ParallelAppend_v7.patch

diff --git a/src/backend/executor/execParallel.c b/src/backend/executor/execParallel.c
index a1289e5..41d807c 100644
--- a/src/backend/executor/execParallel.c
+++ b/src/backend/executor/execParallel.c
@@ -25,6 +25,7 @@
 
 #include "executor/execParallel.h"
 #include "executor/executor.h"
+#include "executor/nodeAppend.h"
 #include "executor/nodeBitmapHeapscan.h"
 #include "executor/nodeCustom.h"
 #include "executor/nodeForeignscan.h"
@@ -214,6 +215,10 @@ ExecParallelEstimate(PlanState *planstate, ExecParallelEstimateContext *e)
 				ExecForeignScanEstimate((ForeignScanState *) planstate,
 										e->pcxt);
 				break;
+			case T_AppendState:
+				ExecAppendEstimate((AppendState *) planstate,
+										e->pcxt);
+				break;
 			case T_CustomScanState:
 				ExecCustomScanEstimate((CustomScanState *) planstate,
 									   e->pcxt);
@@ -278,6 +283,10 @@ ExecParallelInitializeDSM(PlanState *planstate,
 				ExecForeignScanInitializeDSM((ForeignScanState *) planstate,
 											 d->pcxt);
 				break;
+			case T_AppendState:
+				ExecAppendInitializeDSM((AppendState *) planstate,
+										 d->pcxt);
+				break;
 			case T_CustomScanState:
 				ExecCustomScanInitializeDSM((CustomScanState *) planstate,
 											d->pcxt);
@@ -781,6 +790,9 @@ ExecParallelInitializeWorker(PlanState *planstate, shm_toc *toc)
 				ExecForeignScanInitializeWorker((ForeignScanState *) planstate,
 												toc);
 				break;
+			case T_AppendState:
+				ExecAppendInitializeWorker((AppendState *) planstate, toc);
+				break;
 			case T_CustomScanState:
 				ExecCustomScanInitializeWorker((CustomScanState *) planstate,
 											   toc);
diff --git a/src/backend/executor/nodeAppend.c b/src/backend/executor/nodeAppend.c
index 6986cae..254e5ed 100644
--- a/src/backend/executor/nodeAppend.c
+++ b/src/backend/executor/nodeAppend.c
@@ -59,10 +59,48 @@
 
 #include "executor/execdebug.h"
 #include "executor/nodeAppend.h"
+#include "miscadmin.h"
+#include "optimizer/cost.h"
+#include "storage/spin.h"
 
-static bool exec_append_initialize_next(AppendState *appendstate);
+/*
+ * Shared state for Parallel Append.
+ *
+ * Each backend participating in a Parallel Append has its own
+ * descriptor in backend-private memory, and those objects all contain
+ * a pointer to this structure.
+ */
+typedef struct ParallelAppendDescData
+{
+	slock_t		pa_mutex;		/* mutual exclusion to choose next subplan */
+	int			pa_first_plan;	/* plan to choose while wrapping around plans */
+	int			pa_next_plan;	/* next plan to choose by any worker */
+
+	/*
+	 * pa_finished : workers currently executing the subplan. A worker which
+	 * finishes a subplan should set pa_finished to true, so that no new
+	 * worker picks this subplan. For non-partial subplan, a worker which picks
+	 * up that subplan should immediately set to true, so as to make sure
+	 * there are no more than 1 worker assigned to this subplan.
+	 */
+	bool		pa_finished[FLEXIBLE_ARRAY_MEMBER];
+} ParallelAppendDescData;
+
+typedef ParallelAppendDescData *ParallelAppendDesc;
+
+/*
+ * Special value of AppendState->as_whichplan for Parallel Append, which
+ * indicates there are no plans left to be executed.
+ */
+#define PA_INVALID_PLAN -1
 
 
+static bool exec_append_initialize_next(AppendState *appendstate);
+static void set_finished(ParallelAppendDesc padesc, int whichplan);
+static bool parallel_append_next(AppendState *state);
+static bool leader_next(AppendState *state);
+static int goto_next_plan(int curplan, int first_plan, int last_plan);
+
 /* ----------------------------------------------------------------
  *		exec_append_initialize_next
  *
@@ -77,6 +115,27 @@ exec_append_initialize_next(AppendState *appendstate)
 	int			whichplan;
 
 	/*
+	 * In case it's parallel-aware, follow it's own logic of choosing the next
+	 * subplan.
+	 */
+	if (appendstate->as_padesc)
+	{
+		/* Backward scan is not supported by parallel-aware plans */
+		Assert(ScanDirectionIsForward(appendstate->ps.state->es_direction));
+
+		return parallel_append_next(appendstate);
+	}
+
+	/*
+	 * Not parallel-aware. Fine, just go on to the next subplan in the
+	 * appropriate direction.
+	 */
+	if (ScanDirectionIsForward(appendstate->ps.state->es_direction))
+		appendstate->as_whichplan++;
+	else
+		appendstate->as_whichplan--;
+
+	/*
 	 * get information from the append node
 	 */
 	whichplan = appendstate->as_whichplan;
@@ -176,10 +235,9 @@ ExecInitAppend(Append *node, EState *estate, int eflags)
 	appendstate->ps.ps_ProjInfo = NULL;
 
 	/*
-	 * initialize to scan first subplan
+	 * In case it's a sequential Append, initialize to scan first subplan.
 	 */
 	appendstate->as_whichplan = 0;
-	exec_append_initialize_next(appendstate);
 
 	return appendstate;
 }
@@ -199,6 +257,14 @@ ExecAppend(AppendState *node)
 		TupleTableSlot *result;
 
 		/*
+		 * Check if we are already finished plans from parallel append. This
+		 * can happen if all the subplans are finished when this worker
+		 * has not even started returning tuples.
+		 */
+		if (node->as_padesc && node->as_whichplan == PA_INVALID_PLAN)
+			return ExecClearTuple(node->ps.ps_ResultTupleSlot);
+
+		/*
 		 * figure out which subplan we are currently processing
 		 */
 		subnode = node->appendplans[node->as_whichplan];
@@ -219,14 +285,18 @@ ExecAppend(AppendState *node)
 		}
 
