pq_pushdown_initplan_v11.patch

diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index 8f7062c..561b85c 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -107,6 +107,7 @@ static void show_tidbitmap_info(BitmapHeapScanState *planstate,
 static void show_instrumentation_count(const char *qlabel, int which,
 						   PlanState *planstate, ExplainState *es);
 static void show_foreignscan_info(ForeignScanState *fsstate, ExplainState *es);
+static void show_eval_params(Bitmapset *bms_params, ExplainState *es);
 static const char *explain_get_index_name(Oid indexId);
 static void show_buffer_usage(ExplainState *es, const BufferUsage *usage);
 static void ExplainIndexScanDetails(Oid indexid, ScanDirection indexorderdir,
@@ -631,7 +632,21 @@ ExplainPrintPlan(ExplainState *es, QueryDesc *queryDesc)
 	 */
 	ps = queryDesc->planstate;
 	if (IsA(ps, GatherState) &&((Gather *) ps->plan)->invisible)
+	{
+		List	   *initPlanState = NULL;
+		PlanState  *save_ps;
+
+		/*
+		 * The Gather node will be omitted in this case, so we need to move
+		 * initplans to the outer node to ensure that they remain attached to
+		 * the top node (cf standard_planner).
+		 */
+		save_ps = ps;
+		initPlanState = ps->initPlan;
 		ps = outerPlanState(ps);
+		ps->initPlan = initPlanState;
+		save_ps->initPlan = NIL;
+	}
 	ExplainNode(ps, NIL, NULL, NULL, es);
 }
 
@@ -1441,6 +1456,11 @@ ExplainNode(PlanState *planstate, List *ancestors,
 											   planstate, es);
 				ExplainPropertyInteger("Workers Planned",
 									   gather->num_workers, es);
+
+				/* Show params evaluated at gather node */
+				if (gather->initParam)
+					show_eval_params(gather->initParam, es);
+
 				if (es->analyze)
 				{
 					int			nworkers;
@@ -1463,6 +1483,11 @@ ExplainNode(PlanState *planstate, List *ancestors,
 											   planstate, es);
 				ExplainPropertyInteger("Workers Planned",
 									   gm->num_workers, es);
+
+				/* Show params evaluated at gather-merge node */
+				if (gm->initParam)
+					show_eval_params(gm->initParam, es);
+
 				if (es->analyze)
 				{
 					int			nworkers;
@@ -2488,6 +2513,29 @@ show_foreignscan_info(ForeignScanState *fsstate, ExplainState *es)
 }
 
 /*
+ * Show initplan params evaluated at Gather or Gather Merge node.
+ */
+static void
+show_eval_params(Bitmapset *bms_params, ExplainState *es)
+{
+	int			paramid = -1;
+	List	   *params = NIL;
+
+	Assert(bms_params);
+
+	while ((paramid = bms_next_member(bms_params, paramid)) >= 0)
+	{
+		char		param[32];
+
+		snprintf(param, sizeof(param), "$%d", paramid);
+		params = lappend(params, pstrdup(param));
+	}
+
+	if (params)
+		ExplainPropertyList("Params Evaluated", params, es);
+}
+
+/*
  * Fetch the name of an index in an EXPLAIN
  *
  * We allow plugins to get control here so that plans involving hypothetical
diff --git a/src/backend/executor/execExprInterp.c b/src/backend/executor/execExprInterp.c
index c5e97ef..d170f305 100644
--- a/src/backend/executor/execExprInterp.c
+++ b/src/backend/executor/execExprInterp.c
@@ -1927,6 +1927,33 @@ ExecEvalParamExec(ExprState *state, ExprEvalStep *op, ExprContext *econtext)
 }
 
 /*
+ * ExecEvalParamExecParams
+ *
+ * Execute the subplan stored in PARAM_EXEC initplans params, if not executed
+ * till now.
+ */
+void
+ExecEvalParamExecParams(Bitmapset *params, EState *estate)
+{
+	ParamExecData *prm;
+	int			paramid;
+
+	paramid = -1;
+	while ((paramid = bms_next_member(params, paramid)) >= 0)
+	{
+		prm = &(estate->es_param_exec_vals[paramid]);
+
+		if (prm->execPlan != NULL)
+		{
+			/* Parameter not evaluated yet, so go do it */
+			ExecSetParamPlan(prm->execPlan, GetPerTupleExprContext(estate));
+			/* ExecSetParamPlan should have processed this param... */
+			Assert(prm->execPlan == NULL);
+		}
+	}
+}
+
+/*
  * Evaluate a PARAM_EXTERN parameter.
  *
  * PARAM_EXTERN parameters must be sought in ecxt_param_list_info.
diff --git a/src/backend/executor/execParallel.c b/src/backend/executor/execParallel.c
index 5dc26ed..57a8fe5 100644
--- a/src/backend/executor/execParallel.c
+++ b/src/backend/executor/execParallel.c
@@ -23,6 +23,7 @@
 
