDEQ, ObjectIdGetDatum(typid));
+	scan = systable_beginscan(con_rel, ConstraintTypidIndexId, true,
+							  NULL, 1, key);
+
+	while (HeapTupleIsValid((tup = systable_getnext(scan))))
+	{
+		Form_pg_constraint con = (Form_pg_constraint) GETSTRUCT(tup);
+
+		if (con->contype == CONSTRAINT_CHECK)
+		{
+			char	   *conbin;
+			Datum		val;
+			bool		isnull;
+			Expr	   *check_expr;
+
+			val = SysCacheGetAttr(CONSTROID, tup,
+								  Anum_pg_constraint_conbin, &isnull);
+			Assert(!isnull);
+			if (isnull)
+			{
+				/*
+				 * This shouldn't ever happen, but if it does, log a WARNING
+				 * and return UNSAFE, rather than erroring out.
+				 */
+				elog(WARNING, "null conbin for constraint %u", con->oid);
+				context->max_hazard = PROPARALLEL_UNSAFE;
+				found_max_hazard = true;
+				break;
+			}
+			conbin = TextDatumGetCString(val);
+			check_expr = stringToNode(conbin);
+			pfree(conbin);
+			if (max_parallel_hazard_walker((Node *) check_expr, context))
+			{
+				found_max_hazard = true;
+				break;
+			}
+		}
+	}
+
+	systable_endscan(scan);
+	table_close(con_rel, lockmode);
+	return found_max_hazard;
+}
+
+/*
+ * target_rel_partitions_max_parallel_hazard
+ *
+ * Finds the maximum parallel-mode hazard level for any partitions of a
+ * of a specified relation.
+ */
+static bool
+target_rel_partitions_max_parallel_hazard(Relation rel,
+										  max_parallel_hazard_context *context)
+{
+	int			i;
+	PartitionDesc pdesc;
+	PartitionKey pkey;
+	ListCell   *partexprs_item;
+	int			partnatts;
+	List	   *partexprs;
+	PlannerGlobal *glob;
+
+
+	if (rel->rd_rel->relkind != RELKIND_PARTITIONED_TABLE)
+		return false;
+
+	pkey = RelationGetPartitionKey(rel);
+
+	partnatts = get_partition_natts(pkey);
+	partexprs = get_partition_exprs(pkey);
+
+	partexprs_item = list_head(partexprs);
+	for (i = 0; i < partnatts; i++)
+	{
+		/* Check parallel-safety of partition key support functions */
+		if (OidIsValid(pkey->partsupfunc[i].fn_oid))
+		{
+			if (max_parallel_hazard_test(func_parallel(pkey->partsupfunc[i].fn_oid), context))
+				return true;
+		}
+
+		/* Check parallel-safety of any expressions in the partition key */
+		if (get_partition_col_attnum(pkey, i) == 0)
+		{
+			Node	   *check_expr = (Node *) lfirst(partexprs_item);
+
+			if (max_parallel_hazard_walker(check_expr, context))
+				return true;
+
+			partexprs_item = lnext(partexprs, partexprs_item);
+		}
+	}
+
+	/* Recursively check each partition ... */
+
+	/* Create the PartitionDirectory infrastructure if we didn't already */
+	glob = context->planner_global;
+	if (glob->partition_directory == NULL)
+		glob->partition_directory =
+			CreatePartitionDirectory(CurrentMemoryContext);
+
+	pdesc = PartitionDirectoryLookup(glob->partition_directory, rel);
+
+	for (i = 0; i < pdesc->nparts; i++)
+	{
+		bool		max_hazard_found;
+		Relation	part_rel;
+
+		/*
+		 * The partition needs to be locked, and remain locked until
+		 * end-of-transaction to ensure its parallel-safety state is not
+		 * hereafter altered.
+		 */
+		part_rel = table_open(pdesc->oids[i], context->target_rte->rellockmode);
+		max_hazard_found = target_rel_max_parallel_hazard_recurse(part_rel,
+																  context->command_type,
+																  context);
+		table_close(part_rel, NoLock);
+
+		/*
+		 * Remember partitionOids to record the partition as a potential plan
+		 * dependency.
+		 */
+		glob->partitionOids = lappend_oid(glob->partitionOids, pdesc->oids[i]);
+
+		if (max_hazard_found)
+			return true;
+	}
+
+	return false;
+}
+
+/*
+ * target_rel_chk_constr_max_parallel_hazard
+ *
+ * Finds the maximum parallel-mode hazard level for any CHECK expressions or
+ * CHECK constraints related to the specified relation.
+ */
+static bool
+target_rel_chk_constr_max_parallel_hazard(Relation rel,
+										  max_parallel_hazard_context *context)
+{
+	TupleDesc	tupdesc;
+
+	tupdesc = RelationGetDescr(rel);
+
+	/*
+	 * Determine if there are any CHECK constraints which are not
+	 * parallel-safe.
+	 */
+	if (tupdesc->constr != NULL && tupdesc->constr->num_check > 0)
+	{
+		int			i;
+
+		ConstrCheck *check = tupdesc->constr->check;
+
+		for (i = 0; i < tupdesc->constr->num_check; i++)
+		{
+			Expr	   *check_expr = stringToNode(check->ccbin);
+
+			if (max_parallel_hazard_walker((Node *) check_expr, context))
+				return true;
+		}
+	}
+
+	return false;
+}
+
+/*
+ * is_parallel_allowed_for_modify
+ *
+ * Check at a high-level if parallel mode is able to be used for the specified
+ * table-modification statement. Currently, we support only Inserts.
+ *
+ * It's not possible in the following cases:
+ *
+ *  1) INSERT...ON CONFLICT...DO UPDATE
+ *  2) INSERT without SELECT
+ *
+ * (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
+ * parallelism isn't supported, to avoid having to do further parallel-safety
+ * checks for these)
+ */
+bool
+is_parallel_allowed_for_modify(Query *parse)
+{
+	bool		hasSubQuery;
+	RangeTblEntry *rte;
+	ListCell   *lc;
+
+	if (!IsModifySupportedInParallelMode(parse->commandType))
+		return false;
+
+	/*
+	 * UPDATE is not currently supported in parallel-mode, so prohibit
+	 * INSERT...ON CONFLICT...DO UPDATE...
+	 *
+	 * In order to support update, even if only in the leader, some further
+	 * work would need to be done. A mechanism would be needed for sharing
+	 * combo-cids between leader and workers during parallel-mode, since for
+	 * example, the leader might generate a combo-cid and it needs to be
+	 * propagated to the workers.
+	 */
+	if (parse->commandType == CMD_INSERT &&
+		parse->onConflict != NULL &&
+		parse->onConflict->action == ONCONFLICT_UPDATE)
+		return false;
+
+	/*
+	 * If there is no underlying SELECT, a parallel insert operation is not
+	 * desirable.
+	 */
+	hasSubQuery = false;
+	foreach(lc, parse->rtable)
+	{
+		rte = lfirst_node(RangeTblEntry, lc);
+		if (rte->rtekind == RTE_SUBQUERY)
+		{
+			hasSubQuery = true;
+			break;
+		}
+	}
+
+	return hasSubQuery;
+}
 