 		/*
-		 * Go on to the "next" subplan in the appropriate direction. If no
-		 * more subplans, return the empty slot set up for us by
-		 * ExecInitAppend.
+		 * We are done with this subplan. There might be other workers still
+		 * processing the last chunk of rows for this same subplan, but there's
+		 * no point for new workers to run this subplan, so mark this subplan
+		 * as finished.
+		 */
+		if (node->as_padesc)
+			set_finished(node->as_padesc, node->as_whichplan);
+
+		/*
+		 * Go on to the "next" subplan. If no more subplans, return the empty
+		 * slot set up for us by ExecInitAppend.
 		 */
-		if (ScanDirectionIsForward(node->ps.state->es_direction))
-			node->as_whichplan++;
-		else
-			node->as_whichplan--;
 		if (!exec_append_initialize_next(node))
 			return ExecClearTuple(node->ps.ps_ResultTupleSlot);
 
@@ -266,6 +336,7 @@ void
 ExecReScanAppend(AppendState *node)
 {
 	int			i;
+	ParallelAppendDesc padesc = node->as_padesc;
 
 	for (i = 0; i < node->as_nplans; i++)
 	{
@@ -285,6 +356,284 @@ ExecReScanAppend(AppendState *node)
 		if (subnode->chgParam == NULL)
 			ExecReScan(subnode);
 	}
+
+	if (padesc)
+	{
+		padesc->pa_first_plan = padesc->pa_next_plan = 0;
+		memset(padesc->pa_finished, 0, sizeof(bool) * node->as_nplans);
+	}
+
 	node->as_whichplan = 0;
-	exec_append_initialize_next(node);
+}
+
+/* ----------------------------------------------------------------
+ *						Parallel Append Support
+ * ----------------------------------------------------------------
+ */
+
+/* ----------------------------------------------------------------
+ *		ExecAppendEstimate
+ *
+ *		estimates the space required to serialize Append node.
+ * ----------------------------------------------------------------
+ */
+void
+ExecAppendEstimate(AppendState *node,
+					ParallelContext *pcxt)
+{
+	node->pappend_len =
+		add_size(offsetof(struct ParallelAppendDescData, pa_finished),
+				 sizeof(bool) * node->as_nplans);
+
+	shm_toc_estimate_chunk(&pcxt->estimator, node->pappend_len);
+	shm_toc_estimate_keys(&pcxt->estimator, 1);
+}
+
+
+/* ----------------------------------------------------------------
+ *		ExecAppendInitializeDSM
+ *
+ *		Set up a Parallel Append descriptor.
+ * ----------------------------------------------------------------
+ */
+void
+ExecAppendInitializeDSM(AppendState *node,
+						 ParallelContext *pcxt)
+{
+	ParallelAppendDesc padesc;
+
+	padesc = shm_toc_allocate(pcxt->toc, node->pappend_len);
+	SpinLockInit(&padesc->pa_mutex);
+
+	/*
+	 * Just setting all the number of workers to 0 is enough. The logic
+	 * of choosing the next plan in workers will take care of everything
+	 * else.
+	 */
+	memset(padesc->pa_finished, 0, sizeof(bool) * node->as_nplans);
+
+	shm_toc_insert(pcxt->toc, node->ps.plan->plan_node_id, padesc);
+	node->as_padesc = padesc;
+
+	/* Choose the optimal subplan to be executed. */
+	(void) parallel_append_next(node);
+}
+
+/* ----------------------------------------------------------------
+ *		ExecAppendInitializeWorker
+ *
+ *		Copy relevant information from TOC into planstate, and initialize
+ *		whatever is required to choose and execute the optimal subplan.
+ * ----------------------------------------------------------------
+ */
+void
+ExecAppendInitializeWorker(AppendState *node, shm_toc *toc)
+{
+	node->as_padesc = shm_toc_lookup(toc, node->ps.plan->plan_node_id);
+
+	/* Choose the optimal subplan to be executed. */
+	(void) parallel_append_next(node);
+}
+
+/* ----------------------------------------------------------------
+ *		set_finished
+ *
+ *		Indicate that this child plan node is about to be finished, so no other
+ *		workers should take up this node. Workers who are already executing
+ *		this node will continue to do so, but workers looking for next nodes to
+ *		pick up would skip this node after this function is called. It is
+ *		possible that multiple workers call this function for the same node at
+ *		the same time, because these workers were executing the same node and
+ *		they finished with it at the same time. The spinlock is not for this
+ *		purpose. The spinlock is used so that it does not change the
+ *		pa_num_workers field while workers are choosing the next node.
+ * ----------------------------------------------------------------
+ */
+static void
+set_finished(ParallelAppendDesc padesc, int whichplan)
+{
+	SpinLockAcquire(&padesc->pa_mutex);
+	padesc->pa_finished[whichplan] = true;
+	SpinLockRelease(&padesc->pa_mutex);
+}
+
+/* ----------------------------------------------------------------
+ *		parallel_append_next
+ *
+ *		Determine the next subplan that should be executed. Each worker uses a
+ *		shared next_subplan counter index to start looking for unfinished plan,
+ *		executes the subplan, then shifts ahead this counter to the next
+ *		subplan, so that other workers know which next plan to choose. This
+ *		way, workers choose the subplans in round robin order, and thus they
+ *		get evenly distributed among the subplans.
+ *
+ *		Returns false if and only if all subplans are already finished
+ *		processing.
+ * ----------------------------------------------------------------
+ */
+static bool
+parallel_append_next(AppendState *state)
+{
+	ParallelAppendDesc padesc = state->as_padesc;
+	int		whichplan;
+	int		initial_plan;
+	int		first_partial_plan = ((Append *)state->ps.plan)->first_partial_plan;
+	bool	found;
+
+	Assert(padesc != NULL);
+
+	/* The parallel leader chooses its next subplan differently */
+	if (!IsParallelWorker())
+		return leader_next(state);
+
+	SpinLockAcquire(&padesc->pa_mutex);
+
+	/* Make a note of which subplan we have started with */
+	initial_plan = padesc->pa_next_plan;
+
+	/*
+	 * Keep going to the next plan until we find an unfinished one. In the
+	 * process, also keep track of the first unfinished non-partial subplan. As
+	 * the non-partial subplans are taken one by one, the first unfinished
+	 * subplan index will shift ahead, so that we don't have to visit the
+	 * finished non-partial ones anymore.
+	 */
+
+	found = false;
+	for (whichplan = initial_plan; whichplan != PA_INVALID_PLAN;)
+	{
+		/*
+		 * Ignore plans that are already done processing. These also include
+		 * non-partial subplans which have already been taken by a worker.
+		 */
+		if (!padesc->pa_finished[whichplan])
+		{
+			found = true;
+			break;
+		}
+
+		/* Either go to the next plan, or wrap around to the first one */
+		whichplan = goto_next_plan(whichplan, padesc->pa_first_plan,
+								   state->as_nplans - 1);
+
+		/*
+		 * If we have wrapped around and returned to the same index again, we
+		 * are done scanning.
+		 */
+		if (whichplan == initial_plan)
+			break;
+	}
+
+	/* If we didn't find any plan to execute, stop executing. */
+	if (!found)
+		padesc->pa_next_plan = state->as_whichplan = PA_INVALID_PLAN;
+	else
+	{
+		/*
+		 * If this a non-partial plan, immediately mark it finished, and shift
+		 * ahead pa_first_plan.
+		 */
+		if (whichplan < first_partial_plan)
+		{
+			padesc->pa_finished[whichplan] = true;
+			padesc->pa_first_plan = whichplan + 1;
+		}
+
+		/*
+		 * Set the chosen plan, and the next plan to be picked by other
+		 * workers.
+		 */
+		state->as_whichplan = whichplan;
+		padesc->pa_next_plan = goto_next_plan(whichplan, padesc->pa_first_plan,
+										   state->as_nplans - 1);
+	}
+
+	SpinLockRelease(&padesc->pa_mutex);
+
+	/*
+	 * Note: There is a chance that just after the child plan node is chosen
+	 * here and spinlock released, some other worker finishes this node and
+	 * calls set_finished(). In that case, this worker will go ahead and call
+	 * ExecProcNode(child_node), which will return NULL tuple since it is
+	 * already finished, and then once again this worker will try to choose
+	 * next subplan; but this is ok : it's just an extra "choose_next_subplan"
+	 * operation.
+	 */
+
+	return found;
+}
+
+/* ----------------------------------------------------------------
+ *		leader_next
+ *
+ *		To be used only if it's a parallel leader. The backend should scan
+ *		backwards from the last plan. This is to prevent it from taking up
+ *		the most expensive non-partial plan, i.e. the first subplan.
+ * ----------------------------------------------------------------
+ */
+static bool
+leader_next(AppendState *state)
+{
+	ParallelAppendDesc padesc = state->as_padesc;
+	int		first_plan;
+	int		whichplan;
+	int		first_partial_plan = ((Append *)state->ps.plan)->first_partial_plan;
+
+	/* The parallel leader should start from the last subplan. */
+
+	SpinLockAcquire(&padesc->pa_mutex);
+	first_plan = padesc->pa_first_plan;
+
+	for (whichplan = state->as_nplans - 1; whichplan >= first_plan;
+		 whichplan--)
+	{
+		if (!padesc->pa_finished[whichplan])
+		{
+			/* If this a non-partial plan, immediately mark it finished */
+			if (whichplan < first_partial_plan)
+				padesc->pa_finished[whichplan] = true;
+
+			break;
+		}
+	}
+
+	SpinLockRelease(&padesc->pa_mutex);
+
+	/* Return false only if we didn't find any plan to execute */
+	if (whichplan < first_plan)
+	{
+		state->as_whichplan = PA_INVALID_PLAN;
+		return false;
+	}
+	else
+	{
+		state->as_whichplan = whichplan;
+		return true;
+	}
+}
+
+/* ----------------------------------------------------------------
+ *		goto_next_plan
+ *
+ *		Either go to the next index, or wrap around to the first unfinished one.
+ * ----------------------------------------------------------------
+ */
+static int goto_next_plan(int curplan, int first_plan, int last_plan)
+{
+	Assert(curplan <= last_plan);
+
+	if (curplan < last_plan)
+		return curplan + 1;
+	else
+	{
+		/*
+		 * We are already at the last plan. If the first_plan itsef is the last
+		 * plan or if it is past the last plan, that means there is no next
+		 * plan remaining. Return Invalid.
+		 */
+		if (first_plan >= last_plan)
+			return PA_INVALID_PLAN;
+
+		return first_plan;
+	}
 }
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 25fd051..7ee0bb8 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -236,6 +236,7 @@ _copyAppend(const Append *from)
 	 * copy remainder of node
 	 */
 	COPY_NODE_FIELD(appendplans);
+	COPY_SCALAR_FIELD(first_partial_plan);
 
