Use ResultRelInfo ** rather than ResultRelInfo * for tuple routing.

The previous convention doesn't lend itself to creating ResultRelInfos
lazily, as we already do in ExecGetTriggerResultRel.  This patch
doesn't make anything lazier than before, but the pending patch for
UPDATE tuple routing proposes to do so (and there might be other
opportunities as well).

Amit Khandekar with some adjustments by me.

Discussion: http://postgr.es/m/CA+TgmoYPVP9Lyf6vUFA5DwxS4c--x6LOj2y36BsJaYtp62eXPQ@mail.gmail.com

src/backend/commands/copy.c

@@ -167,7 +167,7 @@ typedef struct CopyStateData
 	PartitionDispatch *partition_dispatch_info;
 	int			num_dispatch;	/* Number of entries in the above array */
 	int			num_partitions; /* Number of members in the following arrays */
-	ResultRelInfo *partitions;	/* Per partition result relation */
+	ResultRelInfo **partitions;	/* Per partition result relation pointers */
 	TupleConversionMap **partition_tupconv_maps;
 	TupleTableSlot *partition_tuple_slot;
 	TransitionCaptureState *transition_capture;
@@ -2459,7 +2459,7 @@ CopyFrom(CopyState cstate)
 	if (cstate->rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
 	{
 		PartitionDispatch *partition_dispatch_info;
-		ResultRelInfo *partitions;
+		ResultRelInfo **partitions;
 		TupleConversionMap **partition_tupconv_maps;
 		TupleTableSlot *partition_tuple_slot;
 		int			num_parted,
@@ -2495,7 +2495,7 @@ CopyFrom(CopyState cstate)
 			for (i = 0; i < cstate->num_partitions; ++i)
 			{
 				cstate->transition_tupconv_maps[i] =
-					convert_tuples_by_name(RelationGetDescr(cstate->partitions[i].ri_RelationDesc),
+					convert_tuples_by_name(RelationGetDescr(cstate->partitions[i]->ri_RelationDesc),
 										   RelationGetDescr(cstate->rel),
 										   gettext_noop("could not convert row type"));
 			}
@@ -2626,7 +2626,7 @@ CopyFrom(CopyState cstate)
 			 * to the selected partition.
 			 */
 			saved_resultRelInfo = resultRelInfo;
-			resultRelInfo = cstate->partitions + leaf_part_index;
+			resultRelInfo = cstate->partitions[leaf_part_index];
 
 			/* We do not yet have a way to insert into a foreign partition */
 			if (resultRelInfo->ri_FdwRoutine)
@@ -2856,7 +2856,7 @@ CopyFrom(CopyState cstate)
 		}
 		for (i = 0; i < cstate->num_partitions; i++)
 		{
-			ResultRelInfo *resultRelInfo = cstate->partitions + i;
+			ResultRelInfo *resultRelInfo = cstate->partitions[i];
 
 			ExecCloseIndices(resultRelInfo);
 			heap_close(resultRelInfo->ri_RelationDesc, NoLock);

src/backend/executor/execMain.c

@@ -3242,7 +3242,7 @@ EvalPlanQualEnd(EPQState *epqstate)
  * Output arguments:
  * 'pd' receives an array of PartitionDispatch objects with one entry for
  *		every partitioned table in the partition tree
- * 'partitions' receives an array of ResultRelInfo objects with one entry for
+ * 'partitions' receives an array of ResultRelInfo* objects with one entry for
  *		every leaf partition in the partition tree
  * 'tup_conv_maps' receives an array of TupleConversionMap objects with one
  *		entry for every leaf partition (required to convert input tuple based
@@ -3265,7 +3265,7 @@ ExecSetupPartitionTupleRouting(Relation rel,
 							   Index resultRTindex,
 							   EState *estate,
 							   PartitionDispatch **pd,
-							   ResultRelInfo **partitions,
+							   ResultRelInfo ***partitions,
 							   TupleConversionMap ***tup_conv_maps,
 							   TupleTableSlot **partition_tuple_slot,
 							   int *num_parted, int *num_partitions)
@@ -3283,8 +3283,8 @@ ExecSetupPartitionTupleRouting(Relation rel,
 	(void) find_all_inheritors(RelationGetRelid(rel), RowExclusiveLock, NULL);
 	*pd = RelationGetPartitionDispatchInfo(rel, num_parted, &leaf_parts);
 	*num_partitions = list_length(leaf_parts);
-	*partitions = (ResultRelInfo *) palloc(*num_partitions *
-										   sizeof(ResultRelInfo));
+	*partitions = (ResultRelInfo **) palloc(*num_partitions *
+											sizeof(ResultRelInfo *));
 	*tup_conv_maps = (TupleConversionMap **) palloc0(*num_partitions *
 													 sizeof(TupleConversionMap *));
 