 #include "postgres.h"
 
+#include "executor/execExpr.h"
 #include "executor/execParallel.h"
 #include "executor/executor.h"
 #include "executor/nodeBitmapHeapscan.h"
@@ -31,6 +32,7 @@
 #include "executor/nodeIndexscan.h"
 #include "executor/nodeIndexonlyscan.h"
 #include "executor/nodeSeqscan.h"
+#include "executor/nodeSubplan.h"
 #include "executor/nodeSort.h"
 #include "executor/tqueue.h"
 #include "nodes/nodeFuncs.h"
@@ -56,6 +58,7 @@
 #define PARALLEL_KEY_INSTRUMENTATION	UINT64CONST(0xE000000000000006)
 #define PARALLEL_KEY_DSA				UINT64CONST(0xE000000000000007)
 #define PARALLEL_KEY_QUERY_TEXT		UINT64CONST(0xE000000000000008)
+#define PARALLEL_KEY_INITPLAN_PARAMS	UINT64CONST(0xE000000000000009)
 
 #define PARALLEL_TUPLE_QUEUE_SIZE		65536
 
@@ -395,7 +398,8 @@ ExecParallelSetupTupleQueues(ParallelContext *pcxt, bool reinitialize)
  * execution and return results to the main backend.
  */
 ParallelExecutorInfo *
-ExecInitParallelPlan(PlanState *planstate, EState *estate, int nworkers,
+ExecInitParallelPlan(PlanState *planstate, EState *estate,
+					 Bitmapset *initParam, int nworkers,
 					 int64 tuples_needed)
 {
 	ParallelExecutorInfo *pei;
@@ -406,10 +410,12 @@ ExecInitParallelPlan(PlanState *planstate, EState *estate, int nworkers,
 	char	   *pstmt_data;
 	char	   *pstmt_space;
 	char	   *param_space;
+	char	   *initplan_param_space;
 	BufferUsage *bufusage_space;
 	SharedExecutorInstrumentation *instrumentation = NULL;
 	int			pstmt_len;
 	int			param_len;
+	int			initplan_param_len;
 	int			instrumentation_len = 0;
 	int			instrument_offset = 0;
 	Size		dsa_minsize = dsa_minimum_size();
@@ -421,6 +427,8 @@ ExecInitParallelPlan(PlanState *planstate, EState *estate, int nworkers,
 	pei->finished = false;
 	pei->planstate = planstate;
 
+	ExecEvalParamExecParams(initParam, estate);
+
 	/* Fix up and serialize plan to be sent to workers. */
 	pstmt_data = ExecSerializePlan(planstate->plan, estate);
 
@@ -454,6 +462,11 @@ ExecInitParallelPlan(PlanState *planstate, EState *estate, int nworkers,
 	shm_toc_estimate_chunk(&pcxt->estimator, param_len);
 	shm_toc_estimate_keys(&pcxt->estimator, 1);
 
+	/* Estimate space for initplan params. */
+	initplan_param_len = EstimateInitPlanParamsSpace(estate->es_param_exec_vals, initParam);
+	shm_toc_estimate_chunk(&pcxt->estimator, initplan_param_len);
+	shm_toc_estimate_keys(&pcxt->estimator, 1);
+
 	/*
 	 * Estimate space for BufferUsage.
 	 *
@@ -528,6 +541,11 @@ ExecInitParallelPlan(PlanState *planstate, EState *estate, int nworkers,
 	shm_toc_insert(pcxt->toc, PARALLEL_KEY_PARAMS, param_space);
 	SerializeParamList(estate->es_param_list_info, &param_space);
 
+	/* Store serialized initplan params. */
+	initplan_param_space = shm_toc_allocate(pcxt->toc, initplan_param_len);
+	shm_toc_insert(pcxt->toc, PARALLEL_KEY_INITPLAN_PARAMS, initplan_param_space);
+	SerializeInitPlanParams(estate->es_param_exec_vals, initParam, &initplan_param_space);
+
 	/* Allocate space for each worker's BufferUsage; no need to initialize. */
 	bufusage_space = shm_toc_allocate(pcxt->toc,
 									  mul_size(sizeof(BufferUsage), pcxt->nworkers));
@@ -862,6 +880,21 @@ ExecParallelGetReceiver(dsm_segment *seg, shm_toc *toc)
 }
 