 /*****************************************************************************
  *		Check clauses for nonstrict functions

src/backend/utils/cache/plancache.c

@@ -1735,6 +1735,23 @@ QueryListGetPrimaryStmt(List *stmts)
 	return NULL;
 }
 
+static void
+AcquireExecutorLocksOnPartitions(List *partitionOids, int lockmode,
+								 bool acquire)
+{
+	ListCell   *lc;
+
+	foreach(lc, partitionOids)
+	{
+		Oid			partOid = lfirst_oid(lc);
+
+		if (acquire)
+			LockRelationOid(partOid, lockmode);
+		else
+			UnlockRelationOid(partOid, lockmode);
+	}
+}
+
 /*
  * AcquireExecutorLocks: acquire locks needed for execution of a cached plan;
  * or release them if acquire is false.
@@ -1748,6 +1765,8 @@ AcquireExecutorLocks(List *stmt_list, bool acquire)
 	{
 		PlannedStmt *plannedstmt = lfirst_node(PlannedStmt, lc1);
 		ListCell   *lc2;
+		Index		rti,
+					resultRelation = 0;
 
 		if (plannedstmt->commandType == CMD_UTILITY)
 		{
@@ -1765,6 +1784,9 @@ AcquireExecutorLocks(List *stmt_list, bool acquire)
 			continue;
 		}
 
+		rti = 1;
+		if (plannedstmt->resultRelations)
+			resultRelation = linitial_int(plannedstmt->resultRelations);
 		foreach(lc2, plannedstmt->rtable)
 		{
 			RangeTblEntry *rte = (RangeTblEntry *) lfirst(lc2);
@@ -1782,6 +1804,14 @@ AcquireExecutorLocks(List *stmt_list, bool acquire)
 				LockRelationOid(rte->relid, rte->rellockmode);
 			else
 				UnlockRelationOid(rte->relid, rte->rellockmode);
+
+			/* Lock partitions ahead of modifying them in parallel mode. */
+			if (rti == resultRelation &&
+				plannedstmt->partitionOids != NIL)
+				AcquireExecutorLocksOnPartitions(plannedstmt->partitionOids,
+												 rte->rellockmode, acquire);
+
+			rti++;
 		}
 	}
 }
@@ -1990,7 +2020,8 @@ PlanCacheRelCallback(Datum arg, Oid relid)
 				if (plannedstmt->commandType == CMD_UTILITY)
 					continue;	/* Ignore utility statements */
 				if ((relid == InvalidOid) ? plannedstmt->relationOids != NIL :
-					list_member_oid(plannedstmt->relationOids, relid))
+					(list_member_oid(plannedstmt->relationOids, relid) ||
+					 list_member_oid(plannedstmt->partitionOids, relid)))
 				{
 					/* Invalidate the generic plan only */
 					plansource->gplan->is_valid = false;

src/include/access/xact.h

@@ -466,5 +466,20 @@ extern void ParsePrepareRecord(uint8 info, xl_xact_prepare *xlrec, xl_xact_parse
 extern void EnterParallelMode(void);
 extern void ExitParallelMode(void);
 extern bool IsInParallelMode(void);
+extern void PrepareParallelModePlanExec(CmdType commandType);
+
+/*
+ * IsModifySupportedInParallelMode
+ *
+ * Indicates whether execution of the specified table-modification command
+ * (INSERT/UPDATE/DELETE) in parallel-mode is supported, subject to certain
+ * parallel-safety conditions.
+ */
+static inline bool
+IsModifySupportedInParallelMode(CmdType commandType)
+{
+	/* Currently only INSERT is supported */
+	return (commandType == CMD_INSERT);
+}
 
