Generalize ri_RootToPartitionMap to use for non-partition children

ri_RootToPartitionMap is currently only initialized for tuple routing
target partitions, though a future commit will need the ability to use
it even for the non-partition child tables, so make adjustments to the
decouple it from the partitioning code.

Also, make it lazily initialized via ExecGetRootToChildMap(), making
that function its preferred access path.  Existing third-party code
accessing it directly should no longer do so; consequently, it's been
renamed to ri_RootToChildMap, which also makes it consistent with
ri_ChildToRootMap.

ExecGetRootToChildMap() houses the logic of setting the map appropriately
depending on whether a given child relation is partition or not.

To support this, also add a separate entry point for TupleConversionMap
creation that receives an AttrMap.  No new code here, just split an
existing function in two.

Author: Amit Langote <amitlangote09@gmail.com>
Discussion: https://postgr.es/m/CA+HiwqEYUhDXSK5BTvG_xk=eaAEJCD4GS3C6uH7ybBvv+Z_Tmg@mail.gmail.com

src/backend/access/common/tupconvert.c

@@ -102,9 +102,7 @@ TupleConversionMap *
 convert_tuples_by_name(TupleDesc indesc,
 					   TupleDesc outdesc)
 {
-	TupleConversionMap *map;
 	AttrMap    *attrMap;
-	int			n = outdesc->natts;
 
 	/* Verify compatibility and prepare attribute-number map */
 	attrMap = build_attrmap_by_name_if_req(indesc, outdesc, false);
@@ -115,6 +113,23 @@ convert_tuples_by_name(TupleDesc indesc,
 		return NULL;
 	}
 
+	return convert_tuples_by_name_attrmap(indesc, outdesc, attrMap);
+}
+
+/*
+ * Set up tuple conversion for input and output TupleDescs using the given
+ * AttrMap.
+ */
+TupleConversionMap *
+convert_tuples_by_name_attrmap(TupleDesc indesc,
+							   TupleDesc outdesc,
+							   AttrMap *attrMap)
+{
+	int			n = outdesc->natts;
+	TupleConversionMap *map;
+
+	Assert(attrMap != NULL);
+
 	/* Prepare the map structure */
 	map = (TupleConversionMap *) palloc(sizeof(TupleConversionMap));
 	map->indesc = indesc;

src/backend/commands/copyfrom.c

@@ -1088,7 +1088,7 @@ CopyFrom(CopyFromState cstate)
 			 * We might need to convert from the root rowtype to the partition
 			 * rowtype.
 			 */
-			map = resultRelInfo->ri_RootToPartitionMap;
+			map = ExecGetRootToChildMap(resultRelInfo, estate);
 			if (insertMethod == CIM_SINGLE || !leafpart_use_multi_insert)
 			{
 				/* non batch insert */

src/backend/executor/execMain.c

@@ -1256,9 +1256,11 @@ InitResultRelInfo(ResultRelInfo *resultRelInfo,
 	 * this field is filled in ExecInitModifyTable().
 	 */
 	resultRelInfo->ri_RootResultRelInfo = partition_root_rri;
-	resultRelInfo->ri_RootToPartitionMap = NULL;	/* set by
-													 * ExecInitRoutingInfo */
-	resultRelInfo->ri_PartitionTupleSlot = NULL;	/* ditto */
+	/* Set by ExecGetRootToChildMap */
+	resultRelInfo->ri_RootToChildMap = NULL;
+	resultRelInfo->ri_RootToChildMapValid = false;
+	/* Set by ExecInitRoutingInfo */
+	resultRelInfo->ri_PartitionTupleSlot = NULL;
 	resultRelInfo->ri_ChildToRootMap = NULL;
 	resultRelInfo->ri_ChildToRootMapValid = false;
 	resultRelInfo->ri_CopyMultiInsertBuffer = NULL;

src/backend/executor/execPartition.c

@@ -463,7 +463,7 @@ ExecFindPartition(ModifyTableState *mtstate,
 			 */
 			if (is_leaf)
 			{
-				TupleConversionMap *map = rri->ri_RootToPartitionMap;
+				TupleConversionMap *map = ExecGetRootToChildMap(rri, estate);
 
 				if (map)
 					slot = execute_attr_map_slot(map->attrMap, rootslot,
@@ -727,7 +727,7 @@ ExecInitPartitionInfo(ModifyTableState *mtstate, EState *estate,
 			OnConflictSetState *onconfl = makeNode(OnConflictSetState);
 			TupleConversionMap *map;
 
