Revise child-to-root tuple conversion map management.

Store the tuple conversion map to convert a tuple from a child table's
format to the root format in a new ri_ChildToRootMap field in
ResultRelInfo. It is initialized if transition tuple capture for FOR
STATEMENT triggers or INSERT tuple routing on a partitioned table is
needed. Previously, ModifyTable kept the maps in the per-subplan
ModifyTableState->mt_per_subplan_tupconv_maps array, or when tuple
routing was used, in
ResultRelInfo->ri_Partitioninfo->pi_PartitionToRootMap. The new field
replaces both of those.

Now that the child-to-root tuple conversion map is always available in
ResultRelInfo (when needed), remove the TransitionCaptureState.tcs_map
field. The callers of Exec*Trigger() functions no longer need to set or
save it, which is much less confusing and bug-prone. Also, as a future
optimization, this will allow us to delay creating the map for a given
result relation until the relation is actually processed during
execution.

Author: Amit Langote
Discussion: https://www.postgresql.org/message-id/CA%2BHiwqHtCWLdK-LO%3DNEsvOdHx%2B7yv4mE_zYK0i3BH7dXb-wxog%40mail.gmail.com

src/backend/commands/copy.c

@@ -3106,31 +3106,14 @@ CopyFrom(CopyState cstate)
 
 			/*
 			 * If we're capturing transition tuples, we might need to convert
-			 * from the partition rowtype to root rowtype.
+			 * from the partition rowtype to root rowtype. But if there are no
+			 * BEFORE triggers on the partition that could change the tuple,
+			 * we can just remember the original unconverted tuple to avoid a
+			 * needless round trip conversion.
 			 */
 			if (cstate->transition_capture != NULL)
-			{
-				if (has_before_insert_row_trig)
-				{
-					/*
-					 * If there are any BEFORE triggers on the partition,
-					 * we'll have to be ready to convert their result back to
-					 * tuplestore format.
-					 */
-					cstate->transition_capture->tcs_original_insert_tuple = NULL;
-					cstate->transition_capture->tcs_map =
-						resultRelInfo->ri_PartitionInfo->pi_PartitionToRootMap;
-				}
-				else
-				{
-					/*
-					 * Otherwise, just remember the original unconverted
-					 * tuple, to avoid a needless round trip conversion.
-					 */
-					cstate->transition_capture->tcs_original_insert_tuple = myslot;
-					cstate->transition_capture->tcs_map = NULL;
-				}
-			}
+				cstate->transition_capture->tcs_original_insert_tuple =
+					!has_before_insert_row_trig ? myslot : NULL;
 
 			/*
 			 * We might need to convert from the root rowtype to the partition

src/backend/commands/trigger.c

@@ -35,6 +35,7 @@
 #include "commands/defrem.h"
 #include "commands/trigger.h"
 #include "executor/executor.h"
+#include "executor/execPartition.h"
 #include "miscadmin.h"
 #include "nodes/bitmapset.h"
 #include "nodes/makefuncs.h"
@@ -4292,9 +4293,10 @@ GetAfterTriggersTableData(Oid relid, CmdType cmdType)
  * If there are no triggers in 'trigdesc' that request relevant transition
  * tables, then return NULL.
  *
- * The resulting object can be passed to the ExecAR* functions.  The caller
- * should set tcs_map or tcs_original_insert_tuple as appropriate when dealing
- * with child tables.
+ * The resulting object can be passed to the ExecAR* functions.  When
+ * dealing with child tables, the caller can set tcs_original_insert_tuple
+ * to avoid having to reconstruct the original tuple in the root table's
+ * format.
  *
  * Note that we copy the flags from a parent table into this struct (rather
  * than subsequently using the relation's TriggerDesc directly) so that we can
@@ -5389,7 +5391,7 @@ AfterTriggerSaveEvent(EState *estate, ResultRelInfo *relinfo,
 	if (row_trigger && transition_capture != NULL)
 	{
 		TupleTableSlot *original_insert_tuple = transition_capture->tcs_original_insert_tuple;
-		TupleConversionMap *map = transition_capture->tcs_map;
+		TupleConversionMap *map = relinfo->ri_ChildToRootMap;
 		bool		delete_old_table = transition_capture->tcs_delete_old_table;
 		bool		update_old_table = transition_capture->tcs_update_old_table;
 		bool		update_new_table = transition_capture->tcs_update_new_table;

src/backend/executor/execMain.c

@@ -1244,6 +1244,7 @@ InitResultRelInfo(ResultRelInfo *resultRelInfo,
 	resultRelInfo->ri_TrigNewSlot = NULL;
 	resultRelInfo->ri_PartitionRoot = partition_root;
 	resultRelInfo->ri_PartitionInfo = NULL; /* may be set later */
+	resultRelInfo->ri_ChildToRootMap = NULL;
 	resultRelInfo->ri_CopyMultiInsertBuffer = NULL;
 }
 

src/backend/executor/execPartition.c

@@ -907,6 +907,15 @@ ExecInitPartitionInfo(ModifyTableState *mtstate, EState *estate,
 		}
 	}
 