 /*
+ * Copy the ParamExecData params corresponding to initplans from dynamic
+ * shared memory.  This has to be done once the params are allocated by
+ * executor; that is after ExecutorStart().
+ */
+static void
+ExecParallelInitializeInitPlanParams(shm_toc *toc, ParamExecData *params)
+{
+	char	   *paramspace;
+
+	/* Reconstruct initplan params. */
+	paramspace = shm_toc_lookup(toc, PARALLEL_KEY_INITPLAN_PARAMS, false);
+	RestoreInitPlanParams(&paramspace, params);
+}
+
+/*
  * Create a QueryDesc for the PlannedStmt we are to execute, and return it.
  */
 static QueryDesc *
@@ -1046,6 +1079,7 @@ ParallelQueryMain(dsm_segment *seg, shm_toc *toc)
 
 	/* Special executor initialization steps for parallel workers */
 	queryDesc->planstate->state->es_query_dsa = area;
+	ExecParallelInitializeInitPlanParams(toc, queryDesc->estate->es_param_exec_vals);
 	ExecParallelInitializeWorker(queryDesc->planstate, toc);
 
 	/* Pass down any tuple bound */
diff --git a/src/backend/executor/nodeGather.c b/src/backend/executor/nodeGather.c
index 8370037..4104dc2 100644
--- a/src/backend/executor/nodeGather.c
+++ b/src/backend/executor/nodeGather.c
@@ -158,6 +158,7 @@ ExecGather(PlanState *pstate)
 			if (!node->pei)
 				node->pei = ExecInitParallelPlan(node->ps.lefttree,
 												 estate,
+												 gather->initParam,
 												 gather->num_workers,
 												 node->tuples_needed);
 			else
diff --git a/src/backend/executor/nodeGatherMerge.c b/src/backend/executor/nodeGatherMerge.c
index 70f33a9..f75430e 100644
--- a/src/backend/executor/nodeGatherMerge.c
+++ b/src/backend/executor/nodeGatherMerge.c
@@ -202,6 +202,7 @@ ExecGatherMerge(PlanState *pstate)
 			if (!node->pei)
 				node->pei = ExecInitParallelPlan(node->ps.lefttree,
 												 estate,
+												 gm->initParam,
 												 gm->num_workers,
 												 node->tuples_needed);
 			else
diff --git a/src/backend/executor/nodeNestloop.c b/src/backend/executor/nodeNestloop.c
index 4447b7c..52514e4 100644
--- a/src/backend/executor/nodeNestloop.c
+++ b/src/backend/executor/nodeNestloop.c
@@ -130,6 +130,7 @@ ExecNestLoop(PlanState *pstate)
 			{
 				NestLoopParam *nlp = (NestLoopParam *) lfirst(lc);
 				int			paramno = nlp->paramno;
+				TupleDesc	tdesc = outerTupleSlot->tts_tupleDescriptor;
 				ParamExecData *prm;
 
 				prm = &(econtext->ecxt_param_exec_vals[paramno]);
@@ -140,6 +141,7 @@ ExecNestLoop(PlanState *pstate)
 				prm->value = slot_getattr(outerTupleSlot,
 										  nlp->paramval->varattno,
 										  &(prm->isnull));
+				prm->ptype = TupleDescAttr(tdesc, nlp->paramval->varattno - 1)->atttypid;
 				/* Flag parameter value as changed */
 				innerPlan->chgParam = bms_add_member(innerPlan->chgParam,
 													 paramno);
diff --git a/src/backend/executor/nodeSubplan.c b/src/backend/executor/nodeSubplan.c
index 77ef6f3..06409ed 100644
--- a/src/backend/executor/nodeSubplan.c
+++ b/src/backend/executor/nodeSubplan.c
@@ -30,12 +30,16 @@
 #include <math.h>
 
 #include "access/htup_details.h"
+#include "catalog/pg_type.h"
 #include "executor/executor.h"
 #include "executor/nodeSubplan.h"
 #include "nodes/makefuncs.h"
+#include "nodes/nodeFuncs.h"
 #include "miscadmin.h"
 #include "optimizer/clauses.h"
+#include "storage/shmem.h"
 #include "utils/array.h"
+#include "utils/datum.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 
@@ -273,11 +277,13 @@ ExecScanSubPlan(SubPlanState *node,
 	forboth(l, subplan->parParam, pvar, node->args)
 	{
 		int			paramid = lfirst_int(l);
+		ExprState  *exprstate = (ExprState *) lfirst(pvar);
 		ParamExecData *prm = &(econtext->ecxt_param_exec_vals[paramid]);
 
-		prm->value = ExecEvalExprSwitchContext((ExprState *) lfirst(pvar),
+		prm->value = ExecEvalExprSwitchContext(exprstate,
 											   econtext,
 											   &(prm->isnull));
+		prm->ptype = exprType((Node *) exprstate->expr);
 		planstate->chgParam = bms_add_member(planstate->chgParam, paramid);
 	}
 