-			map = leaf_part_rri->ri_RootToPartitionMap;
+			map = ExecGetRootToChildMap(leaf_part_rri, estate);
 
 			Assert(node->onConflictSet != NIL);
 			Assert(rootResultRelInfo->ri_onConflict != NULL);
@@ -977,33 +977,24 @@ ExecInitRoutingInfo(ModifyTableState *mtstate,
 					int partidx,
 					bool is_borrowed_rel)
 {
-	ResultRelInfo *rootRelInfo = partRelInfo->ri_RootResultRelInfo;
 	MemoryContext oldcxt;
 	int			rri_index;
 
 	oldcxt = MemoryContextSwitchTo(proute->memcxt);
 
 	/*
-	 * Set up a tuple conversion map to convert a tuple routed to the
-	 * partition from the parent's type to the partition's.
+	 * Set up tuple conversion between root parent and the partition if the
+	 * two have different rowtypes.  If conversion is indeed required, also
+	 * initialize a slot dedicated to storing this partition's converted
+	 * tuples.  Various operations that are applied to tuples after routing,
+	 * such as checking constraints, will refer to this slot.
 	 */
-	partRelInfo->ri_RootToPartitionMap =
-		convert_tuples_by_name(RelationGetDescr(rootRelInfo->ri_RelationDesc),
-							   RelationGetDescr(partRelInfo->ri_RelationDesc));
-
-	/*
-	 * If a partition has a different rowtype than the root parent, initialize
-	 * a slot dedicated to storing this partition's tuples.  The slot is used
-	 * for various operations that are applied to tuples after routing, such
-	 * as checking constraints.
-	 */
-	if (partRelInfo->ri_RootToPartitionMap != NULL)
+	if (ExecGetRootToChildMap(partRelInfo, estate) != NULL)
 	{
 		Relation	partrel = partRelInfo->ri_RelationDesc;
 
 		/*
-		 * Initialize the slot itself setting its descriptor to this
-		 * partition's TupleDesc; TupleDesc reference will be released at the
+		 * This pins the partition's TupleDesc, which will be released at the
 		 * end of the command.
 		 */
 		partRelInfo->ri_PartitionTupleSlot =

src/backend/executor/execUtils.c

@@ -1253,6 +1253,45 @@ ExecGetChildToRootMap(ResultRelInfo *resultRelInfo)
 	return resultRelInfo->ri_ChildToRootMap;
 }
 
+/*
+ * Returns the map needed to convert given root result relation's tuples to
+ * the rowtype of the given child relation.  Note that a NULL result is valid
+ * and means that no conversion is needed.
+ */
+TupleConversionMap *
+ExecGetRootToChildMap(ResultRelInfo *resultRelInfo, EState *estate)
+{
+	/* Mustn't get called for a non-child result relation. */
+	Assert(resultRelInfo->ri_RootResultRelInfo);
+
+	/* If we didn't already do so, compute the map for this child. */
+	if (!resultRelInfo->ri_RootToChildMapValid)
+	{
+		ResultRelInfo *rootRelInfo = resultRelInfo->ri_RootResultRelInfo;
+		TupleDesc	indesc = RelationGetDescr(rootRelInfo->ri_RelationDesc);
+		TupleDesc	outdesc = RelationGetDescr(resultRelInfo->ri_RelationDesc);
+		Relation	childrel = resultRelInfo->ri_RelationDesc;
+		AttrMap    *attrMap;
+		MemoryContext oldcontext;
+
+		/*
+		 * When this child table is not a partition (!relispartition), it may
+		 * have columns that are not present in the root table, which we ask
+		 * to ignore by passing true for missing_ok.
+		 */
+		oldcontext = MemoryContextSwitchTo(estate->es_query_cxt);
+		attrMap = build_attrmap_by_name_if_req(indesc, outdesc,
+											   !childrel->rd_rel->relispartition);
+		if (attrMap)
+			resultRelInfo->ri_RootToChildMap =
+				convert_tuples_by_name_attrmap(indesc, outdesc, attrMap);
+		MemoryContextSwitchTo(oldcontext);
+		resultRelInfo->ri_RootToChildMapValid = true;
+	}
+
+	return resultRelInfo->ri_RootToChildMap;
+}
+
 /* Return a bitmap representing columns being inserted */
 Bitmapset *
 ExecGetInsertedCols(ResultRelInfo *relinfo, EState *estate)
@@ -1273,10 +1312,10 @@ ExecGetInsertedCols(ResultRelInfo *relinfo, EState *estate)
 	{
 		ResultRelInfo *rootRelInfo = relinfo->ri_RootResultRelInfo;
 		RangeTblEntry *rte = exec_rt_fetch(rootRelInfo->ri_RangeTableIndex, estate);
+		TupleConversionMap *map = ExecGetRootToChildMap(relinfo, estate);
 