+	/*
+	 * Also, if transition capture is required, store a map to convert tuples
+	 * from partition's rowtype to the root partition table's.
+	 */
+	if (mtstate->mt_transition_capture || mtstate->mt_oc_transition_capture)
+		leaf_part_rri->ri_ChildToRootMap =
+			convert_tuples_by_name(RelationGetDescr(leaf_part_rri->ri_RelationDesc),
+								   RelationGetDescr(leaf_part_rri->ri_PartitionRoot));
+
 	/*
 	 * Since we've just initialized this ResultRelInfo, it's not in any list
 	 * attached to the estate as yet.  Add it, so that it can be found later.
@@ -976,20 +985,6 @@ ExecInitRoutingInfo(ModifyTableState *mtstate,
 	else
 		partrouteinfo->pi_PartitionTupleSlot = NULL;
 
-	/*
-	 * Also, if transition capture is required, store a map to convert tuples
-	 * from partition's rowtype to the root partition table's.
-	 */
-	if (mtstate &&
-		(mtstate->mt_transition_capture || mtstate->mt_oc_transition_capture))
-	{
-		partrouteinfo->pi_PartitionToRootMap =
-			convert_tuples_by_name(RelationGetDescr(partRelInfo->ri_RelationDesc),
-								   RelationGetDescr(partRelInfo->ri_PartitionRoot));
-	}
-	else
-		partrouteinfo->pi_PartitionToRootMap = NULL;
-
 	/*
 	 * If the partition is a foreign table, let the FDW init itself for
 	 * routing tuples to the partition.

src/include/commands/trigger.h

@@ -46,7 +46,7 @@ typedef struct TriggerData
  * The state for capturing old and new tuples into transition tables for a
  * single ModifyTable node (or other operation source, e.g. copy.c).
  *
- * This is per-caller to avoid conflicts in setting tcs_map or
+ * This is per-caller to avoid conflicts in setting
  * tcs_original_insert_tuple.  Note, however, that the pointed-to
  * private data may be shared across multiple callers.
  */
@@ -65,14 +65,6 @@ typedef struct TransitionCaptureState
 	bool		tcs_update_new_table;
 	bool		tcs_insert_new_table;
 
-	/*
-	 * For UPDATE and DELETE, AfterTriggerSaveEvent may need to convert the
-	 * new and old tuples from a child table's format to the format of the
-	 * relation named in a query so that it is compatible with the transition
-	 * tuplestores.  The caller must store the conversion map here if so.
-	 */
-	TupleConversionMap *tcs_map;
-
 	/*
 	 * For INSERT and COPY, it would be wasteful to convert tuples from child
 	 * format to parent format after they have already been converted in the

src/include/executor/execPartition.h

@@ -36,12 +36,6 @@ typedef struct PartitionRoutingInfo
 	 */
 	TupleConversionMap *pi_RootToPartitionMap;
 
-	/*
-	 * Map for converting tuples in partition format into the root partitioned
-	 * table format, or NULL if no conversion is required.
-	 */
-	TupleConversionMap *pi_PartitionToRootMap;
-
 	/*
 	 * Slot to store tuples in partition format, or NULL when no translation
 	 * is required between root and partition.

src/include/nodes/execnodes.h

@@ -486,6 +486,13 @@ typedef struct ResultRelInfo
 	/* info for partition tuple routing (NULL if not set up yet) */
 	struct PartitionRoutingInfo *ri_PartitionInfo;
 
+	/*
+	 * Map to convert child result relation tuples to the format of the table
+	 * actually mentioned in the query (called "root").  Set only if
+	 * transition tuple capture or update partition row movement is active.
+	 */
+	TupleConversionMap *ri_ChildToRootMap;
+
 	/* for use by copy.c when performing multi-inserts */
 	struct CopyMultiInsertBuffer *ri_CopyMultiInsertBuffer;
 } ResultRelInfo;
@@ -1179,9 +1186,6 @@ typedef struct ModifyTableState
 
 	/* controls transition table population for INSERT...ON CONFLICT UPDATE */
 	struct TransitionCaptureState *mt_oc_transition_capture;
-
-	/* Per plan map for tuple conversion from child to root */
-	TupleConversionMap **mt_per_subplan_tupconv_maps;
 } ModifyTableState;
 
 /* ----------------