 #endif							/* XACT_H */

src/include/nodes/pathnodes.h

@@ -120,6 +120,8 @@ typedef struct PlannerGlobal
 
 	List	   *relationOids;	/* OIDs of relations the plan depends on */
 
+	List	   *partitionOids;	/* OIDs of partitions the plan depends on */
+
 	List	   *invalItems;		/* other dependencies, as PlanInvalItems */
 
 	List	   *paramExecTypes; /* type OIDs for PARAM_EXEC Params */

src/include/nodes/plannodes.h

@@ -79,6 +79,8 @@ typedef struct PlannedStmt
 
 	List	   *relationOids;	/* OIDs of relations the plan depends on */
 
+	List	   *partitionOids;	/* OIDs of partitions the plan depends on */
+
 	List	   *invalItems;		/* other dependencies, as PlanInvalItems */
 
 	List	   *paramExecTypes; /* type OIDs for PARAM_EXEC Params */

src/include/optimizer/clauses.h

@@ -32,7 +32,7 @@ extern double expression_returns_set_rows(PlannerInfo *root, Node *clause);
 
 extern bool contain_subplans(Node *clause);
 
-extern char max_parallel_hazard(Query *parse);
+extern char max_parallel_hazard(Query *parse, PlannerGlobal *glob);
 extern bool is_parallel_safe(PlannerInfo *root, Node *node);
 extern bool contain_nonstrict_functions(Node *clause);
 extern bool contain_exec_param(Node *clause, List *param_ids);
@@ -52,5 +52,6 @@ extern void CommuteOpExpr(OpExpr *clause);
 
 extern Query *inline_set_returning_function(PlannerInfo *root,
 											RangeTblEntry *rte);
+extern bool is_parallel_allowed_for_modify(Query *parse);
 