 	return newnode;
 }
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 7418fbe..38ade5f 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -369,6 +369,7 @@ _outAppend(StringInfo str, const Append *node)
 	_outPlanInfo(str, (const Plan *) node);
 
 	WRITE_NODE_FIELD(appendplans);
+	WRITE_INT_FIELD(first_partial_plan);
 }
 
 static void
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index d3bbc02..fa1487a 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -1565,6 +1565,7 @@ _readAppend(void)
 	ReadCommonPlan(&local_node->plan);
 
 	READ_NODE_FIELD(appendplans);
+	READ_INT_FIELD(first_partial_plan);
 
 	READ_DONE();
 }
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 43bfd23..094809d 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -99,7 +99,11 @@ static void generate_mergeappend_paths(PlannerInfo *root, RelOptInfo *rel,
 static Path *get_cheapest_parameterized_child_path(PlannerInfo *root,
 									  RelOptInfo *rel,
 									  Relids required_outer);
+static List *paths_insert_sorted_by_cost(List *paths, List *insert_paths);
 static List *accumulate_append_subpath(List *subpaths, Path *path);
+static List *accumulate_partialappend_subpath(List *partial_subpaths,
+								 Path *subpath, bool is_partial,
+								 List **nonpartial_subpaths);
 static void set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
 					  Index rti, RangeTblEntry *rte);
 static void set_function_pathlist(PlannerInfo *root, RelOptInfo *rel,
@@ -1255,6 +1259,7 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
 	List	   *subpaths = NIL;
 	bool		subpaths_valid = true;
 	List	   *partial_subpaths = NIL;
+	List	   *nonpartial_subpaths = NIL;
 	bool		partial_subpaths_valid = true;
 	List	   *all_child_pathkeys = NIL;
 	List	   *all_child_outers = NIL;
@@ -1277,14 +1282,42 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
 		 */
 		if (childrel->cheapest_total_path->param_info == NULL)
 			subpaths = accumulate_append_subpath(subpaths,
-											  childrel->cheapest_total_path);
+												 childrel->cheapest_total_path);
 		else
 			subpaths_valid = false;
 
 		/* Same idea, but for a partial plan. */
 		if (childrel->partial_pathlist != NIL)
-			partial_subpaths = accumulate_append_subpath(partial_subpaths,
-									   linitial(childrel->partial_pathlist));
+			partial_subpaths = accumulate_partialappend_subpath(
+										partial_subpaths,
+										linitial(childrel->partial_pathlist),
+										true, &nonpartial_subpaths);
+		else if (enable_parallelappend)
+		{
+			/*
+			 * Extract the cheapest unparameterized, parallel-safe one among
+			 * the child paths.
+			 */
+			Path *parallel_safe_path =
+				get_cheapest_parallel_safe_total_inner(childrel->pathlist);
+
+			/* If we got one parallel-safe path, add it */
+			if (parallel_safe_path)
+			{
+				partial_subpaths =
+					accumulate_partialappend_subpath(partial_subpaths,
+											  parallel_safe_path, false,
+											  &nonpartial_subpaths);
+			}
+			else
+			{
+				/*
+				 * This child rel neither has a partial path, nor has a
+				 * parallel-safe path. So drop the idea for partial append path.
+				 */
+				partial_subpaths_valid = false;
+			}
+		}
 		else
 			partial_subpaths_valid = false;
 