@@ -3296,7 +3296,8 @@ ExecSetupPartitionTupleRouting(Relation rel,
 	 */
 	*partition_tuple_slot = MakeTupleTableSlot();
 
-	leaf_part_rri = *partitions;
+	leaf_part_rri = (ResultRelInfo *) palloc0(*num_partitions *
+											  sizeof(ResultRelInfo));
 	i = 0;
 	foreach(cell, leaf_parts)
 	{
@@ -3341,7 +3342,7 @@ ExecSetupPartitionTupleRouting(Relation rel,
 		estate->es_leaf_result_relations =
 			lappend(estate->es_leaf_result_relations, leaf_part_rri);
 
-		leaf_part_rri++;
+		(*partitions)[i] = leaf_part_rri++;
 		i++;
 	}
 }

src/backend/executor/nodeModifyTable.c

@@ -303,7 +303,7 @@ ExecInsert(ModifyTableState *mtstate,
 		 * the selected partition.
 		 */
 		saved_resultRelInfo = resultRelInfo;
-		resultRelInfo = mtstate->mt_partitions + leaf_part_index;
+		resultRelInfo = mtstate->mt_partitions[leaf_part_index];
 
 		/* We do not yet have a way to insert into a foreign partition */
 		if (resultRelInfo->ri_FdwRoutine)
@@ -1498,25 +1498,11 @@ ExecSetupTransitionCaptureState(ModifyTableState *mtstate, EState *estate)
 	if (mtstate->mt_transition_capture != NULL ||
 		mtstate->mt_oc_transition_capture != NULL)
 	{
-		ResultRelInfo *resultRelInfos;
 		int			numResultRelInfos;
 
-		/* Find the set of partitions so that we can find their TupleDescs. */
-		if (mtstate->mt_partition_dispatch_info != NULL)
-		{
-			/*
-			 * For INSERT via partitioned table, so we need TupleDescs based
-			 * on the partition routing table.
-			 */
-			resultRelInfos = mtstate->mt_partitions;
-			numResultRelInfos = mtstate->mt_num_partitions;
-		}
-		else
-		{
-			/* Otherwise we need the ResultRelInfo for each subplan. */
-			resultRelInfos = mtstate->resultRelInfo;
-			numResultRelInfos = mtstate->mt_nplans;
-		}
+		numResultRelInfos = (mtstate->mt_partition_tuple_slot != NULL ?
+							 mtstate->mt_num_partitions :
+							 mtstate->mt_nplans);
 
 		/*
 		 * Build array of conversion maps from each child's TupleDesc to the
@@ -1526,12 +1512,36 @@ ExecSetupTransitionCaptureState(ModifyTableState *mtstate, EState *estate)
 		 */
 		mtstate->mt_transition_tupconv_maps = (TupleConversionMap **)
 			palloc0(sizeof(TupleConversionMap *) * numResultRelInfos);
-		for (i = 0; i < numResultRelInfos; ++i)
+
+		/* Choose the right set of partitions */
+		if (mtstate->mt_partition_dispatch_info != NULL)
 		{
-			mtstate->mt_transition_tupconv_maps[i] =
-				convert_tuples_by_name(RelationGetDescr(resultRelInfos[i].ri_RelationDesc),
-									   RelationGetDescr(targetRelInfo->ri_RelationDesc),
-									   gettext_noop("could not convert row type"));
+			/*
+			 * For tuple routing among partitions, we need TupleDescs based
+			 * on the partition routing table.
+			 */
+			ResultRelInfo **resultRelInfos = mtstate->mt_partitions;
+
+			for (i = 0; i < numResultRelInfos; ++i)
+			{
+				mtstate->mt_transition_tupconv_maps[i] =
+					convert_tuples_by_name(RelationGetDescr(resultRelInfos[i]->ri_RelationDesc),
+										   RelationGetDescr(targetRelInfo->ri_RelationDesc),
+										   gettext_noop("could not convert row type"));
+			}
+		}
+		else
+		{
+			/* Otherwise we need the ResultRelInfo for each subplan. */
+			ResultRelInfo *resultRelInfos = mtstate->resultRelInfo;
+
+			for (i = 0; i < numResultRelInfos; ++i)
+			{
+				mtstate->mt_transition_tupconv_maps[i] =
+					convert_tuples_by_name(RelationGetDescr(resultRelInfos[i].ri_RelationDesc),
+										   RelationGetDescr(targetRelInfo->ri_RelationDesc),
+										   gettext_noop("could not convert row type"));
+			}
 		}
 