 #endif							/* CLAUSES_H */

src/test/regress/expected/insert_parallel.out

@@ -0,0 +1,536 @@
+--
+-- PARALLEL
+--
+--
+-- START: setup some tables and data needed by the tests.
+--
+-- Setup - index expressions test
+-- For testing purposes, we'll mark this function as parallel-unsafe
+create or replace function fullname_parallel_unsafe(f text, l text) returns text as $$
+    begin
+        return f || l;
+    end;
+$$ language plpgsql immutable parallel unsafe;
+create or replace function fullname_parallel_restricted(f text, l text) returns text as $$
+    begin
+        return f || l;
+    end;
+$$ language plpgsql immutable parallel restricted;
+create table names(index int, first_name text, last_name text);
+create table names2(index int, first_name text, last_name text);
+create index names2_fullname_idx on names2 (fullname_parallel_unsafe(first_name, last_name));
+create table names4(index int, first_name text, last_name text);
+create index names4_fullname_idx on names4 (fullname_parallel_restricted(first_name, last_name));
+insert into names values
+	(1, 'albert', 'einstein'),
+	(2, 'niels', 'bohr'),
+	(3, 'erwin', 'schrodinger'),
+	(4, 'leonhard', 'euler'),
+	(5, 'stephen', 'hawking'),
+	(6, 'isaac', 'newton'),
+	(7, 'alan', 'turing'),
+	(8, 'richard', 'feynman');
+-- Setup - column default tests
+create or replace function bdefault_unsafe ()
+returns int language plpgsql parallel unsafe as $$
+begin
+	RETURN 5;
+end $$;
+create or replace function cdefault_restricted ()
+returns int language plpgsql parallel restricted as $$
+begin
+	RETURN 10;
+end $$;
+create or replace function ddefault_safe ()
+returns int language plpgsql parallel safe as $$
+begin
+	RETURN 20;
+end $$;
+create table testdef(a int, b int default bdefault_unsafe(), c int default cdefault_restricted(), d int default ddefault_safe());
+create table test_data(a int);
+insert into test_data select * from generate_series(1,10);
+--
+-- END: setup some tables and data needed by the tests.
+--
+-- Serializable isolation would disable parallel query, so explicitly use an
+-- arbitrary other level.
+begin isolation level repeatable read;
+-- encourage use of parallel plans
+set parallel_setup_cost=0;
+set parallel_tuple_cost=0;
+set min_parallel_table_scan_size=0;
+set max_parallel_workers_per_gather=4;
+create table para_insert_p1 (
+	unique1		int4	PRIMARY KEY,
+	stringu1	name
+);
+create table para_insert_f1 (
+	unique1		int4	REFERENCES para_insert_p1(unique1),
+	stringu1	name
+);
+--
+-- Test INSERT with underlying query.
+-- (should create plan with parallel SELECT, Gather parent node)
+--
+explain (costs off) insert into para_insert_p1 select unique1, stringu1 from tenk1;
+               QUERY PLAN               
+----------------------------------------
+ Insert on para_insert_p1
+   ->  Gather
+         Workers Planned: 4
+         ->  Parallel Seq Scan on tenk1
+(4 rows)
+
+insert into para_insert_p1 select unique1, stringu1 from tenk1;
+-- select some values to verify that the parallel insert worked
+select count(*), sum(unique1) from para_insert_p1;
+ count |   sum    
+-------+----------
+ 10000 | 49995000
+(1 row)
+
+-- verify that the same transaction has been used by all parallel workers
+select count(*) from (select distinct cmin,xmin from para_insert_p1) as dt;
+ count 
+-------
+     1
+(1 row)
+
+--
+-- Test INSERT with ordered underlying query.
+-- (should create plan with parallel SELECT, GatherMerge parent node)
+--
+truncate para_insert_p1 cascade;
+NOTICE:  truncate cascades to table "para_insert_f1"
+explain (costs off) insert into para_insert_p1 select unique1, stringu1 from tenk1 order by unique1;
+                  QUERY PLAN                  
+----------------------------------------------
+ Insert on para_insert_p1
+   ->  Gather Merge
+         Workers Planned: 4
+         ->  Sort
+               Sort Key: tenk1.unique1
+               ->  Parallel Seq Scan on tenk1
+(6 rows)
+
+insert into para_insert_p1 select unique1, stringu1 from tenk1 order by unique1;
+-- select some values to verify that the parallel insert worked
+select count(*), sum(unique1) from para_insert_p1;
+ count |   sum    
+-------+----------
+ 10000 | 49995000
+(1 row)
+
+-- verify that the same transaction has been used by all parallel workers
+select count(*) from (select distinct cmin,xmin from para_insert_p1) as dt;
+ count 
+-------
+     1
+(1 row)
+
+--
+-- Test INSERT with RETURNING clause.
+-- (should create plan with parallel SELECT, Gather parent node)
+--
+create table test_data1(like test_data);
+explain (costs off) insert into test_data1 select * from test_data where a = 10 returning a as data;
+                 QUERY PLAN                 
+--------------------------------------------
+ Insert on test_data1
+   ->  Gather
+         Workers Planned: 3
+         ->  Parallel Seq Scan on test_data
+               Filter: (a = 10)
+(5 rows)
+
+insert into test_data1 select * from test_data where a = 10 returning a as data;
+ data 
+------
+   10
+(1 row)
+
+--
+-- Test INSERT into a table with a foreign key.
+-- (Insert into a table with a foreign key is parallel-restricted,
+--  as doing this in a parallel worker would create a new commandId
+--  and within a worker this is not currently supported)
+--
+explain (costs off) insert into para_insert_f1 select unique1, stringu1 from tenk1;
+               QUERY PLAN               
+----------------------------------------
+ Insert on para_insert_f1
+   ->  Gather
+         Workers Planned: 4
+         ->  Parallel Seq Scan on tenk1
+(4 rows)
+
+insert into para_insert_f1 select unique1, stringu1 from tenk1;
+-- select some values to verify that the insert worked
+select count(*), sum(unique1) from para_insert_f1;
+ count |   sum    
+-------+----------
+ 10000 | 49995000
+(1 row)
+
+--
+-- Test INSERT with ON CONFLICT ... DO UPDATE ...
+-- (should not create a parallel plan)
+--