@@ -1359,7 +1392,8 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
 	 * if we have zero or one live subpath due to constraint exclusion.)
 	 */
 	if (subpaths_valid)
-		add_path(rel, (Path *) create_append_path(rel, subpaths, NULL, 0));
+		add_path(rel, (Path *) create_append_path(rel, subpaths, NIL,
+												  NULL, 0));
 
 	/*
 	 * Consider an append of partial unordered, unparameterized partial paths.
@@ -1367,26 +1401,14 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
 	if (partial_subpaths_valid)
 	{
 		AppendPath *appendpath;
-		ListCell   *lc;
-		int			parallel_workers = 0;
-
-		/*
-		 * Decide on the number of workers to request for this append path.
-		 * For now, we just use the maximum value from among the members.  It
-		 * might be useful to use a higher number if the Append node were
-		 * smart enough to spread out the workers, but it currently isn't.
-		 */
-		foreach(lc, partial_subpaths)
-		{
-			Path	   *path = lfirst(lc);
+		int			parallel_workers;
 
-			parallel_workers = Max(parallel_workers, path->parallel_workers);
-		}
-		Assert(parallel_workers > 0);
+		parallel_workers = get_append_num_workers(partial_subpaths,
+												  nonpartial_subpaths);
 
-		/* Generate a partial append path. */
-		appendpath = create_append_path(rel, partial_subpaths, NULL,
-										parallel_workers);
+		appendpath = create_append_path(rel, nonpartial_subpaths,
+										partial_subpaths,
+										NULL, parallel_workers);
 		add_partial_path(rel, (Path *) appendpath);
 	}
 
@@ -1438,7 +1460,8 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
 
 		if (subpaths_valid)
 			add_path(rel, (Path *)
-					 create_append_path(rel, subpaths, required_outer, 0));
+					 create_append_path(rel, subpaths, NIL,
+										required_outer, 0));
 	}
 }
 
@@ -1652,6 +1675,123 @@ accumulate_append_subpath(List *subpaths, Path *path)
 }
 
 /*
+ * paths_insert_sorted_by_cost
+ *
+ * Insert each of the paths of 'insert_paths' into the right position in
+ * 'paths' so that 'paths' remains sorted by descending order of total cost.
+ *
+ * Return a possibly modified 'paths'.
+ */
+static List *
+paths_insert_sorted_by_cost(List *paths, List *insert_paths)
+{
+	ListCell	   *lci;
+
+	foreach(lci, insert_paths)
+	{
+		Path	   *insert_path = (Path *) lfirst(lci);
+		ListCell	   *lcp;
+		ListCell	   *prev;
+
+		/* Insert this 'insert_path' into 'paths' */
+		prev = NULL;
+		foreach(lcp, paths)
+		{
+			Path	   *path = (Path *) lfirst(lcp);
+
+			/* found the right position ? */
+			if (path->total_cost < insert_path->total_cost)
+				break;
+			prev = lcp;
+		}
+
+		/* Inserting before the first element ? */
+		if (prev == NULL)
+			paths = lcons(insert_path, paths);
+		else
+			(void) lappend_cell(paths, prev, insert_path);
+	}
+
+	return paths;
+}
+
+/*
+ * accumulate_partialappend_subpath:
+ *		Add a subpath to the list being built for a partial Append.
+ *
+ * This is same as accumulate_append_subpath, except that two separate lists
+ * are created, one containing only partial subpaths, and the other containing
+ * only non-partial subpaths. Also, the non-partial paths are kept ordered
+ * by descending total cost.
+ *
+ * is_partial is true if the subpath being added is a partial subpath.
+ */
+static List *
+accumulate_partialappend_subpath(List *partial_subpaths,
+								 Path *subpath, bool is_partial,
+								 List **nonpartial_subpaths)
+{
+	/* list_copy is important here to avoid sharing list substructure */
+
+	if (IsA(subpath, AppendPath))
+	{
+		AppendPath *apath = (AppendPath *) subpath;
+		List	   *apath_partial_paths;
+		List	   *apath_nonpartial_paths;
+
+		/* Split the Append subpaths into partial and non-partial paths */
+		apath_nonpartial_paths = list_truncate(list_copy(apath->subpaths),
+											   apath->first_partial_path);
+		apath_partial_paths = list_copy_tail(apath->subpaths,
+											 apath->first_partial_path);
+
+		/* Add non-partial subpaths, if any. */
+		*nonpartial_subpaths =
+						paths_insert_sorted_by_cost(*nonpartial_subpaths,
+													apath_nonpartial_paths);
+
+		/* Add partial subpaths, if any. */
+		return list_concat(partial_subpaths, apath_partial_paths);
+	}
+	else if (IsA(subpath, MergeAppendPath))
+	{
+		MergeAppendPath *mpath = (MergeAppendPath *) subpath;
+
+		/*
+		 * If at all MergeAppend is partial, all its child plans have to be
+		 * partial : we don't currently support a mix of partial and
+		 * non-partial MergeAppend subpaths.
+		 */
+		if (is_partial)
+			return list_concat(partial_subpaths, list_copy(mpath->subpaths));
+		else
+		{
+			/*
+			 * Since MergePath itself is non-partial, treat all its subpaths
+			 * non-partial.
+			 */
+			*nonpartial_subpaths =
+					paths_insert_sorted_by_cost(*nonpartial_subpaths,
+												mpath->subpaths);
+			return partial_subpaths;
+		}
+	}
+	else
+	{
+		/* Just add it to the right list depending upon whether it's partial */
+		if (is_partial)
+			return lappend(partial_subpaths, subpath);
+		else
+		{
+			*nonpartial_subpaths =
+						paths_insert_sorted_by_cost(*nonpartial_subpaths,
+													list_make1(subpath));
+			return partial_subpaths;
+		}
+	}
+}
+
+/*
  * set_dummy_rel_pathlist
  *	  Build a dummy path for a relation that's been excluded by constraints
  *
@@ -1671,7 +1811,7 @@ set_dummy_rel_pathlist(RelOptInfo *rel)
 	rel->pathlist = NIL;
 	rel->partial_pathlist = NIL;
 
