Allow insert and update tuple routing and COPY for foreign tables.

Also enable this for postgres_fdw.

Etsuro Fujita, based on an earlier patch by Amit Langote. The larger
patch series of which this is a part has been reviewed by Amit
Langote, David Fetter, Maksim Milyutin, Álvaro Herrera, Stephen Frost,
and me.  Minor documentation changes to the final version by me.

Discussion: http://postgr.es/m/29906a26-da12-8c86-4fb9-d8f88442f2b9@lab.ntt.co.jp

src/include/executor/execPartition.h

@@ -119,6 +119,11 @@ extern ResultRelInfo *ExecInitPartitionInfo(ModifyTableState *mtstate,
 					ResultRelInfo *resultRelInfo,
 					PartitionTupleRouting *proute,
 					EState *estate, int partidx);
+extern void ExecInitRoutingInfo(ModifyTableState *mtstate,
+					EState *estate,
+					PartitionTupleRouting *proute,
+					ResultRelInfo *partRelInfo,
+					int partidx);
 extern void ExecSetupChildParentMapForLeaf(PartitionTupleRouting *proute);
 extern TupleConversionMap *TupConvMapForLeaf(PartitionTupleRouting *proute,
 				  ResultRelInfo *rootRelInfo, int leaf_index);
@@ -126,6 +131,7 @@ extern HeapTuple ConvertPartitionTupleSlot(TupleConversionMap *map,
 						  HeapTuple tuple,
 						  TupleTableSlot *new_slot,
 						  TupleTableSlot **p_my_slot);
-extern void ExecCleanupTupleRouting(PartitionTupleRouting *proute);
+extern void ExecCleanupTupleRouting(ModifyTableState *mtstate,
+						PartitionTupleRouting *proute);
 
 #endif							/* EXECPARTITION_H */

src/include/foreign/fdwapi.h

@@ -98,6 +98,12 @@ typedef TupleTableSlot *(*ExecForeignDelete_function) (EState *estate,
 typedef void (*EndForeignModify_function) (EState *estate,
 										   ResultRelInfo *rinfo);
 
+typedef void (*BeginForeignInsert_function) (ModifyTableState *mtstate,
+											 ResultRelInfo *rinfo);
+
+typedef void (*EndForeignInsert_function) (EState *estate,
+										   ResultRelInfo *rinfo);
+
 typedef int (*IsForeignRelUpdatable_function) (Relation rel);
 
 typedef bool (*PlanDirectModify_function) (PlannerInfo *root,
@@ -205,6 +211,8 @@ typedef struct FdwRoutine
 	ExecForeignUpdate_function ExecForeignUpdate;
 	ExecForeignDelete_function ExecForeignDelete;
 	EndForeignModify_function EndForeignModify;
+	BeginForeignInsert_function BeginForeignInsert;
+	EndForeignInsert_function EndForeignInsert;
 	IsForeignRelUpdatable_function IsForeignRelUpdatable;
 	PlanDirectModify_function PlanDirectModify;
 	BeginDirectModify_function BeginDirectModify;

src/include/nodes/execnodes.h

@@ -444,6 +444,9 @@ typedef struct ResultRelInfo
 	/* for removing junk attributes from tuples */
 	JunkFilter *ri_junkFilter;
 
+	/* list of RETURNING expressions */
+	List	   *ri_returningList;
+
 	/* for computing a RETURNING list */
 	ProjectionInfo *ri_projectReturning;
 
@@ -462,6 +465,9 @@ typedef struct ResultRelInfo
 	/* relation descriptor for root partitioned table */
 	Relation	ri_PartitionRoot;
 
+	/* true if ready for tuple routing */
+	bool		ri_PartitionReadyForRouting;
+
 	int			ri_PartitionLeafIndex;
 	/* for running MERGE on this result relation */
 	MergeState *ri_mergeState;