From 605a29661db9f89dfb21692cc6c918a439d14252 Mon Sep 17 00:00:00 2001
From: Tomas Vondra <tomas@2ndquadrant.com>
Date: Fri, 4 Jun 2021 12:59:47 +0200
Subject: [PATCH 3/3] initialize slots only once for batching

---
 src/backend/executor/nodeModifyTable.c | 42 ++++++++++++++------------
 src/include/nodes/execnodes.h          |  1 +
 2 files changed, 24 insertions(+), 19 deletions(-)

diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index c287a371a1..f16c17e8d4 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -678,8 +678,6 @@ ExecInsert(ModifyTableState *mtstate,
 		 */
 		if (resultRelInfo->ri_BatchSize > 1)
 		{
-			TupleDesc tdesc;
-
 			/*
 			 * If a certain number of tuples have already been accumulated, or
 			 * a tuple has come for a different relation than that for the
@@ -705,19 +703,25 @@ ExecInsert(ModifyTableState *mtstate,
 													 resultRelInfo->ri_BatchSize);
 			}
 
-			tdesc = CreateTupleDescCopy(slot->tts_tupleDescriptor);
+			/* initialize the slot, if not already done */
+			if (resultRelInfo->ri_NumSlots >= resultRelInfo->ri_BatchInitialized)
+			{
+				TupleDesc tdesc = CreateTupleDescCopy(slot->tts_tupleDescriptor);
 
-			resultRelInfo->ri_Slots[resultRelInfo->ri_NumSlots] =
-				MakeSingleTupleTableSlot(tdesc,
-										 slot->tts_ops);
-			ExecCopySlot(resultRelInfo->ri_Slots[resultRelInfo->ri_NumSlots],
-						 slot);
+				resultRelInfo->ri_Slots[resultRelInfo->ri_NumSlots] =
+					MakeSingleTupleTableSlot(tdesc,
+											 slot->tts_ops);
+				ExecCopySlot(resultRelInfo->ri_Slots[resultRelInfo->ri_NumSlots],
+							 slot);
 
-			resultRelInfo->ri_PlanSlots[resultRelInfo->ri_NumSlots] =
-				MakeSingleTupleTableSlot(tdesc,
-										 planSlot->tts_ops);
-			ExecCopySlot(resultRelInfo->ri_PlanSlots[resultRelInfo->ri_NumSlots],
-						 planSlot);
+				resultRelInfo->ri_PlanSlots[resultRelInfo->ri_NumSlots] =
+					MakeSingleTupleTableSlot(tdesc,
+											 planSlot->tts_ops);
+				ExecCopySlot(resultRelInfo->ri_PlanSlots[resultRelInfo->ri_NumSlots],
+							 planSlot);
+
+				resultRelInfo->ri_BatchInitialized++;
+			}
 
 			resultRelInfo->ri_NumSlots++;
 
@@ -1039,12 +1043,6 @@ ExecBatchInsert(ModifyTableState *mtstate,
 
 	if (canSetTag && numInserted > 0)
 		estate->es_processed += numInserted;
-
-	for (i = 0; i < numSlots; i++)
-	{
-		ExecDropSingleTupleTableSlot(slots[i]);
-		ExecDropSingleTupleTableSlot(planSlots[i]);
-	}
 }
 
 /* ----------------------------------------------------------------
@@ -3174,6 +3172,12 @@ ExecEndModifyTable(ModifyTableState *node)
 			resultRelInfo->ri_FdwRoutine->EndForeignModify != NULL)
 			resultRelInfo->ri_FdwRoutine->EndForeignModify(node->ps.state,
 														   resultRelInfo);
+
+		for (i = 0; i < resultRelInfo->ri_NumSlots; i++)
+		{
+			ExecDropSingleTupleTableSlot(resultRelInfo->ri_Slots[i]);
+			ExecDropSingleTupleTableSlot(resultRelInfo->ri_PlanSlots[i]);
+		}
 	}
 
 	/*
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 7795a69490..1062a44ee1 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -463,6 +463,7 @@ typedef struct ResultRelInfo
 	/* batch insert stuff */
 	int			ri_NumSlots;	/* number of slots in the array */
 	int			ri_BatchSize;	/* max slots inserted in a single batch */
+	int			ri_BatchInitialized;	/* number of slots initialized */
 	TupleTableSlot **ri_Slots;	/* input tuples for batch insert */
 	TupleTableSlot **ri_PlanSlots;
 
-- 
2.31.1