7 files changed, 100 insertions, 0 deletions
diff --git a/src/include/executor/nodeGatherMerge.h b/src/include/executor/nodeGatherMerge.h
new file mode 100644
index 0000000000..3c8b42b6e5
--- /dev/null
+++ b/src/include/executor/nodeGatherMerge.h
@@ -0,0 +1,27 @@
+/*-------------------------------------------------------------------------
+ *
+ * nodeGatherMerge.h
+ *		prototypes for nodeGatherMerge.c
+ *
+ *
+ * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/executor/nodeGatherMerge.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef NODEGATHERMERGE_H
+#define NODEGATHERMERGE_H
+
+#include "nodes/execnodes.h"
+
+extern GatherMergeState *ExecInitGatherMerge(GatherMerge * node,
+					EState *estate,
+					int eflags);
+extern TupleTableSlot *ExecGatherMerge(GatherMergeState * node);
+extern void ExecEndGatherMerge(GatherMergeState * node);
+extern void ExecReScanGatherMerge(GatherMergeState * node);
+extern void ExecShutdownGatherMerge(GatherMergeState * node);
+
+#endif   /* NODEGATHERMERGE_H */
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 6a0d590ef2..f856f6036f 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -2095,6 +2095,35 @@ typedef struct GatherState
 } GatherState;
 
 /* ----------------
+ * GatherMergeState information
+ *
+ *		Gather merge nodes launch 1 or more parallel workers, run a
+ *		subplan which produces sorted output in each worker, and then
+ *		merge the results into a single sorted stream.
+ * ----------------
+ */
+struct GMReaderTuple;
+
+typedef struct GatherMergeState
+{
+	PlanState	ps;				/* its first field is NodeTag */
+	bool		initialized;
+	struct ParallelExecutorInfo *pei;
+	int			nreaders;
+	int			nworkers_launched;
+	struct TupleQueueReader **reader;
+	TupleDesc	tupDesc;
+	TupleTableSlot **gm_slots;
+	struct binaryheap *gm_heap; /* binary heap of slot indices */
+	bool		gm_initialized; /* gather merge initilized ? */
+	bool		need_to_scan_locally;
+	int			gm_nkeys;
+	SortSupport gm_sortkeys;	/* array of length ms_nkeys */
+	struct GMReaderTupleBuffer *gm_tuple_buffers;		/* tuple buffer per
+														 * reader */
+} GatherMergeState;
+
+/* ----------------
  *	 HashState information
  * ----------------
  */
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index 49fa944755..2bc7a5df11 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -77,6 +77,7 @@ typedef enum NodeTag
 	T_WindowAgg,
 	T_Unique,
 	T_Gather,
+	T_GatherMerge,
 	T_Hash,
 	T_SetOp,
 	T_LockRows,
@@ -127,6 +128,7 @@ typedef enum NodeTag
 	T_WindowAggState,
 	T_UniqueState,
 	T_GatherState,
+	T_GatherMergeState,
 	T_HashState,
 	T_SetOpState,
 	T_LockRowsState,
@@ -249,6 +251,7 @@ typedef enum NodeTag
 	T_MaterialPath,
 	T_UniquePath,
 	T_GatherPath,
+	T_GatherMergePath,
 	T_ProjectionPath,
 	T_ProjectSetPath,
 	T_SortPath,
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 7fbb0c2c77..b880dc16cf 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -797,6 +797,22 @@ typedef struct Gather
 	bool		invisible;		/* suppress EXPLAIN display (for testing)? */
 } Gather;
 
+/* ------------
+ *		gather merge node
+ * ------------
+ */
+typedef struct GatherMerge
+{
+	Plan		plan;
+	int			num_workers;
+	/* remaining fields are just like the sort-key info in struct Sort */
+	int			numCols;		/* number of sort-key columns */
+	AttrNumber *sortColIdx;		/* their indexes in the target list */
+	Oid		   *sortOperators;	/* OIDs of operators to sort them by */
+	Oid		   *collations;		/* OIDs of collations */
+	bool	   *nullsFirst;		/* NULLS FIRST/LAST directions */
+} GatherMerge;
+
 /* ----------------
  *		hash build node
  *
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h
index f7ac6f600f..05d6f07aea 100644
--- a/src/include/nodes/relation.h
+++ b/src/include/nodes/relation.h
@@ -1204,6 +1204,19 @@ typedef struct GatherPath
 } GatherPath;
 
 /*
+ * GatherMergePath runs several copies of a plan in parallel and
+ * collects the results. For gather merge parallel leader always execute the
+ * plan.
+ */
+typedef struct GatherMergePath
+{
+	Path		path;
+	Path	   *subpath;		/* path for each worker */
+	int			num_workers;	/* number of workers sought to help */
+} GatherMergePath;
+
+
+/*
  * All join-type paths share these fields.
  */
 
diff --git a/src/include/optimizer/cost.h b/src/include/optimizer/cost.h
index 2b386835e3..d9a9b12a06 100644
--- a/src/include/optimizer/cost.h
+++ b/src/include/optimizer/cost.h
@@ -66,6 +66,7 @@ extern bool enable_nestloop;
 extern bool enable_material;
 extern bool enable_mergejoin;
 extern bool enable_hashjoin;
+extern bool enable_gathermerge;
 extern int	constraint_exclusion;
 
 extern double clamp_row_est(double nrows);
@@ -205,5 +206,9 @@ extern Selectivity clause_selectivity(PlannerInfo *root,
 				   int varRelid,
 				   JoinType jointype,
 				   SpecialJoinInfo *sjinfo);
+extern void cost_gather_merge(GatherMergePath *path, PlannerInfo *root,
+							  RelOptInfo *rel, ParamPathInfo *param_info,
+							  Cost input_startup_cost, Cost input_total_cost,
+							  double *rows);
 
 #endif   /* COST_H */
diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
index f0fe830722..373c7221a8 100644
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -78,6 +78,13 @@ extern UniquePath *create_unique_path(PlannerInfo *root, RelOptInfo *rel,
 extern GatherPath *create_gather_path(PlannerInfo *root,
 				   RelOptInfo *rel, Path *subpath, PathTarget *target,
 				   Relids required_outer, double *rows);
+extern GatherMergePath *create_gather_merge_path(PlannerInfo *root,
+												 RelOptInfo *rel,
+												 Path *subpath,
+												 PathTarget *target,
+												 List *pathkeys,
+												 Relids required_outer,
+												 double *rows);
 extern SubqueryScanPath *create_subqueryscan_path(PlannerInfo *root,
 						 RelOptInfo *rel, Path *subpath,
 						 List *pathkeys, Relids required_outer);