 		/*
@@ -1935,7 +1945,7 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 		rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
 	{
 		PartitionDispatch *partition_dispatch_info;
-		ResultRelInfo *partitions;
+		ResultRelInfo **partitions;
 		TupleConversionMap **partition_tupconv_maps;
 		TupleTableSlot *partition_tuple_slot;
 		int			num_parted,
@@ -2014,14 +2024,16 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 			   mtstate->mt_nplans == 1);
 		wcoList = linitial(node->withCheckOptionLists);
 		plan = mtstate->mt_plans[0];
-		resultRelInfo = mtstate->mt_partitions;
 		for (i = 0; i < mtstate->mt_num_partitions; i++)
 		{
-			Relation	partrel = resultRelInfo->ri_RelationDesc;
+			Relation	partrel;
 			List	   *mapped_wcoList;
 			List	   *wcoExprs = NIL;
 			ListCell   *ll;
 
+			resultRelInfo = mtstate->mt_partitions[i];
+			partrel = resultRelInfo->ri_RelationDesc;
+
 			/* varno = node->nominalRelation */
 			mapped_wcoList = map_partition_varattnos(wcoList,
 													 node->nominalRelation,
@@ -2037,7 +2049,6 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 
 			resultRelInfo->ri_WithCheckOptions = mapped_wcoList;
 			resultRelInfo->ri_WithCheckOptionExprs = wcoExprs;
-			resultRelInfo++;
 		}
 	}
 
@@ -2088,13 +2099,15 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 		 * will suffice.  This only occurs for the INSERT case; UPDATE/DELETE
 		 * are handled above.
 		 */
-		resultRelInfo = mtstate->mt_partitions;
 		returningList = linitial(node->returningLists);
 		for (i = 0; i < mtstate->mt_num_partitions; i++)
 		{
-			Relation	partrel = resultRelInfo->ri_RelationDesc;
+			Relation	partrel;
 			List	   *rlist;
 
+			resultRelInfo = mtstate->mt_partitions[i];
+			partrel = resultRelInfo->ri_RelationDesc;
+
 			/* varno = node->nominalRelation */
 			rlist = map_partition_varattnos(returningList,
 											node->nominalRelation,
@@ -2102,7 +2115,6 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 			resultRelInfo->ri_projectReturning =
 				ExecBuildProjectionInfo(rlist, econtext, slot, &mtstate->ps,
 										resultRelInfo->ri_RelationDesc->rd_att);
-			resultRelInfo++;
 		}
 	}
 	else
@@ -2376,7 +2388,7 @@ ExecEndModifyTable(ModifyTableState *node)
 	}
 	for (i = 0; i < node->mt_num_partitions; i++)
 	{
-		ResultRelInfo *resultRelInfo = node->mt_partitions + i;
+		ResultRelInfo *resultRelInfo = node->mt_partitions[i];
 
 		ExecCloseIndices(resultRelInfo);
 		heap_close(resultRelInfo->ri_RelationDesc, NoLock);

src/include/executor/executor.h

@@ -210,7 +210,7 @@ extern void ExecSetupPartitionTupleRouting(Relation rel,
 							   Index resultRTindex,
 							   EState *estate,
 							   PartitionDispatch **pd,
-							   ResultRelInfo **partitions,
+							   ResultRelInfo ***partitions,
 							   TupleConversionMap ***tup_conv_maps,
 							   TupleTableSlot **partition_tuple_slot,
 							   int *num_parted, int *num_partitions);

src/include/nodes/execnodes.h

@@ -979,7 +979,7 @@ typedef struct ModifyTableState
 	int			mt_num_dispatch;	/* Number of entries in the above array */
 	int			mt_num_partitions;	/* Number of members in the following
 									 * arrays */
-	ResultRelInfo *mt_partitions;	/* Per partition result relation */
+	ResultRelInfo **mt_partitions;	/* Per partition result relation pointers */
 	TupleConversionMap **mt_partition_tupconv_maps;
 	/* Per partition tuple conversion map */
 	TupleTableSlot *mt_partition_tuple_slot;