-	add_path(rel, (Path *) create_append_path(rel, NIL, NULL, 0));
+	add_path(rel, (Path *) create_append_path(rel, NIL, NIL, NULL, 0));
 
 	/*
 	 * We set the cheapest path immediately, to ensure that IS_DUMMY_REL()
diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index a129d1e..e8df075 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -127,6 +127,7 @@ bool		enable_material = true;
 bool		enable_mergejoin = true;
 bool		enable_hashjoin = true;
 bool		enable_gathermerge = true;
+bool		enable_parallelappend = true;
 
 typedef struct
 {
@@ -1704,6 +1705,98 @@ cost_sort(Path *path, PlannerInfo *root,
 }
 
 /*
+ * cost_append
+ *	  Determines and returns the cost of an Append node.
+ *
+ * We charge nothing extra for the Append itself, which perhaps is too
+ * optimistic, but since it doesn't do any selection or projection, it is a
+ * pretty cheap node.
+ */
+void
+cost_append(Path *path, List *subpaths, int num_nonpartial_subpaths)
+{
+	ListCell *l;
+
+	path->rows = 0;
+	path->startup_cost = 0;
+	path->total_cost = 0;
+
+	if (path->parallel_aware)
+	{
+		int		parallel_divisor;
+		Cost	highest_nonpartial_cost = 0;
+		int		worker;
+
+		/*
+		 * Make a note of the cost of first non-partial subpath, i.e. the first
+		 * one in the list, if at all there are any non-partial subpaths.
+		 */
+		if (num_nonpartial_subpaths > 0)
+			highest_nonpartial_cost = ((Path *) linitial(subpaths))->total_cost;
+
+		worker = 1;
+		foreach(l, subpaths)
+		{
+			Path	   *subpath = (Path *) lfirst(l);
+
+			/*
+			 * The subpath rows and cost is per worker. We need total count
+			 * of each of the subpaths, so that we can determine the total cost
+			 * of Append. We don't consider non-partial paths separately. The
+			 * parallel_divisor for non-partial paths is 1, and so overall we
+			 * get a good approximation of per-worker cost.
+			 */
+			parallel_divisor = get_parallel_divisor(subpath);
+			path->rows += (subpath->rows * parallel_divisor);
+			path->total_cost += (subpath->total_cost * parallel_divisor);
+
+			/*
+			 * Append would start returning tuples when the child node having
+			 * lowest startup cost is done setting up. We consider only the
+			 * first few subplans that immediately get a worker assigned.
+			 */
+			if (worker <= path->parallel_workers)
+			{
+				path->startup_cost = Min(path->startup_cost,
+										 subpath->startup_cost);
+				worker++;
+			}
+		}
+
+		/* The row count and cost should represent per-worker figures. */
+		parallel_divisor = get_parallel_divisor(path);
+		path->rows = clamp_row_est(path->rows / parallel_divisor);
+		path->total_cost /= parallel_divisor;
+
+		/*
+		 * No matter how fast the partial plans finish, the Append path is
+		 * going to take at least the time needed for the costliest non-partial
+		 * path to finish. This is actually an approximation. We can even
+		 * consider all the other non-partial plans and how workers would get
+		 * scheduled to determine the cost of finishing the non-partial paths.
+		 * But we anyway can't calculate the total cost exactly, especially
+		 * because we can't determine exactly when some of the workers would
+		 * start executing partial plans.
+		 */
+		path->total_cost = Max(highest_nonpartial_cost, path->total_cost);
+	}
+	else
+	{
+		/* Compute rows and costs as sums of subplan rows and costs. */
+		foreach(l, subpaths)
+		{
+			Path	   *subpath = (Path *) lfirst(l);
+
+			path->rows += subpath->rows;
+
+			path->total_cost += subpath->total_cost;
+			if (l == list_head(subpaths))	/* first node? */
+				path->startup_cost = subpath->startup_cost;
+		}
+	}
+}
+
+/*
  * cost_merge_append
  *	  Determines and returns the cost of a MergeAppend node.
  *
diff --git a/src/backend/optimizer/path/joinrels.c b/src/backend/optimizer/path/joinrels.c
index 0551668..401d95a 100644
--- a/src/backend/optimizer/path/joinrels.c
+++ b/src/backend/optimizer/path/joinrels.c
@@ -1217,7 +1217,7 @@ mark_dummy_rel(RelOptInfo *rel)
 	rel->partial_pathlist = NIL;
 
 	/* Set up the dummy path */
-	add_path(rel, (Path *) create_append_path(rel, NIL, NULL, 0));
+	add_path(rel, (Path *) create_append_path(rel, NIL, NIL, NULL, 0));
 
 	/* Set or update cheapest_total_path and related fields */
 	set_cheapest(rel);
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 89e1946..1702015 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -199,7 +199,8 @@ static CteScan *make_ctescan(List *qptlist, List *qpqual,
 			 Index scanrelid, int ctePlanId, int cteParam);
 static WorkTableScan *make_worktablescan(List *qptlist, List *qpqual,
 				   Index scanrelid, int wtParam);
-static Append *make_append(List *appendplans, List *tlist);
+static Append *make_append(List *appendplans, int first_partial_plan,
+						   List *tlist);
 static RecursiveUnion *make_recursive_union(List *tlist,
 					 Plan *lefttree,
 					 Plan *righttree,
@@ -1026,7 +1027,7 @@ create_append_plan(PlannerInfo *root, AppendPath *best_path)
 	 * parent-rel Vars it'll be asked to emit.
 	 */
 
-	plan = make_append(subplans, tlist);
+	plan = make_append(subplans, best_path->first_partial_path, tlist);
 
 	copy_generic_path_info(&plan->plan, (Path *) best_path);
 
@@ -5161,7 +5162,7 @@ make_foreignscan(List *qptlist,
 }
 
 static Append *
-make_append(List *appendplans, List *tlist)
+make_append(List *appendplans, int first_partial_plan, List *tlist)
 {
 	Append	   *node = makeNode(Append);
 	Plan	   *plan = &node->plan;
@@ -5171,6 +5172,7 @@ make_append(List *appendplans, List *tlist)
 	plan->lefttree = NULL;
 	plan->righttree = NULL;
 	node->appendplans = appendplans;
+	node->first_partial_plan = first_partial_plan;
 
 	return node;
 }
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 02286d9..529d91f 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -3345,10 +3345,7 @@ create_grouping_paths(PlannerInfo *root,
 				paths = lappend(paths, path);
 			}
 			path = (Path *)
-				create_append_path(grouped_rel,
-								   paths,
-								   NULL,
-								   0);
+				create_append_path(grouped_rel, paths, NIL, NULL, 0);
 			path->pathtarget = target;
 		}
 		else
diff --git a/src/backend/optimizer/prep/prepunion.c b/src/backend/optimizer/prep/prepunion.c
index 1389db1..e1d70a8 100644
--- a/src/backend/optimizer/prep/prepunion.c
+++ b/src/backend/optimizer/prep/prepunion.c
@@ -566,7 +566,7 @@ generate_union_path(SetOperationStmt *op, PlannerInfo *root,
 	/*
 	 * Append the child results together.
 	 */
-	path = (Path *) create_append_path(result_rel, pathlist, NULL, 0);
+	path = (Path *) create_append_path(result_rel, pathlist, NIL, NULL, 0);
 