-		if (relinfo->ri_RootToPartitionMap != NULL)
-			return execute_attr_map_cols(relinfo->ri_RootToPartitionMap->attrMap,
-										 rte->insertedCols);
+		if (map != NULL)
+			return execute_attr_map_cols(map->attrMap, rte->insertedCols);
 		else
 			return rte->insertedCols;
 	}
@@ -1307,10 +1346,10 @@ ExecGetUpdatedCols(ResultRelInfo *relinfo, EState *estate)
 	{
 		ResultRelInfo *rootRelInfo = relinfo->ri_RootResultRelInfo;
 		RangeTblEntry *rte = exec_rt_fetch(rootRelInfo->ri_RangeTableIndex, estate);
+		TupleConversionMap *map = ExecGetRootToChildMap(relinfo, estate);
 
-		if (relinfo->ri_RootToPartitionMap != NULL)
-			return execute_attr_map_cols(relinfo->ri_RootToPartitionMap->attrMap,
-										 rte->updatedCols);
+		if (map != NULL)
+			return execute_attr_map_cols(map->attrMap, rte->updatedCols);
 		else
 			return rte->updatedCols;
 	}
@@ -1333,10 +1372,10 @@ ExecGetExtraUpdatedCols(ResultRelInfo *relinfo, EState *estate)
 	{
 		ResultRelInfo *rootRelInfo = relinfo->ri_RootResultRelInfo;
 		RangeTblEntry *rte = exec_rt_fetch(rootRelInfo->ri_RangeTableIndex, estate);
+		TupleConversionMap *map = ExecGetRootToChildMap(relinfo, estate);
 
-		if (relinfo->ri_RootToPartitionMap != NULL)
-			return execute_attr_map_cols(relinfo->ri_RootToPartitionMap->attrMap,
-										 rte->extraUpdatedCols);
+		if (map != NULL)
+			return execute_attr_map_cols(map->attrMap, rte->extraUpdatedCols);
 		else
 			return rte->extraUpdatedCols;
 	}

src/backend/executor/nodeModifyTable.c

@@ -3481,7 +3481,7 @@ ExecPrepareTupleRouting(ModifyTableState *mtstate,
 	/*
 	 * Convert the tuple, if necessary.
 	 */
-	map = partrel->ri_RootToPartitionMap;
+	map = ExecGetRootToChildMap(partrel, estate);
 	if (map != NULL)
 	{
 		TupleTableSlot *new_slot = partrel->ri_PartitionTupleSlot;

src/backend/replication/logical/worker.c

@@ -2193,7 +2193,7 @@ apply_handle_tuple_routing(ApplyExecutionData *edata,
 	remoteslot_part = partrelinfo->ri_PartitionTupleSlot;
 	if (remoteslot_part == NULL)
 		remoteslot_part = table_slot_create(partrel, &estate->es_tupleTable);
-	map = partrelinfo->ri_RootToPartitionMap;
+	map = ExecGetRootToChildMap(partrelinfo, estate);
 	if (map != NULL)
 	{
 		attrmap = map->attrMap;
@@ -2353,7 +2353,7 @@ apply_handle_tuple_routing(ApplyExecutionData *edata,
 					if (remoteslot_part == NULL)
 						remoteslot_part = table_slot_create(partrel_new,
 															&estate->es_tupleTable);
-					map = partrelinfo_new->ri_RootToPartitionMap;
+					map = ExecGetRootToChildMap(partrelinfo_new, estate);
 					if (map != NULL)
 					{
 						remoteslot_part = execute_attr_map_slot(map->attrMap,