@@ -390,6 +396,7 @@ ExecScanSubPlan(SubPlanState *node,
 			prmdata = &(econtext->ecxt_param_exec_vals[paramid]);
 			Assert(prmdata->execPlan == NULL);
 			prmdata->value = slot_getattr(slot, col, &(prmdata->isnull));
+			prmdata->ptype = TupleDescAttr(tdesc, col - 1)->atttypid;
 			col++;
 		}
 
@@ -556,11 +563,13 @@ buildSubPlanHash(SubPlanState *node, ExprContext *econtext)
 		{
 			int			paramid = lfirst_int(plst);
 			ParamExecData *prmdata;
+			TupleDesc	tdesc = slot->tts_tupleDescriptor;
 
 			prmdata = &(innerecontext->ecxt_param_exec_vals[paramid]);
 			Assert(prmdata->execPlan == NULL);
 			prmdata->value = slot_getattr(slot, col,
 										  &(prmdata->isnull));
+			prmdata->ptype = TupleDescAttr(tdesc, col - 1)->atttypid;
 			col++;
 		}
 		slot = ExecProject(node->projRight);
@@ -924,6 +933,7 @@ ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
 	ListCell   *l;
 	bool		found = false;
 	ArrayBuildStateAny *astate = NULL;
+	Oid			ptype;
 
 	if (subLinkType == ANY_SUBLINK ||
 		subLinkType == ALL_SUBLINK)
@@ -931,6 +941,8 @@ ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
 	if (subLinkType == CTE_SUBLINK)
 		elog(ERROR, "CTE subplans should not be executed via ExecSetParamPlan");
 
+	ptype = exprType((Node *) node->subplan);
+
 	/* Initialize ArrayBuildStateAny in caller's context, if needed */
 	if (subLinkType == ARRAY_SUBLINK)
 		astate = initArrayResultAny(subplan->firstColType,
@@ -953,11 +965,13 @@ ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
 	forboth(l, subplan->parParam, pvar, node->args)
 	{
 		int			paramid = lfirst_int(l);
+		ExprState  *exprstate = (ExprState *) lfirst(pvar);
 		ParamExecData *prm = &(econtext->ecxt_param_exec_vals[paramid]);
 
-		prm->value = ExecEvalExprSwitchContext((ExprState *) lfirst(pvar),
+		prm->value = ExecEvalExprSwitchContext(exprstate,
 											   econtext,
 											   &(prm->isnull));
+		prm->ptype = exprType((Node *) exprstate->expr);
 		planstate->chgParam = bms_add_member(planstate->chgParam, paramid);
 	}
 
@@ -980,6 +994,7 @@ ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
 
 			prm->execPlan = NULL;
 			prm->value = BoolGetDatum(true);
+			prm->ptype = ptype;
 			prm->isnull = false;
 			found = true;
 			break;
@@ -1031,6 +1046,7 @@ ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
 			prm->execPlan = NULL;
 			prm->value = heap_getattr(node->curTuple, i, tdesc,
 									  &(prm->isnull));
+			prm->ptype = TupleDescAttr(tdesc, i - 1)->atttypid;
 			i++;
 		}
 	}
@@ -1053,6 +1069,7 @@ ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
 											true);
 		prm->execPlan = NULL;
 		prm->value = node->curArray;
+		prm->ptype = ptype;
 		prm->isnull = false;
 	}
 	else if (!found)
@@ -1065,6 +1082,7 @@ ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
 
 			prm->execPlan = NULL;
 			prm->value = BoolGetDatum(false);
+			prm->ptype = ptype;
 			prm->isnull = false;
 		}
 		else
@@ -1077,6 +1095,7 @@ ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
 
 				prm->execPlan = NULL;
 				prm->value = (Datum) 0;
+				prm->ptype = VOIDOID;
 				prm->isnull = true;
 			}
 		}
@@ -1207,3 +1226,133 @@ ExecAlternativeSubPlan(AlternativeSubPlanState *node,
 