 	/* We have to manually jam the right tlist into the path; ick */
 	path->pathtarget = create_pathtarget(root, tlist);
@@ -678,7 +678,7 @@ generate_nonunion_path(SetOperationStmt *op, PlannerInfo *root,
 	/*
 	 * Append the child results together.
 	 */
-	path = (Path *) create_append_path(result_rel, pathlist, NULL, 0);
+	path = (Path *) create_append_path(result_rel, pathlist, NIL, NULL, 0);
 
 	/* We have to manually jam the right tlist into the path; ick */
 	path->pathtarget = create_pathtarget(root, tlist);
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index 8ce772d..6475e23 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -1193,6 +1193,70 @@ create_tidscan_path(PlannerInfo *root, RelOptInfo *rel, List *tidquals,
 }
 
 /*
+ * get_append_num_workers
+ *    Return the number of workers to request for partial append path.
+ */
+int
+get_append_num_workers(List *partial_subpaths, List *nonpartial_subpaths)
+{
+	ListCell   *lc;
+	double		log2w;
+	int			num_workers;
+	int			max_per_plan_workers;
+
+	/*
+	 * log2(number_of_subpaths)+1 formula seems to give an appropriate number of
+	 * workers for Append path either having high number of children (> 100) or
+	 * having all non-partial subpaths or subpaths with 1-2 parallel_workers.
+	 * Whereas, if the subpaths->parallel_workers is high, this formula is not
+	 * suitable, because it does not take into account per-subpath workers.
+	 * For e.g., with workers (2, 8, 8), the Append workers should be at least
+	 * 8, whereas the formula gives 2. In this case, it seems better to follow
+	 * the method used for calculating parallel_workers of an unpartitioned
+	 * table : log3(table_size). So we treat the UNION query as if the data
+	 * belongs to a single unpartitioned table, and then derive its workers. So
+	 * it will be : logb(b^w1 + b^w2 + b^w3) where w1, w2.. are per-subplan
+	 * workers and b is some logarithmic base such as 2 or 3. It turns out that
+	 * this evaluates to a value just a bit greater than max(w1,w2, w3). So, we
+	 * just use the maximum of workers formula. But this formula gives too few
+	 * workers when all paths have single worker (meaning they are non-partial)
+	 * For e.g. with workers : (1, 1, 1, 1, 1, 1), it is better to allocate 3
+	 * workers, whereas this method allocates only 1.
+	 * So we use whichever method that gives higher number of workers.
+	 */
+
+	/* Get log2(num_subpaths) i.e. ln(num_subpaths) / ln(2)  */
+	log2w = log(list_length(partial_subpaths) +
+				list_length(nonpartial_subpaths))
+			/ 0.693 ;
+
+	/* Avoid further calculations if we already crossed max workers limit */
+	if (max_parallel_workers_per_gather <= log2w + 1)
+		return max_parallel_workers_per_gather;
+
+
+	/*
+	 * Get the parallel_workers value of the partial subpath having the highest
+	 * parallel_workers.
+	 */
+	max_per_plan_workers = 1;
+	foreach(lc, partial_subpaths)
+	{
+		Path	   *subpath = lfirst(lc);
+		max_per_plan_workers = Max(max_per_plan_workers,
+								   subpath->parallel_workers);
+	}
+
+	/* Choose the higher of the results of the two formulae */
+	num_workers = rint(Max(log2w, max_per_plan_workers) + 1);
+
+	/* In no case use more than max_parallel_workers_per_gather workers. */
+	num_workers = Min(num_workers, max_parallel_workers_per_gather);
+
+	return num_workers;
+}
+
+/*
  * create_append_path
  *	  Creates a path corresponding to an Append plan, returning the
  *	  pathnode.
@@ -1200,8 +1264,9 @@ create_tidscan_path(PlannerInfo *root, RelOptInfo *rel, List *tidquals,
  * Note that we must handle subpaths = NIL, representing a dummy access path.
  */
 AppendPath *
-create_append_path(RelOptInfo *rel, List *subpaths, Relids required_outer,
-				   int parallel_workers)
+create_append_path(RelOptInfo *rel,
+				   List *subpaths, List *partial_subpaths,
+				   Relids required_outer, int parallel_workers)
 {
 	AppendPath *pathnode = makeNode(AppendPath);
 	ListCell   *l;
@@ -1211,40 +1276,29 @@ create_append_path(RelOptInfo *rel, List *subpaths, Relids required_outer,
 	pathnode->path.pathtarget = rel->reltarget;
 	pathnode->path.param_info = get_appendrel_parampathinfo(rel,
 															required_outer);
-	pathnode->path.parallel_aware = false;
+	pathnode->path.parallel_aware =
+		(enable_parallelappend && parallel_workers > 0);
 	pathnode->path.parallel_safe = rel->consider_parallel;
 	pathnode->path.parallel_workers = parallel_workers;
 	pathnode->path.pathkeys = NIL;		/* result is always considered
 										 * unsorted */
-	pathnode->subpaths = subpaths;
+	pathnode->first_partial_path = list_length(subpaths);
+	pathnode->subpaths = list_concat(subpaths, partial_subpaths);
 
-	/*
-	 * We don't bother with inventing a cost_append(), but just do it here.
-	 *
-	 * Compute rows and costs as sums of subplan rows and costs.  We charge
-	 * nothing extra for the Append itself, which perhaps is too optimistic,
-	 * but since it doesn't do any selection or projection, it is a pretty
-	 * cheap node.
-	 */
-	pathnode->path.rows = 0;
-	pathnode->path.startup_cost = 0;
-	pathnode->path.total_cost = 0;
 	foreach(l, subpaths)
 	{
 		Path	   *subpath = (Path *) lfirst(l);
 