+create table test_conflict_table(id serial primary key, somedata int);
+explain (costs off) insert into test_conflict_table(id, somedata) select a, a from test_data;
+                 QUERY PLAN                 
+--------------------------------------------
+ Insert on test_conflict_table
+   ->  Gather
+         Workers Planned: 3
+         ->  Parallel Seq Scan on test_data
+(4 rows)
+
+insert into test_conflict_table(id, somedata) select a, a from test_data;
+explain (costs off) insert into test_conflict_table(id, somedata) select a, a from test_data ON CONFLICT(id) DO UPDATE SET somedata = EXCLUDED.somedata + 1;
+                      QUERY PLAN                      
+------------------------------------------------------
+ Insert on test_conflict_table
+   Conflict Resolution: UPDATE
+   Conflict Arbiter Indexes: test_conflict_table_pkey
+   ->  Seq Scan on test_data
+(4 rows)
+
+--
+-- Test INSERT with parallel-unsafe index expression
+-- (should not create a parallel plan)
+--
+explain (costs off) insert into names2 select * from names;
+       QUERY PLAN        
+-------------------------
+ Insert on names2
+   ->  Seq Scan on names
+(2 rows)
+
+--
+-- Test INSERT with parallel-restricted index expression
+-- (should create a parallel plan)
+--
+explain (costs off) insert into names4 select * from names;
+               QUERY PLAN               
+----------------------------------------
+ Insert on names4
+   ->  Gather
+         Workers Planned: 3
+         ->  Parallel Seq Scan on names
+(4 rows)
+
+--
+-- Test INSERT with underlying query - and RETURNING (no projection)
+-- (should create a parallel plan; parallel SELECT)
+--
+create table names5 (like names);
+explain (costs off) insert into names5 select * from names returning *;
+               QUERY PLAN               
+----------------------------------------
+ Insert on names5
+   ->  Gather
+         Workers Planned: 3
+         ->  Parallel Seq Scan on names
+(4 rows)
+
+--
+-- Test INSERT with underlying ordered query - and RETURNING (no projection)
+-- (should create a parallel plan; parallel SELECT)
+--
+create table names6 (like names);
+explain (costs off) insert into names6 select * from names order by last_name returning *;
+                  QUERY PLAN                  
+----------------------------------------------
+ Insert on names6
+   ->  Gather Merge
+         Workers Planned: 3
+         ->  Sort
+               Sort Key: names.last_name
+               ->  Parallel Seq Scan on names
+(6 rows)
+
+insert into names6 select * from names order by last_name returning *;
+ index | first_name |  last_name  
+-------+------------+-------------
+     2 | niels      | bohr
+     1 | albert     | einstein
+     4 | leonhard   | euler
+     8 | richard    | feynman
+     5 | stephen    | hawking
+     6 | isaac      | newton
+     3 | erwin      | schrodinger
+     7 | alan       | turing
+(8 rows)
+
+--
+-- Test INSERT with underlying ordered query - and RETURNING (with projection)
+-- (should create a parallel plan; parallel SELECT)
+--
+create table names7 (like names);
+explain (costs off) insert into names7 select * from names order by last_name returning last_name || ', ' || first_name as last_name_then_first_name;
+                  QUERY PLAN                  
+----------------------------------------------
+ Insert on names7
+   ->  Gather Merge
+         Workers Planned: 3
+         ->  Sort
+               Sort Key: names.last_name
+               ->  Parallel Seq Scan on names
+(6 rows)
+
+insert into names7 select * from names order by last_name returning last_name || ', ' || first_name as last_name_then_first_name;
+ last_name_then_first_name 
+---------------------------
+ bohr, niels
+ einstein, albert
+ euler, leonhard
+ feynman, richard
+ hawking, stephen
+ newton, isaac
+ schrodinger, erwin
+ turing, alan
+(8 rows)
+
+--
+-- Test INSERT into temporary table with underlying query.
+-- (Insert into a temp table is parallel-restricted;
+-- should create a parallel plan; parallel SELECT)
+--
+create temporary table temp_names (like names);
+explain (costs off) insert into temp_names select * from names;
+               QUERY PLAN               
+----------------------------------------
+ Insert on temp_names
+   ->  Gather
+         Workers Planned: 3
+         ->  Parallel Seq Scan on names
+(4 rows)
+
+insert into temp_names select * from names;
+--
+-- Test INSERT with column defaults
+--
+--
+--
+-- Parallel unsafe column default, should not use a parallel plan
+--
+explain (costs off) insert into testdef(a,c,d) select a,a*4,a*8 from test_data;
+         QUERY PLAN          
+-----------------------------
+ Insert on testdef
+   ->  Seq Scan on test_data
+(2 rows)
+
+--
+-- Parallel restricted column default, should use parallel SELECT
+--
+explain (costs off) insert into testdef(a,b,d) select a,a*2,a*8 from test_data;
+                 QUERY PLAN                 
+--------------------------------------------
+ Insert on testdef
+   ->  Gather
+         Workers Planned: 3
+         ->  Parallel Seq Scan on test_data
+(4 rows)
+
+insert into testdef(a,b,d) select a,a*2,a*8 from test_data;
+select * from testdef order by a;
+ a  | b  | c  | d  
+----+----+----+----
+  1 |  2 | 10 |  8
+  2 |  4 | 10 | 16
+  3 |  6 | 10 | 24
+  4 |  8 | 10 | 32
+  5 | 10 | 10 | 40
+  6 | 12 | 10 | 48
+  7 | 14 | 10 | 56
+  8 | 16 | 10 | 64
+  9 | 18 | 10 | 72
+ 10 | 20 | 10 | 80
+(10 rows)
+
+truncate testdef;
+--
+-- Parallel restricted and unsafe column defaults, should not use a parallel plan
+--
+explain (costs off) insert into testdef(a,d) select a,a*8 from test_data;
+         QUERY PLAN          
+-----------------------------
+ Insert on testdef
+   ->  Seq Scan on test_data
+(2 rows)
+
+--
+-- Test INSERT into partition with underlying query.
+--
+create table parttable1 (a int, b name) partition by range (a);
+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);