 	return ExecSubPlan(activesp, econtext, isNull);
 }
+
+/*
+ * Estimate the amount of space required to serialize the InitPlan params.
+ */
+Size
+EstimateInitPlanParamsSpace(ParamExecData *paramExecVals, Bitmapset *params)
+{
+	int			paramid;
+	Size		sz = sizeof(int);
+	ParamExecData *prm;
+
+	if (params == NULL)
+		return sz;
+
+	paramid = -1;
+	while ((paramid = bms_next_member(params, paramid)) >= 0)
+	{
+		Oid			typeOid;
+		int16		typLen;
+		bool		typByVal;
+
+		prm = &(paramExecVals[paramid]);
+		typeOid = prm->ptype;
+
+		sz = add_size(sz, sizeof(int)); /* space for paramid */
+		sz = add_size(sz, sizeof(Oid)); /* space for type OID */
+
+		/* space for datum/isnull */
+		if (OidIsValid(typeOid))
+			get_typlenbyval(typeOid, &typLen, &typByVal);
+		else
+		{
+			/* If no type OID, assume by-value, like copyParamList does. */
+			typLen = sizeof(Datum);
+			typByVal = true;
+		}
+		sz = add_size(sz,
+					  datumEstimateSpace(prm->value, prm->isnull, typByVal, typLen));
+	}
+	return sz;
+}
+
+/*
+ * Serialize ParamExecData params corresponding to initplans.
+ *
+ * We write the number of parameters first, as a 4-byte integer, and then
+ * write details for each parameter in turn.  The details for each parameter
+ * consist of a 4-byte paramid (location of param in execution time internal
+ * parameter array), 4-byte type OID, and then the datum as serialized by
+ * datumSerialize().
+ *
+ * The above format is quite similar to the format used to serialize
+ * paramListInfo structure, so if we change either format, then consider to
+ * change at both the places.
+ */
+void
+SerializeInitPlanParams(ParamExecData *paramExecVals, Bitmapset *params,
+						char **start_address)
+{
+	int			nparams;
+	int			paramid;
+	ParamExecData *prm;
+
+	nparams = bms_num_members(params);
+	memcpy(*start_address, &nparams, sizeof(int));
+	*start_address += sizeof(int);
+
+	paramid = -1;
+	while ((paramid = bms_next_member(params, paramid)) >= 0)
+	{
+		Oid			typeOid;
+		int16		typLen;
+		bool		typByVal;
+
+		prm = &(paramExecVals[paramid]);
+		typeOid = prm->ptype;
+
+		/* Write paramid. */
+		memcpy(*start_address, &paramid, sizeof(int));
+		*start_address += sizeof(int);
+
+		/* Write OID. */
+		memcpy(*start_address, &typeOid, sizeof(Oid));
+		*start_address += sizeof(Oid);
+
+		/* space for datum/isnull */
+		if (OidIsValid(typeOid))
+			get_typlenbyval(typeOid, &typLen, &typByVal);
+		else
+		{
+			/* If no type OID, assume by-value, like copyParamList does. */
+			typLen = sizeof(Datum);
+			typByVal = true;
+		}
+		datumSerialize(prm->value, prm->isnull, typByVal, typLen,
+					   start_address);
+	}
+}
+
+/*
+ * Restore ParamExecData params corresponding to initplans.
+ */
+void
+RestoreInitPlanParams(char **start_address, ParamExecData *params)
+{
+	int			nparams;
+	int			i;
+	int			paramid;
+
+	memcpy(&nparams, *start_address, sizeof(int));
+	*start_address += sizeof(int);
+
+	for (i = 0; i < nparams; i++)
+	{
+		ParamExecData *prm;
+
+		/* Read paramid */
+		memcpy(&paramid, *start_address, sizeof(int));
+		*start_address += sizeof(int);
+		prm = &params[paramid];
+
+		/* Read type OID. */
+		memcpy(&prm->ptype, *start_address, sizeof(Oid));
+		*start_address += sizeof(Oid);
+
+		/* Read datum/isnull. */
+		prm->value = datumRestore(start_address, &prm->isnull);
+		prm->execPlan = NULL;
+	}
+}
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index c1a83ca..61fe226 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -364,6 +364,7 @@ _copyGather(const Gather *from)
 	COPY_SCALAR_FIELD(rescan_param);
 	COPY_SCALAR_FIELD(single_copy);
 	COPY_SCALAR_FIELD(invisible);
+	COPY_BITMAPSET_FIELD(initParam);
 
 	return newnode;
 }
@@ -391,6 +392,7 @@ _copyGatherMerge(const GatherMerge *from)
 	COPY_POINTER_FIELD(sortOperators, from->numCols * sizeof(Oid));
 	COPY_POINTER_FIELD(collations, from->numCols * sizeof(Oid));
 	COPY_POINTER_FIELD(nullsFirst, from->numCols * sizeof(bool));
+	COPY_BITMAPSET_FIELD(initParam);
 
 	return newnode;
 }
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 2532edc..556d533 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -482,6 +482,7 @@ _outGather(StringInfo str, const Gather *node)
 	WRITE_INT_FIELD(rescan_param);
 	WRITE_BOOL_FIELD(single_copy);
 	WRITE_BOOL_FIELD(invisible);
+	WRITE_BITMAPSET_FIELD(initParam);
 }
 
 static void
@@ -512,6 +513,8 @@ _outGatherMerge(StringInfo str, const GatherMerge *node)
 	appendStringInfoString(str, " :nullsFirst");
 	for (i = 0; i < node->numCols; i++)
 		appendStringInfo(str, " %s", booltostr(node->nullsFirst[i]));
+
+	WRITE_BITMAPSET_FIELD(initParam);
 }
 
 static void
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index 07ba691..c3bcf47 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -2165,6 +2165,7 @@ _readGather(void)
 	READ_INT_FIELD(rescan_param);
 	READ_BOOL_FIELD(single_copy);
 	READ_BOOL_FIELD(invisible);
+	READ_BITMAPSET_FIELD(initParam);
 