-		pathnode->path.rows += subpath->rows;
-
-		if (l == list_head(subpaths))	/* first node? */
-			pathnode->path.startup_cost = subpath->startup_cost;
-		pathnode->path.total_cost += subpath->total_cost;
 		pathnode->path.parallel_safe = pathnode->path.parallel_safe &&
-			subpath->parallel_safe;
+									   subpath->parallel_safe;
 
 		/* All child paths must have same parameterization */
 		Assert(bms_equal(PATH_REQ_OUTER(subpath), required_outer));
 	}
 
+	cost_append(&pathnode->path, pathnode->subpaths,
+				pathnode->first_partial_path);
+
 	return pathnode;
 }
 
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 4feb26a..4f21c2e 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -911,6 +911,15 @@ static struct config_bool ConfigureNamesBool[] =
 		true,
 		NULL, NULL, NULL
 	},
+	{
+		{"enable_parallelappend", PGC_USERSET, QUERY_TUNING_METHOD,
+			gettext_noop("Enables the planner's use of parallel append plans."),
+			NULL
+		},
+		&enable_parallelappend,
+		true,
+		NULL, NULL, NULL
+	},
 
 	{
 		{"geqo", PGC_USERSET, QUERY_TUNING_GEQO,
diff --git a/src/include/executor/nodeAppend.h b/src/include/executor/nodeAppend.h
index 6fb4662..e76027f 100644
--- a/src/include/executor/nodeAppend.h
+++ b/src/include/executor/nodeAppend.h
@@ -14,11 +14,15 @@
 #ifndef NODEAPPEND_H
 #define NODEAPPEND_H
 
+#include "access/parallel.h"
 #include "nodes/execnodes.h"
 
 extern AppendState *ExecInitAppend(Append *node, EState *estate, int eflags);
 extern TupleTableSlot *ExecAppend(AppendState *node);
 extern void ExecEndAppend(AppendState *node);
 extern void ExecReScanAppend(AppendState *node);
+extern void ExecAppendEstimate(AppendState *node, ParallelContext *pcxt);
+extern void ExecAppendInitializeDSM(AppendState *node, ParallelContext *pcxt);
+extern void ExecAppendInitializeWorker(AppendState *node, shm_toc *toc);
 
 #endif   /* NODEAPPEND_H */
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index f856f60..c822cf2 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -21,6 +21,7 @@
 #include "lib/pairingheap.h"
 #include "nodes/params.h"
 #include "nodes/plannodes.h"
+#include "storage/spin.h"
 #include "utils/hsearch.h"
 #include "utils/reltrigger.h"
 #include "utils/sortsupport.h"
@@ -1187,12 +1188,15 @@ typedef struct ModifyTableState
  *		whichplan		which plan is being executed (0 .. n-1)
  * ----------------
  */
+struct ParallelAppendDescData;
 typedef struct AppendState
 {
 	PlanState	ps;				/* its first field is NodeTag */
 	PlanState **appendplans;	/* array of PlanStates for my inputs */
 	int			as_nplans;
 	int			as_whichplan;
+	struct ParallelAppendDescData *as_padesc; /* parallel coordination info */
+	Size		pappend_len;	/* size of parallel coordination info */
 } AppendState;
 
 /* ----------------
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index b880dc1..79048af 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -228,6 +228,7 @@ typedef struct Append
 {
 	Plan		plan;
 	List	   *appendplans;
+	int			first_partial_plan;
 } Append;
 
 /* ----------------
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h
index 05d6f07..eea8c72 100644
--- a/src/include/nodes/relation.h
+++ b/src/include/nodes/relation.h
@@ -1108,15 +1108,22 @@ typedef struct CustomPath
  * AppendPath represents an Append plan, ie, successive execution of
  * several member plans.
  *
+ * For partial Append, 'subpaths' contains non-partial subpaths followed by
+ * partial subpaths.
+ *
  * Note: it is possible for "subpaths" to contain only one, or even no,
  * elements.  These cases are optimized during create_append_plan.
  * In particular, an AppendPath with no subpaths is a "dummy" path that
  * is created to represent the case that a relation is provably empty.
+ *
  */
 typedef struct AppendPath
 {
 	Path		path;
 	List	   *subpaths;		/* list of component Paths */
+
+	/* Index of first partial path in subpaths */
+	int			first_partial_path;
 } AppendPath;
 
 #define IS_DUMMY_PATH(p) \
diff --git a/src/include/optimizer/cost.h b/src/include/optimizer/cost.h
index d9a9b12..43dc72f 100644
--- a/src/include/optimizer/cost.h
+++ b/src/include/optimizer/cost.h
@@ -67,6 +67,7 @@ extern bool enable_material;
 extern bool enable_mergejoin;
 extern bool enable_hashjoin;
 extern bool enable_gathermerge;
+extern bool enable_parallelappend;
 extern int	constraint_exclusion;
 
 extern double clamp_row_est(double nrows);
@@ -103,6 +104,8 @@ extern void cost_sort(Path *path, PlannerInfo *root,
 		  List *pathkeys, Cost input_cost, double tuples, int width,
 		  Cost comparison_cost, int sort_mem,
 		  double limit_tuples);
+extern void cost_append(Path *path, List *subpaths,
+						int num_nonpartial_subpaths);
 extern void cost_merge_append(Path *path, PlannerInfo *root,
 				  List *pathkeys, int n_streams,
 				  Cost input_startup_cost, Cost input_total_cost,
diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
index 373c722..9622d2f 100644
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -14,6 +14,7 @@
 #ifndef PATHNODE_H
 #define PATHNODE_H
 
+#include "nodes/bitmapset.h"
 #include "nodes/relation.h"
 
 
@@ -63,8 +64,11 @@ extern BitmapOrPath *create_bitmap_or_path(PlannerInfo *root,
 					  List *bitmapquals);
 extern TidPath *create_tidscan_path(PlannerInfo *root, RelOptInfo *rel,
 					List *tidquals, Relids required_outer);
-extern AppendPath *create_append_path(RelOptInfo *rel, List *subpaths,
-				   Relids required_outer, int parallel_workers);
+extern int get_append_num_workers(List *partial_subpaths,
+								  List *nonpartial_subpaths);
+extern AppendPath *create_append_path(RelOptInfo *rel,
+							   List *subpaths, List *partial_subpaths,
+							   Relids required_outer, int parallel_workers);
 extern MergeAppendPath *create_merge_append_path(PlannerInfo *root,
 						 RelOptInfo *rel,
 						 List *subpaths,
diff --git a/src/test/regress/expected/inherit.out b/src/test/regress/expected/inherit.out
index 6494b20..36be3a7 100644
--- a/src/test/regress/expected/inherit.out
+++ b/src/test/regress/expected/inherit.out
@@ -1343,6 +1343,7 @@ select min(1-id) from matest0;
 