src/include/access/tupconvert.h

@@ -39,6 +39,9 @@ extern TupleConversionMap *convert_tuples_by_position(TupleDesc indesc,
 
 extern TupleConversionMap *convert_tuples_by_name(TupleDesc indesc,
 												  TupleDesc outdesc);
+extern TupleConversionMap *convert_tuples_by_name_attrmap(TupleDesc indesc,
+														  TupleDesc outdesc,
+														  AttrMap *attrMap);
 
 extern HeapTuple execute_attr_map_tuple(HeapTuple tuple, TupleConversionMap *map);
 extern TupleTableSlot *execute_attr_map_slot(AttrMap *attrMap,

src/include/executor/executor.h

@@ -600,6 +600,7 @@ extern TupleTableSlot *ExecGetTriggerOldSlot(EState *estate, ResultRelInfo *relI
 extern TupleTableSlot *ExecGetTriggerNewSlot(EState *estate, ResultRelInfo *relInfo);
 extern TupleTableSlot *ExecGetReturningSlot(EState *estate, ResultRelInfo *relInfo);
 extern TupleConversionMap *ExecGetChildToRootMap(ResultRelInfo *resultRelInfo);
+extern TupleConversionMap *ExecGetRootToChildMap(ResultRelInfo *resultRelInfo, EState *estate);
 
 extern Bitmapset *ExecGetInsertedCols(ResultRelInfo *relinfo, EState *estate);
 extern Bitmapset *ExecGetUpdatedCols(ResultRelInfo *relinfo, EState *estate);

src/include/nodes/execnodes.h

@@ -538,22 +538,6 @@ typedef struct ResultRelInfo
 	/* partition check expression state (NULL if not set up yet) */
 	ExprState  *ri_PartitionCheckExpr;
 
-	/*
-	 * Information needed by tuple routing target relations
-	 *
-	 * RootResultRelInfo gives the target relation mentioned in the query, if
-	 * it's a partitioned table. It is not set if the target relation
-	 * mentioned in the query is an inherited table, nor when tuple routing is
-	 * not needed.
-	 *
-	 * RootToPartitionMap and PartitionTupleSlot, initialized by
-	 * ExecInitRoutingInfo, are non-NULL if partition has a different tuple
-	 * format than the root table.
-	 */
-	struct ResultRelInfo *ri_RootResultRelInfo;
-	TupleConversionMap *ri_RootToPartitionMap;
-	TupleTableSlot *ri_PartitionTupleSlot;
-
 	/*
 	 * Map to convert child result relation tuples to the format of the table
 	 * actually mentioned in the query (called "root").  Computed only if
@@ -563,6 +547,26 @@ typedef struct ResultRelInfo
 	TupleConversionMap *ri_ChildToRootMap;
 	bool		ri_ChildToRootMapValid;
 
+	/*
+	 * As above, but in the other direction.
+	 */
+	TupleConversionMap *ri_RootToChildMap;
+	bool		ri_RootToChildMapValid;
+
+	/*
+	 * Information needed by tuple routing target relations
+	 *
+	 * RootResultRelInfo gives the target relation mentioned in the query, if
+	 * it's a partitioned table. It is not set if the target relation
+	 * mentioned in the query is an inherited table, nor when tuple routing is
+	 * not needed.
+	 *
+	 * PartitionTupleSlot is non-NULL if RootToChild conversion is needed and
+	 * the relation is a partition.
+	 */
+	struct ResultRelInfo *ri_RootResultRelInfo;
+	TupleTableSlot *ri_PartitionTupleSlot;
+
 	/* for use by copyfrom.c when performing multi-inserts */
 	struct CopyMultiInsertBuffer *ri_CopyMultiInsertBuffer;