 	READ_DONE();
 }
@@ -2186,6 +2187,7 @@ _readGatherMerge(void)
 	READ_OID_ARRAY(sortOperators, local_node->numCols);
 	READ_OID_ARRAY(collations, local_node->numCols);
 	READ_BOOL_ARRAY(nullsFirst, local_node->numCols);
+	READ_BITMAPSET_FIELD(initParam);
 
 	READ_DONE();
 }
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index a7866a9..a2053e0 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -39,6 +39,7 @@
 #include "optimizer/planner.h"
 #include "optimizer/prep.h"
 #include "optimizer/restrictinfo.h"
+#include "optimizer/subselect.h"
 #include "optimizer/tlist.h"
 #include "optimizer/var.h"
 #include "parser/parse_clause.h"
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 2821662..0363d68 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -6257,6 +6257,7 @@ make_gather(List *qptlist,
 	node->rescan_param = rescan_param;
 	node->single_copy = single_copy;
 	node->invisible = false;
+	node->initParam = NULL;
 
 	return node;
 }
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index e7ac11e..02aa044 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -376,6 +376,14 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	{
 		Gather	   *gather = makeNode(Gather);
 
+		/*
+		 * If there are any initPlans attached to the formerly-top plan node,
+		 * move them up to the Gather node; same as we do for Material node in
+		 * materialize_finished_plan.
+		 */
+		gather->plan.initPlan = top_plan->initPlan;
+		top_plan->initPlan = NIL;
+
 		gather->plan.targetlist = top_plan->targetlist;
 		gather->plan.qual = NIL;
 		gather->plan.lefttree = top_plan;
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
index dee4414..97baa72 100644
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -104,6 +104,7 @@ static Node *fix_scan_expr_mutator(Node *node, fix_scan_expr_context *context);
 static bool fix_scan_expr_walker(Node *node, fix_scan_expr_context *context);
 static void set_join_references(PlannerInfo *root, Join *join, int rtoffset);
 static void set_upper_references(PlannerInfo *root, Plan *plan, int rtoffset);
+static void set_param_references(PlannerInfo *root, Plan *plan);
 static Node *convert_combining_aggrefs(Node *node, void *context);
 static void set_dummy_tlist_references(Plan *plan, int rtoffset);
 static indexed_tlist *build_tlist_index(List *tlist);
@@ -628,7 +629,10 @@ set_plan_refs(PlannerInfo *root, Plan *plan, int rtoffset)
 
 		case T_Gather:
 		case T_GatherMerge:
-			set_upper_references(root, plan, rtoffset);
+			{
+				set_upper_references(root, plan, rtoffset);
+				set_param_references(root, plan);
+			}
 			break;
 
 		case T_Hash:
@@ -1778,6 +1782,49 @@ set_upper_references(PlannerInfo *root, Plan *plan, int rtoffset)
 }
 
 /*
+ * set_param_references
+ *	  Initialize the initParam list in Gather or Gather merge node such that
+ *	  it contains reference of all the params that needs to be evaluated
+ *	  before execution of the node.  It contains the initplan params that are
+ *	  being passed to the plan nodes below it.
+ */
+static void
+set_param_references(PlannerInfo *root, Plan *plan)
+{
+	Assert(IsA(plan, Gather) || IsA(plan, GatherMerge));
+
+	if (plan->lefttree->extParam)
+	{
+		PlannerInfo *proot;
+		Bitmapset  *initSetParam = NULL;
+		ListCell   *l;
+
+		for (proot = root; proot != NULL; proot = proot->parent_root)
+		{
+			foreach(l, proot->init_plans)
+			{
+				SubPlan    *initsubplan = (SubPlan *) lfirst(l);
+				ListCell   *l2;
+
+				foreach(l2, initsubplan->setParam)
+				{
+					initSetParam = bms_add_member(initSetParam, lfirst_int(l2));
+				}
+			}
+		}
+
+		/*
+		 * Remember the list of all external initplan params that are used by
+		 * the children of Gather or Gather merge node.
+		 */
+		if (IsA(plan, Gather))
+			((Gather *) plan)->initParam = bms_intersect(plan->lefttree->extParam, initSetParam);
+		else
+			((GatherMerge *) plan)->initParam = bms_intersect(plan->lefttree->extParam, initSetParam);
+	}
+}
+
+/*
  * Recursively scan an expression tree and convert Aggrefs to the proper
  * intermediate form for combining aggregates.  This means (1) replacing each
  * one's argument list with a single argument that is the original Aggref
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 7961362..e1b139a 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -1087,6 +1087,8 @@ bool
 is_parallel_safe(PlannerInfo *root, Node *node)
 {
 	max_parallel_hazard_context context;
+	PlannerInfo *proot;
+	ListCell   *l;
 