+explain (costs off) insert into parttable1 select unique1,stringu1 from tenk1;
+               QUERY PLAN               
+----------------------------------------
+ Insert on parttable1
+   ->  Gather
+         Workers Planned: 4
+         ->  Parallel Seq Scan on tenk1
+(4 rows)
+
+insert into parttable1 select unique1,stringu1 from tenk1;
+select count(*) from parttable1_1;
+ count 
+-------
+  5000
+(1 row)
+
+select count(*) from parttable1_2;
+ count 
+-------
+  5000
+(1 row)
+
+--
+-- Test INSERT into table with parallel-unsafe check constraint
+-- (should not create a parallel plan)
+--
+create or replace function check_b_unsafe(b name) returns boolean as $$
+    begin
+        return (b <> 'XXXXXX');
+    end;
+$$ language plpgsql parallel unsafe;
+create table table_check_b(a int4, b name check (check_b_unsafe(b)), c name);
+explain (costs off) insert into table_check_b(a,b,c) select unique1, unique2, stringu1 from tenk1;
+       QUERY PLAN        
+-------------------------
+ Insert on table_check_b
+   ->  Seq Scan on tenk1
+(2 rows)
+
+--
+-- Test INSERT into table with parallel-safe after stmt-level triggers
+-- (should create a parallel SELECT plan; triggers should fire)
+--
+create table names_with_safe_trigger (like names);
+create or replace function insert_after_trigger_safe() returns trigger as $$
+    begin
+        raise notice 'hello from insert_after_trigger_safe';
+		return new;
+    end;
+$$ language plpgsql parallel safe;
+create trigger insert_after_trigger_safe after insert on names_with_safe_trigger
+    for each statement execute procedure insert_after_trigger_safe();
+explain (costs off) insert into names_with_safe_trigger select * from names;
+               QUERY PLAN               
+----------------------------------------
+ Insert on names_with_safe_trigger
+   ->  Gather
+         Workers Planned: 3
+         ->  Parallel Seq Scan on names
+(4 rows)
+
+insert into names_with_safe_trigger select * from names;
+NOTICE:  hello from insert_after_trigger_safe
+--
+-- Test INSERT into table with parallel-unsafe after stmt-level triggers
+-- (should not create a parallel plan; triggers should fire)
+--
+create table names_with_unsafe_trigger (like names);
+create or replace function insert_after_trigger_unsafe() returns trigger as $$
+    begin
+        raise notice 'hello from insert_after_trigger_unsafe';
+		return new;
+    end;
+$$ language plpgsql parallel unsafe;
+create trigger insert_after_trigger_unsafe after insert on names_with_unsafe_trigger
+    for each statement execute procedure insert_after_trigger_unsafe();
+explain (costs off) insert into names_with_unsafe_trigger select * from names;
+             QUERY PLAN              
+-------------------------------------
+ Insert on names_with_unsafe_trigger
+   ->  Seq Scan on names
+(2 rows)
+
+insert into names_with_unsafe_trigger select * from names;
+NOTICE:  hello from insert_after_trigger_unsafe
+--
+-- Test INSERT into partition with parallel-unsafe trigger
+-- (should not create a parallel plan)
+--
+create table part_unsafe_trigger (a int4, b name) partition by range (a);
+create table part_unsafe_trigger_1 partition of part_unsafe_trigger for values from (0) to (5000);
+create table part_unsafe_trigger_2 partition of part_unsafe_trigger for values from (5000) to (10000);
+create trigger part_insert_after_trigger_unsafe after insert on part_unsafe_trigger_1
+    for each statement execute procedure insert_after_trigger_unsafe();
+explain (costs off) insert into part_unsafe_trigger select unique1, stringu1 from tenk1;
+          QUERY PLAN           
+-------------------------------
+ Insert on part_unsafe_trigger
+   ->  Seq Scan on tenk1
+(2 rows)
+
+--
+-- Test that parallel-safety-related changes to partitions are detected and
+-- plan cache invalidation is working correctly.
+--
+create table rp (a int) partition by range (a);
+create table rp1 partition of rp for values from (minvalue) to (0);
+create table rp2 partition of rp for values from (0) to (maxvalue);
+create table foo (a) as select unique1 from tenk1;
+prepare q as insert into rp select * from foo where a%2 = 0;
+-- should create a parallel plan
+explain (costs off) execute q;
+              QUERY PLAN              
+--------------------------------------
+ Insert on rp
+   ->  Gather
+         Workers Planned: 4
+         ->  Parallel Seq Scan on foo
+               Filter: ((a % 2) = 0)
+(5 rows)
+
+create or replace function make_table_bar () returns trigger language
+plpgsql as $$ begin create table bar(); return null; end; $$ parallel unsafe;
+create trigger ai_rp2 after insert on rp2 for each row execute
+function make_table_bar();
+-- should create a non-parallel plan
+explain (costs off) execute q;
+          QUERY PLAN           
+-------------------------------
+ Insert on rp
+   ->  Seq Scan on foo
+         Filter: ((a % 2) = 0)
+(3 rows)
+
+--
+-- Test INSERT into table having a DOMAIN column with a CHECK constraint
+--
+create function sql_is_distinct_from_u(anyelement, anyelement)
+returns boolean language sql parallel unsafe
+as 'select $1 is distinct from $2 limit 1';
+create domain inotnull_u int
+  check (sql_is_distinct_from_u(value, null));
+create table dom_table_u (x inotnull_u, y int);
+-- Test INSERT into table having a DOMAIN column with parallel-unsafe CHECK constraint
+explain (costs off) insert into dom_table_u select unique1, unique2 from tenk1;
+       QUERY PLAN        
+-------------------------
+ Insert on dom_table_u
+   ->  Seq Scan on tenk1
+(2 rows)
+
+rollback;
+--
+-- Clean up anything not created in the transaction
+--
+drop table names;
+drop index names2_fullname_idx;
+drop table names2;
+drop index names4_fullname_idx;
+drop table names4;
+drop table testdef;
+drop table test_data;
+drop function bdefault_unsafe;
+drop function cdefault_restricted;
+drop function ddefault_safe;
+drop function fullname_parallel_unsafe;
+drop function fullname_parallel_restricted;