 reset enable_indexscan;
 set enable_seqscan = off;  -- plan with fewest seqscans should be merge
+set enable_parallelappend = off; -- Don't let parallel-append interfere
 explain (verbose, costs off) select * from matest0 order by 1-id;
                             QUERY PLAN                            
 ------------------------------------------------------------------
@@ -1409,6 +1410,7 @@ select min(1-id) from matest0;
 (1 row)
 
 reset enable_seqscan;
+reset enable_parallelappend;
 drop table matest0 cascade;
 NOTICE:  drop cascades to 3 other objects
 DETAIL:  drop cascades to table matest1
diff --git a/src/test/regress/expected/select_parallel.out b/src/test/regress/expected/select_parallel.out
index 038a62e..6ffe23d 100644
--- a/src/test/regress/expected/select_parallel.out
+++ b/src/test/regress/expected/select_parallel.out
@@ -11,15 +11,16 @@ set parallel_setup_cost=0;
 set parallel_tuple_cost=0;
 set min_parallel_table_scan_size=0;
 set max_parallel_workers_per_gather=4;
+-- test Parallel Append.
 explain (costs off)
-  select count(*) from a_star;
+  select round(avg(aa)), sum(aa) from a_star;
                      QUERY PLAN                      
 -----------------------------------------------------
  Finalize Aggregate
    ->  Gather
-         Workers Planned: 1
+         Workers Planned: 4
          ->  Partial Aggregate
-               ->  Append
+               ->  Parallel Append
                      ->  Parallel Seq Scan on a_star
                      ->  Parallel Seq Scan on b_star
                      ->  Parallel Seq Scan on c_star
@@ -28,12 +29,40 @@ explain (costs off)
                      ->  Parallel Seq Scan on f_star
 (11 rows)
 
-select count(*) from a_star;
- count 
--------
-    50
+select round(avg(aa)), sum(aa) from a_star;
+ round | sum 
+-------+-----
+    14 | 355
+(1 row)
+
+-- Mix of partial and non-partial subplans.
+alter table c_star set (parallel_workers = 0);
+alter table d_star set (parallel_workers = 0);
+explain (costs off)
+  select round(avg(aa)), sum(aa) from a_star;
+                     QUERY PLAN                      
+-----------------------------------------------------
+ Finalize Aggregate
+   ->  Gather
+         Workers Planned: 4
+         ->  Partial Aggregate
+               ->  Parallel Append
+                     ->  Seq Scan on d_star
+                     ->  Seq Scan on c_star
+                     ->  Parallel Seq Scan on a_star
+                     ->  Parallel Seq Scan on b_star
+                     ->  Parallel Seq Scan on e_star
+                     ->  Parallel Seq Scan on f_star
+(11 rows)
+
+select round(avg(aa)), sum(aa) from a_star;
+ round | sum 
+-------+-----
+    14 | 355
 (1 row)
 
+alter table c_star reset (parallel_workers);
+alter table d_star reset (parallel_workers);
 -- test that parallel_restricted function doesn't run in worker
 alter table tenk1 set (parallel_workers = 4);
 explain (verbose, costs off)
diff --git a/src/test/regress/expected/sysviews.out b/src/test/regress/expected/sysviews.out
index 568b783..97a9843 100644
--- a/src/test/regress/expected/sysviews.out
+++ b/src/test/regress/expected/sysviews.out
@@ -70,21 +70,22 @@ select count(*) >= 0 as ok from pg_prepared_xacts;
 -- This is to record the prevailing planner enable_foo settings during
 -- a regression test run.
 select name, setting from pg_settings where name like 'enable%';
-         name         | setting 
-----------------------+---------
- enable_bitmapscan    | on
- enable_gathermerge   | on
- enable_hashagg       | on
- enable_hashjoin      | on
- enable_indexonlyscan | on
- enable_indexscan     | on
- enable_material      | on
- enable_mergejoin     | on
- enable_nestloop      | on
- enable_seqscan       | on
- enable_sort          | on
- enable_tidscan       | on
-(12 rows)
+         name          | setting 
+-----------------------+---------
+ enable_bitmapscan     | on
+ enable_gathermerge    | on
+ enable_hashagg        | on
+ enable_hashjoin       | on
+ enable_indexonlyscan  | on
+ enable_indexscan      | on
+ enable_material       | on
+ enable_mergejoin      | on
+ enable_nestloop       | on
+ enable_parallelappend | on
+ enable_seqscan        | on
+ enable_sort           | on
+ enable_tidscan        | on
+(13 rows)
 
 -- Test that the pg_timezone_names and pg_timezone_abbrevs views are
 -- more-or-less working.  We can't test their contents in any great detail
diff --git a/src/test/regress/sql/inherit.sql b/src/test/regress/sql/inherit.sql
index e3e9e34..810070a 100644
--- a/src/test/regress/sql/inherit.sql
+++ b/src/test/regress/sql/inherit.sql
@@ -463,11 +463,13 @@ select min(1-id) from matest0;
 reset enable_indexscan;
 
 set enable_seqscan = off;  -- plan with fewest seqscans should be merge
+set enable_parallelappend = off; -- Don't let parallel-append interfere
 explain (verbose, costs off) select * from matest0 order by 1-id;
 select * from matest0 order by 1-id;
 explain (verbose, costs off) select min(1-id) from matest0;
 select min(1-id) from matest0;
 reset enable_seqscan;
+reset enable_parallelappend;
 
 drop table matest0 cascade;
 
diff --git a/src/test/regress/sql/select_parallel.sql b/src/test/regress/sql/select_parallel.sql
index 9311a77..0623319 100644
--- a/src/test/regress/sql/select_parallel.sql
+++ b/src/test/regress/sql/select_parallel.sql
@@ -15,9 +15,18 @@ set parallel_tuple_cost=0;
 set min_parallel_table_scan_size=0;
 set max_parallel_workers_per_gather=4;
 
+-- test Parallel Append.
 explain (costs off)
-  select count(*) from a_star;
-select count(*) from a_star;
+  select round(avg(aa)), sum(aa) from a_star;
+select round(avg(aa)), sum(aa) from a_star;
+-- Mix of partial and non-partial subplans.
+alter table c_star set (parallel_workers = 0);
+alter table d_star set (parallel_workers = 0);
+explain (costs off)
+  select round(avg(aa)), sum(aa) from a_star;
+select round(avg(aa)), sum(aa) from a_star;
+alter table c_star reset (parallel_workers);
+alter table d_star reset (parallel_workers);
 
 -- test that parallel_restricted function doesn't run in worker
 alter table tenk1 set (parallel_workers = 4);