 	/*
 	 * Even if the original querytree contained nothing unsafe, we need to
@@ -1101,6 +1103,25 @@ is_parallel_safe(PlannerInfo *root, Node *node)
 	context.max_hazard = PROPARALLEL_SAFE;
 	context.max_interesting = PROPARALLEL_RESTRICTED;
 	context.safe_param_ids = NIL;
+
+	/*
+	 * The params that refer to the same or parent query level are considered
+	 * parallel-safe.  The idea is that we compute such params at Gather or
+	 * Gather Merge node and pass their value to workers.
+	 */
+	for (proot = root; proot != NULL; proot = proot->parent_root)
+	{
+		foreach(l, proot->init_plans)
+		{
+			SubPlan    *initsubplan = (SubPlan *) lfirst(l);
+			ListCell   *l2;
+
+			foreach(l2, initsubplan->setParam)
+				context.safe_param_ids = lcons_int(lfirst_int(l2),
+											context.safe_param_ids);
+		}
+	}
+
 	return !max_parallel_hazard_walker(node, &context);
 }
 
@@ -1224,19 +1245,17 @@ max_parallel_hazard_walker(Node *node, max_parallel_hazard_context *context)
 	/*
 	 * We can't pass Params to workers at the moment either, so they are also
 	 * parallel-restricted, unless they are PARAM_EXEC Params listed in
-	 * safe_param_ids, meaning they could be generated within the worker.
+	 * safe_param_ids, meaning they could be either generated within the
+	 * worker or can be computed in master and then their value can be passed
+	 * to the worker.
 	 */
 	else if (IsA(node, Param))
 	{
-		Param	   *param = (Param *) node;
+		if (list_member_int(context->safe_param_ids, ((Param *) node)->paramid))
+			return false;
 
-		if (param->paramkind != PARAM_EXEC ||
-			!list_member_int(context->safe_param_ids, param->paramid))
-		{
-			if (max_parallel_hazard_test(PROPARALLEL_RESTRICTED, context))
-				return true;
-		}
-		return false;			/* nothing to recurse to */
+		if (max_parallel_hazard_test(PROPARALLEL_RESTRICTED, context))
+			return true;
 	}
 
 	/*
diff --git a/src/include/executor/execExpr.h b/src/include/executor/execExpr.h
index 78d2247..5bbb63a 100644
--- a/src/include/executor/execExpr.h
+++ b/src/include/executor/execExpr.h
@@ -609,6 +609,7 @@ extern ExprEvalOp ExecEvalStepOp(ExprState *state, ExprEvalStep *op);
  */
 extern void ExecEvalParamExec(ExprState *state, ExprEvalStep *op,
 				  ExprContext *econtext);
+extern void ExecEvalParamExecParams(Bitmapset *params, EState *estate);
 extern void ExecEvalParamExtern(ExprState *state, ExprEvalStep *op,
 					ExprContext *econtext);
 extern void ExecEvalSQLValueFunction(ExprState *state, ExprEvalStep *op);
diff --git a/src/include/executor/execParallel.h b/src/include/executor/execParallel.h
index e1b3e7a..88e2757 100644
--- a/src/include/executor/execParallel.h
+++ b/src/include/executor/execParallel.h
@@ -35,7 +35,8 @@ typedef struct ParallelExecutorInfo
 } ParallelExecutorInfo;
 
 extern ParallelExecutorInfo *ExecInitParallelPlan(PlanState *planstate,
-					 EState *estate, int nworkers, int64 tuples_needed);
+					 EState *estate, Bitmapset *initParam, int nworkers,
+					 int64 tuples_needed);
 extern void ExecParallelCreateReaders(ParallelExecutorInfo *pei);
 extern void ExecParallelFinish(ParallelExecutorInfo *pei);
 extern void ExecParallelCleanup(ParallelExecutorInfo *pei);
diff --git a/src/include/executor/nodeSubplan.h b/src/include/executor/nodeSubplan.h
index 5dbaeeb..40b1a34 100644
--- a/src/include/executor/nodeSubplan.h
+++ b/src/include/executor/nodeSubplan.h
@@ -28,4 +28,10 @@ extern void ExecReScanSetParamPlan(SubPlanState *node, PlanState *parent);
 
 extern void ExecSetParamPlan(SubPlanState *node, ExprContext *econtext);
 