src/test/regress/parallel_schedule

@@ -90,6 +90,7 @@ test: rules psql psql_crosstab amutils stats_ext collate.linux.utf8
 # run by itself so it can run parallel workers
 test: select_parallel
 test: write_parallel
+test: insert_parallel
 
 # no relation related tests can be put in this group
 test: publication subscription

src/test/regress/serial_schedule

@@ -148,6 +148,7 @@ test: stats_ext
 test: collate.linux.utf8
 test: select_parallel
 test: write_parallel
+test: insert_parallel
 test: publication
 test: subscription
 test: select_views

src/test/regress/sql/insert_parallel.sql

@@ -0,0 +1,335 @@
+--
+-- PARALLEL
+--
+
+--
+-- START: setup some tables and data needed by the tests.
+--
+
+-- Setup - index expressions test
+
+-- For testing purposes, we'll mark this function as parallel-unsafe
+create or replace function fullname_parallel_unsafe(f text, l text) returns text as $$
+    begin
+        return f || l;
+    end;
+$$ language plpgsql immutable parallel unsafe;
+
+create or replace function fullname_parallel_restricted(f text, l text) returns text as $$
+    begin
+        return f || l;
+    end;
+$$ language plpgsql immutable parallel restricted;
+
+create table names(index int, first_name text, last_name text);
+create table names2(index int, first_name text, last_name text);
+create index names2_fullname_idx on names2 (fullname_parallel_unsafe(first_name, last_name));
+create table names4(index int, first_name text, last_name text);
+create index names4_fullname_idx on names4 (fullname_parallel_restricted(first_name, last_name));
+
+insert into names values
+	(1, 'albert', 'einstein'),
+	(2, 'niels', 'bohr'),
+	(3, 'erwin', 'schrodinger'),
+	(4, 'leonhard', 'euler'),
+	(5, 'stephen', 'hawking'),
+	(6, 'isaac', 'newton'),
+	(7, 'alan', 'turing'),
+	(8, 'richard', 'feynman');
+
+-- Setup - column default tests
+
+create or replace function bdefault_unsafe ()
+returns int language plpgsql parallel unsafe as $$
+begin
+	RETURN 5;
+end $$;
+
+create or replace function cdefault_restricted ()
+returns int language plpgsql parallel restricted as $$
+begin
+	RETURN 10;
+end $$;
+
+create or replace function ddefault_safe ()
+returns int language plpgsql parallel safe as $$
+begin
+	RETURN 20;
+end $$;
+
+create table testdef(a int, b int default bdefault_unsafe(), c int default cdefault_restricted(), d int default ddefault_safe());
+
+create table test_data(a int);
+insert into test_data select * from generate_series(1,10);
+
+--
+-- END: setup some tables and data needed by the tests.
+--
+
+-- Serializable isolation would disable parallel query, so explicitly use an
+-- arbitrary other level.
+begin isolation level repeatable read;
+
+-- encourage use of parallel plans
+set parallel_setup_cost=0;
+set parallel_tuple_cost=0;
+set min_parallel_table_scan_size=0;
+set max_parallel_workers_per_gather=4;
+
+create table para_insert_p1 (
+	unique1		int4	PRIMARY KEY,
+	stringu1	name
+);
+
+create table para_insert_f1 (
+	unique1		int4	REFERENCES para_insert_p1(unique1),
+	stringu1	name
+);
+
+
+--
+-- Test INSERT with underlying query.
+-- (should create plan with parallel SELECT, Gather parent node)
+--
+explain (costs off) insert into para_insert_p1 select unique1, stringu1 from tenk1;
+insert into para_insert_p1 select unique1, stringu1 from tenk1;
+-- select some values to verify that the parallel insert worked
+select count(*), sum(unique1) from para_insert_p1;
+-- verify that the same transaction has been used by all parallel workers
+select count(*) from (select distinct cmin,xmin from para_insert_p1) as dt;
+
+--
+-- Test INSERT with ordered underlying query.
+-- (should create plan with parallel SELECT, GatherMerge parent node)
+--
+truncate para_insert_p1 cascade;
+explain (costs off) insert into para_insert_p1 select unique1, stringu1 from tenk1 order by unique1;
+insert into para_insert_p1 select unique1, stringu1 from tenk1 order by unique1;
+-- select some values to verify that the parallel insert worked
+select count(*), sum(unique1) from para_insert_p1;
+-- verify that the same transaction has been used by all parallel workers
+select count(*) from (select distinct cmin,xmin from para_insert_p1) as dt;
+
+--
+-- Test INSERT with RETURNING clause.
+-- (should create plan with parallel SELECT, Gather parent node)
+--
+create table test_data1(like test_data);
+explain (costs off) insert into test_data1 select * from test_data where a = 10 returning a as data;
+insert into test_data1 select * from test_data where a = 10 returning a as data;
+
+--
+-- Test INSERT into a table with a foreign key.
+-- (Insert into a table with a foreign key is parallel-restricted,
+--  as doing this in a parallel worker would create a new commandId
+--  and within a worker this is not currently supported)
+--
+explain (costs off) insert into para_insert_f1 select unique1, stringu1 from tenk1;
+insert into para_insert_f1 select unique1, stringu1 from tenk1;
+-- select some values to verify that the insert worked
+select count(*), sum(unique1) from para_insert_f1;
+
+--
+-- Test INSERT with ON CONFLICT ... DO UPDATE ...
+-- (should not create a parallel plan)
+--
+create table test_conflict_table(id serial primary key, somedata int);
+explain (costs off) insert into test_conflict_table(id, somedata) select a, a from test_data;
+insert into test_conflict_table(id, somedata) select a, a from test_data;
+explain (costs off) insert into test_conflict_table(id, somedata) select a, a from test_data ON CONFLICT(id) DO UPDATE SET somedata = EXCLUDED.somedata + 1;
+
+
+--
+-- Test INSERT with parallel-unsafe index expression
+-- (should not create a parallel plan)
+--
+explain (costs off) insert into names2 select * from names;
+
+--
+-- Test INSERT with parallel-restricted index expression
+-- (should create a parallel plan)
+--
+explain (costs off) insert into names4 select * from names;
+
+--
+-- Test INSERT with underlying query - and RETURNING (no projection)
+-- (should create a parallel plan; parallel SELECT)
+--
+create table names5 (like names);
+explain (costs off) insert into names5 select * from names returning *;
+
+--
+-- Test INSERT with underlying ordered query - and RETURNING (no projection)
+-- (should create a parallel plan; parallel SELECT)
+--
