From f06fb5acfbf8e934965ea6083b432e0f7aecfd01 Mon Sep 17 00:00:00 2001
From: HuaiyuXu <391585975@qq.com>
Date: Wed, 30 Nov 2022 19:28:01 +0800
Subject: [PATCH] util, executor: refine the memory usage of delete multiple
 tables (#39489)

close pingcap/tidb#35886
---
 executor/delete.go | 17 ++++++++++++-----
 util/chunk/row.go  | 20 +++++++++++++++-----
 2 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/executor/delete.go b/executor/delete.go
index 9e64a47669f9f..3aa0932a07c22 100644
--- a/executor/delete.go
+++ b/executor/delete.go
@@ -175,8 +175,14 @@ func (e *DeleteExec) composeTblRowMap(tblRowMap tableRowMapType, colPosInfos []p
 			return err
 		}
 		// tblRowMap[info.TblID][handle] hold the row datas binding to this table and this handle.
-		_, exist := tblRowMap[info.TblID].Get(handle)
-		memDelta := tblRowMap[info.TblID].Set(handle, joinedRow[info.Start:info.End])
+		row, exist := tblRowMap[info.TblID].Get(handle)
+		if !exist {
+			row = make([]types.Datum, info.End-info.Start)
+		}
+		for i, d := range joinedRow[info.Start:info.End] {
+			d.Copy(&row[i])
+		}
+		memDelta := tblRowMap[info.TblID].Set(handle, row)
 		if !exist {
 			memDelta += types.EstimatedMemUsage(joinedRow, 1)
 			memDelta += int64(handle.ExtraMemSize())
@@ -192,6 +198,7 @@ func (e *DeleteExec) deleteMultiTablesByChunk(ctx context.Context) error {
 	fields := retTypes(e.children[0])
 	chk := tryNewCacheChunk(e.children[0])
 	memUsageOfChk := int64(0)
+	joinedDatumRowBuffer := make([]types.Datum, len(fields))
 	for {
 		e.memTracker.Consume(-memUsageOfChk)
 		iter := chunk.NewIterator4Chunk(chk)
@@ -206,13 +213,13 @@ func (e *DeleteExec) deleteMultiTablesByChunk(ctx context.Context) error {
 		e.memTracker.Consume(memUsageOfChk)
 
 		for joinedChunkRow := iter.Begin(); joinedChunkRow != iter.End(); joinedChunkRow = iter.Next() {
-			joinedDatumRow := joinedChunkRow.GetDatumRow(fields)
-			err := e.composeTblRowMap(tblRowMap, colPosInfos, joinedDatumRow)
+			joinedDatumRowBuffer = joinedChunkRow.GetDatumRowWithBuffer(fields, joinedDatumRowBuffer)
+			err := e.composeTblRowMap(tblRowMap, colPosInfos, joinedDatumRowBuffer)
 			if err != nil {
 				return err
 			}
 		}
-		chk = chunk.Renew(chk, e.maxChunkSize)
+		chk = tryNewCacheChunk(e.children[0])
 	}
 
 	return e.removeRowsInTblRowMap(tblRowMap)
diff --git a/util/chunk/row.go b/util/chunk/row.go
index 96aa92acb65fb..04aba8f768bdd 100644
--- a/util/chunk/row.go
+++ b/util/chunk/row.go
@@ -115,10 +115,14 @@ func (r Row) GetJSON(colIdx int) types.BinaryJSON {
 // Keep in mind that GetDatumRow has a reference to r.c, which is a chunk,
 // this function works only if the underlying chunk is valid or unchanged.
 func (r Row) GetDatumRow(fields []*types.FieldType) []types.Datum {
-	datumRow := make([]types.Datum, 0, r.c.NumCols())
-	for colIdx := 0; colIdx < r.c.NumCols(); colIdx++ {
-		datum := r.GetDatum(colIdx, fields[colIdx])
-		datumRow = append(datumRow, datum)
+	datumRow := make([]types.Datum, r.c.NumCols())
+	return r.GetDatumRowWithBuffer(fields, datumRow)
+}
+
+// GetDatumRowWithBuffer gets datum using the buffer datumRow.
+func (r Row) GetDatumRowWithBuffer(fields []*types.FieldType, datumRow []types.Datum) []types.Datum {
+	for colIdx := 0; colIdx < len(datumRow); colIdx++ {
+		r.GetDatumWithBuffer(colIdx, fields[colIdx], &datumRow[colIdx])
 	}
 	return datumRow
 }
@@ -126,6 +130,12 @@ func (r Row) GetDatumRow(fields []*types.FieldType) []types.Datum {
 // GetDatum implements the chunk.Row interface.
 func (r Row) GetDatum(colIdx int, tp *types.FieldType) types.Datum {
 	var d types.Datum
+	r.GetDatumWithBuffer(colIdx, tp, &d)
+	return d
+}
+
+// GetDatumWithBuffer gets datum using the buffer d.
+func (r Row) GetDatumWithBuffer(colIdx int, tp *types.FieldType, d *types.Datum) types.Datum {
 	switch tp.GetType() {
 	case mysql.TypeTiny, mysql.TypeShort, mysql.TypeInt24, mysql.TypeLong, mysql.TypeLonglong:
 		if !r.IsNull(colIdx) {
@@ -192,7 +202,7 @@ func (r Row) GetDatum(colIdx int, tp *types.FieldType) types.Datum {
 			d.SetMysqlJSON(r.GetJSON(colIdx))
 		}
 	}
-	return d
+	return *d
 }
 
 // GetRaw returns the underlying raw bytes with the colIdx.