+extern Size EstimateInitPlanParamsSpace(ParamExecData *paramExecVals, Bitmapset *params);
+
+extern void SerializeInitPlanParams(ParamExecData *paramExecVals, Bitmapset *params, char **start_address);
+
+extern void RestoreInitPlanParams(char **start_address, ParamExecData *params);
+
 #endif							/* NODESUBPLAN_H */
diff --git a/src/include/nodes/params.h b/src/include/nodes/params.h
index 55219da..e96a1ea 100644
--- a/src/include/nodes/params.h
+++ b/src/include/nodes/params.h
@@ -98,6 +98,16 @@ typedef struct ParamExecData
 {
 	void	   *execPlan;		/* should be "SubPlanState *" */
 	Datum		value;
+
+	/*
+	 * parameter's datatype, or 0.  This is required so that datum value can
+	 * be read and used for other purposes like passing it to worker backend
+	 * via shared memory.  This is required only for initPlan's evaluation,
+	 * however for consistency we set this for Subplan as well.  We left it
+	 * for other cases like CTE or RecursiveUnion cases where this structure
+	 * is not used for evaluation of subplans.
+	 */
+	Oid			ptype;
 	bool		isnull;
 } ParamExecData;
 
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index a382331..a16909c 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -841,6 +841,8 @@ typedef struct Gather
 	int			rescan_param;	/* ID of Param that signals a rescan, or -1 */
 	bool		single_copy;	/* don't execute plan more than once */
 	bool		invisible;		/* suppress EXPLAIN display (for testing)? */
+	Bitmapset  *initParam;		/* param id's of initplans which are referred
+								 * at gather or one of it's child node */
 } Gather;
 
 /* ------------
@@ -858,6 +860,8 @@ typedef struct GatherMerge
 	Oid		   *sortOperators;	/* OIDs of operators to sort them by */
 	Oid		   *collations;		/* OIDs of collations */
 	bool	   *nullsFirst;		/* NULLS FIRST/LAST directions */
+	Bitmapset  *initParam;		/* param id's of initplans which are referred
+								 * at gather merge or one of it's child node */
 } GatherMerge;
 
 /* ----------------
diff --git a/src/test/regress/expected/select_parallel.out b/src/test/regress/expected/select_parallel.out
index 2ae600f..22af824 100644
--- a/src/test/regress/expected/select_parallel.out
+++ b/src/test/regress/expected/select_parallel.out
@@ -139,6 +139,39 @@ explain (costs off)
 (4 rows)
 
 alter table tenk2 reset (parallel_workers);
+--test parallel plan for a query containing initplan.
+set enable_indexscan = off;
+set enable_indexonlyscan = off;
+set enable_bitmapscan = off;
+alter table tenk2 set (parallel_workers = 2);
+explain (costs off)
+	select  count(*) from tenk1 where tenk1.unique1 = (Select max(tenk2.unique1) from tenk2);
+                      QUERY PLAN                      
+------------------------------------------------------
+ Aggregate
+   InitPlan 1 (returns $2)
+     ->  Finalize Aggregate
+           ->  Gather
+                 Workers Planned: 2
+                 ->  Partial Aggregate
+                       ->  Parallel Seq Scan on tenk2
+   ->  Gather
+         Workers Planned: 4
+         Params Evaluated: $2
+         ->  Parallel Seq Scan on tenk1
+               Filter: (unique1 = $2)
+(12 rows)
+
+select  count(*) from tenk1 where tenk1.unique1 = (Select max(tenk2.unique1) from tenk2);
+ count 
+-------
+     1
+(1 row)
+
+reset enable_indexscan;
+reset enable_indexonlyscan;
+reset enable_bitmapscan;
+alter table tenk2 reset (parallel_workers);
 -- test parallel index scans.
 set enable_seqscan to off;
 set enable_bitmapscan to off;
diff --git a/src/test/regress/sql/select_parallel.sql b/src/test/regress/sql/select_parallel.sql
index 89fe80a..ae144ca 100644
--- a/src/test/regress/sql/select_parallel.sql
+++ b/src/test/regress/sql/select_parallel.sql
@@ -52,6 +52,21 @@ explain (costs off)
 	(select ten from tenk2);
 alter table tenk2 reset (parallel_workers);
 
+--test parallel plan for a query containing initplan.
+set enable_indexscan = off;
+set enable_indexonlyscan = off;
+set enable_bitmapscan = off;
+alter table tenk2 set (parallel_workers = 2);
+
+explain (costs off)
+	select  count(*) from tenk1 where tenk1.unique1 = (Select max(tenk2.unique1) from tenk2);
+select  count(*) from tenk1 where tenk1.unique1 = (Select max(tenk2.unique1) from tenk2);
+
+reset enable_indexscan;
+reset enable_indexonlyscan;
+reset enable_bitmapscan;
+alter table tenk2 reset (parallel_workers);
+
 -- test parallel index scans.
 set enable_seqscan to off;
 set enable_bitmapscan to off;