+create table names6 (like names);
+explain (costs off) insert into names6 select * from names order by last_name returning *;
+insert into names6 select * from names order by last_name returning *;
+
+--
+-- Test INSERT with underlying ordered query - and RETURNING (with projection)
+-- (should create a parallel plan; parallel SELECT)
+--
+create table names7 (like names);
+explain (costs off) insert into names7 select * from names order by last_name returning last_name || ', ' || first_name as last_name_then_first_name;
+insert into names7 select * from names order by last_name returning last_name || ', ' || first_name as last_name_then_first_name;
+
+
+--
+-- Test INSERT into temporary table with underlying query.
+-- (Insert into a temp table is parallel-restricted;
+-- should create a parallel plan; parallel SELECT)
+--
+create temporary table temp_names (like names);
+explain (costs off) insert into temp_names select * from names;
+insert into temp_names select * from names;
+
+--
+-- Test INSERT with column defaults
+--
+--
+
+--
+-- Parallel unsafe column default, should not use a parallel plan
+--
+explain (costs off) insert into testdef(a,c,d) select a,a*4,a*8 from test_data;
+
+--
+-- Parallel restricted column default, should use parallel SELECT
+--
+explain (costs off) insert into testdef(a,b,d) select a,a*2,a*8 from test_data;
+insert into testdef(a,b,d) select a,a*2,a*8 from test_data;
+select * from testdef order by a;
+truncate testdef;
+
+--
+-- Parallel restricted and unsafe column defaults, should not use a parallel plan
+--
+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_1 partition of parttable1 for values from (0) to (5000);
+create table parttable1_2 partition of parttable1 for values from (5000) to (10000);
+
+explain (costs off) insert into parttable1 select unique1,stringu1 from tenk1;
+insert into parttable1 select unique1,stringu1 from tenk1;
+select count(*) from parttable1_1;
+select count(*) from parttable1_2;
+
+--
+-- Test INSERT into table with parallel-unsafe check constraint
+-- (should not create a parallel plan)
+--
+create or replace function check_b_unsafe(b name) returns boolean as $$
+    begin
+        return (b <> 'XXXXXX');
+    end;
+$$ language plpgsql parallel unsafe;
+
+create table table_check_b(a int4, b name check (check_b_unsafe(b)), c name);
+explain (costs off) insert into table_check_b(a,b,c) select unique1, unique2, stringu1 from tenk1;
+
+--
+-- Test INSERT into table with parallel-safe after stmt-level triggers
+-- (should create a parallel SELECT plan; triggers should fire)
+--
+create table names_with_safe_trigger (like names);
+create or replace function insert_after_trigger_safe() returns trigger as $$
+    begin
+        raise notice 'hello from insert_after_trigger_safe';
+		return new;
+    end;
+$$ language plpgsql parallel safe;
+create trigger insert_after_trigger_safe after insert on names_with_safe_trigger
+    for each statement execute procedure insert_after_trigger_safe();
+explain (costs off) insert into names_with_safe_trigger select * from names;
+insert into names_with_safe_trigger select * from names;
+
+--
+-- Test INSERT into table with parallel-unsafe after stmt-level triggers
+-- (should not create a parallel plan; triggers should fire)
+--
+create table names_with_unsafe_trigger (like names);
+create or replace function insert_after_trigger_unsafe() returns trigger as $$
+    begin
+        raise notice 'hello from insert_after_trigger_unsafe';
+		return new;
+    end;
+$$ language plpgsql parallel unsafe;
+create trigger insert_after_trigger_unsafe after insert on names_with_unsafe_trigger
+    for each statement execute procedure insert_after_trigger_unsafe();
+explain (costs off) insert into names_with_unsafe_trigger select * from names;
+insert into names_with_unsafe_trigger select * from names;
+
+--
+-- Test INSERT into partition with parallel-unsafe trigger
+-- (should not create a parallel plan)
+--
+
+create table part_unsafe_trigger (a int4, b name) partition by range (a);
+create table part_unsafe_trigger_1 partition of part_unsafe_trigger for values from (0) to (5000);
+create table part_unsafe_trigger_2 partition of part_unsafe_trigger for values from (5000) to (10000);
+create trigger part_insert_after_trigger_unsafe after insert on part_unsafe_trigger_1
+    for each statement execute procedure insert_after_trigger_unsafe();
+
+explain (costs off) insert into part_unsafe_trigger select unique1, stringu1 from tenk1;
+
+--
+-- Test that parallel-safety-related changes to partitions are detected and
+-- plan cache invalidation is working correctly.
+--
+
+create table rp (a int) partition by range (a);
+create table rp1 partition of rp for values from (minvalue) to (0);
+create table rp2 partition of rp for values from (0) to (maxvalue);
+create table foo (a) as select unique1 from tenk1;
+prepare q as insert into rp select * from foo where a%2 = 0;
+-- should create a parallel plan
+explain (costs off) execute q;
+
+create or replace function make_table_bar () returns trigger language
+plpgsql as $$ begin create table bar(); return null; end; $$ parallel unsafe;
+create trigger ai_rp2 after insert on rp2 for each row execute
+function make_table_bar();
+-- should create a non-parallel plan
+explain (costs off) execute q;
+
+--
+-- Test INSERT into table having a DOMAIN column with a CHECK constraint
+--
+create function sql_is_distinct_from_u(anyelement, anyelement)
+returns boolean language sql parallel unsafe
+as 'select $1 is distinct from $2 limit 1';
+
+create domain inotnull_u int
+  check (sql_is_distinct_from_u(value, null));
+
+create table dom_table_u (x inotnull_u, y int);
+
+
+-- Test INSERT into table having a DOMAIN column with parallel-unsafe CHECK constraint
+explain (costs off) insert into dom_table_u select unique1, unique2 from tenk1;
+
+
+rollback;
+
+--
+-- Clean up anything not created in the transaction
+--
+
+drop table names;
+drop index names2_fullname_idx;
+drop table names2;
+drop index names4_fullname_idx;
+drop table names4;
+drop table testdef;
+drop table test_data;
+
+drop function bdefault_unsafe;
+drop function cdefault_restricted;
+drop function ddefault_safe;
+drop function fullname_parallel_unsafe;
+drop function fullname_parallel_restricted;