diff --git a/br/pkg/lightning/verification/checksum.go b/br/pkg/lightning/verification/checksum.go
index 45d60b52c2e88..d30e143b301ad 100644
--- a/br/pkg/lightning/verification/checksum.go
+++ b/br/pkg/lightning/verification/checksum.go
@@ -35,11 +35,9 @@ type KVChecksum struct {
 	checksum  uint64
 }
 
-// NewKVChecksum creates a new KVChecksum with the given checksum.
-func NewKVChecksum(checksum uint64) *KVChecksum {
-	return &KVChecksum{
-		checksum: checksum,
-	}
+// NewKVChecksum creates a pointer to zero KVChecksum.
+func NewKVChecksum() *KVChecksum {
+	return &KVChecksum{}
 }
 
 // NewKVChecksumWithKeyspace creates a new KVChecksum with the given checksum and keyspace.
@@ -135,29 +133,30 @@ type KVGroupChecksum struct {
 	codec tikv.Codec
 }
 
-// DataKVGroupAsIndexID represents the index ID for data KV group.
-const DataKVGroupAsIndexID = -1
+// DataKVGroupID represents the ID for data KV group, as index id starts from 1,
+// so we use -1 to represent data kv group.
+const DataKVGroupID = -1
 
 // NewKVGroupChecksumWithKeyspace creates a new KVGroupChecksum with the given
 // keyspace.
 func NewKVGroupChecksumWithKeyspace(k tikv.Codec) *KVGroupChecksum {
 	m := make(map[int64]*KVChecksum, 8)
-	m[DataKVGroupAsIndexID] = NewKVChecksumWithKeyspace(k)
+	m[DataKVGroupID] = NewKVChecksumWithKeyspace(k)
 	return &KVGroupChecksum{m: m, codec: k}
 }
 
-// NewKVGroupChecksumForAdd creates a new KVGroupChecksum and it can't be used
+// NewKVGroupChecksumForAdd creates a new KVGroupChecksum, and it can't be used
 // with UpdateOneDataKV or UpdateOneIndexKV.
 func NewKVGroupChecksumForAdd() *KVGroupChecksum {
 	m := make(map[int64]*KVChecksum, 8)
-	m[DataKVGroupAsIndexID] = NewKVChecksum(0)
+	m[DataKVGroupID] = NewKVChecksum()
 	return &KVGroupChecksum{m: m}
 }
 
 // UpdateOneDataKV updates the checksum with a single data(record) key-value
 // pair. It will not check the key-value pair's key is a real data key again.
 func (c *KVGroupChecksum) UpdateOneDataKV(kv common.KvPair) {
-	c.m[DataKVGroupAsIndexID].UpdateOne(kv)
+	c.m[DataKVGroupID].UpdateOne(kv)
 }
 
 // UpdateOneIndexKV updates the checksum with a single index key-value pair. It
@@ -175,30 +174,28 @@ func (c *KVGroupChecksum) UpdateOneIndexKV(indexID int64, kv common.KvPair) {
 // Add adds the checksum of another KVGroupChecksum.
 func (c *KVGroupChecksum) Add(other *KVGroupChecksum) {
 	for id, cksum := range other.m {
-		thisCksum := c.m[id]
-		if thisCksum == nil {
-			if c.codec == nil {
-				thisCksum = NewKVChecksum(0)
-			} else {
-				thisCksum = NewKVChecksumWithKeyspace(c.codec)
-			}
-			c.m[id] = thisCksum
-		}
+		thisCksum := c.getOrCreateOneGroup(id)
 		thisCksum.Add(cksum)
 	}
 }
 
+func (c *KVGroupChecksum) getOrCreateOneGroup(id int64) *KVChecksum {
+	cksum, ok := c.m[id]
+	if ok {
+		return cksum
+	}
+	if c.codec == nil {
+		cksum = NewKVChecksum()
+	} else {
+		cksum = NewKVChecksumWithKeyspace(c.codec)
+	}
+	c.m[id] = cksum
+	return cksum
+}
+
 // AddRawGroup adds the raw information of a KV group.
 func (c *KVGroupChecksum) AddRawGroup(id int64, bytes, kvs, checksum uint64) {
-	oneGroup, ok := c.m[id]
-	if !ok {
-		if c.codec == nil {
-			oneGroup = NewKVChecksum(0)
-		} else {
-			oneGroup = NewKVChecksumWithKeyspace(c.codec)
-		}
-		c.m[id] = oneGroup
-	}
+	oneGroup := c.getOrCreateOneGroup(id)
 	tmp := MakeKVChecksum(bytes, kvs, checksum)
 	oneGroup.Add(&tmp)
 }
@@ -206,7 +203,7 @@ func (c *KVGroupChecksum) AddRawGroup(id int64, bytes, kvs, checksum uint64) {
 // DataAndIndexSumSize returns the total size of data KV pairs and index KV pairs.
 func (c *KVGroupChecksum) DataAndIndexSumSize() (dataSize, indexSize uint64) {
 	for id, cksum := range c.m {
-		if id == DataKVGroupAsIndexID {
+		if id == DataKVGroupID {
 			dataSize = cksum.SumSize()
 		} else {
 			indexSize += cksum.SumSize()
@@ -218,7 +215,7 @@ func (c *KVGroupChecksum) DataAndIndexSumSize() (dataSize, indexSize uint64) {
 // DataAndIndexSumKVS returns the total number of data KV pairs and index KV pairs.
 func (c *KVGroupChecksum) DataAndIndexSumKVS() (dataKVS, indexKVS uint64) {
 	for id, cksum := range c.m {
-		if id == DataKVGroupAsIndexID {
+		if id == DataKVGroupID {
 			dataKVS = cksum.SumKVS()
 		} else {
 			indexKVS += cksum.SumKVS()
@@ -242,9 +239,9 @@ func (c *KVGroupChecksum) GetInnerChecksums() map[int64]*KVChecksum {
 	return m
 }
 
-// MergeGroup merges all groups of this checksum into a single KVChecksum.
-func (c *KVGroupChecksum) MergeGroup() KVChecksum {
-	merged := NewKVChecksum(0)
+// MergedChecksum merges all groups of this checksum into a single KVChecksum.
+func (c *KVGroupChecksum) MergedChecksum() KVChecksum {
+	merged := NewKVChecksum()
 	for _, cksum := range c.m {
 		merged.Add(cksum)
 	}
diff --git a/br/pkg/lightning/verification/checksum_test.go b/br/pkg/lightning/verification/checksum_test.go
index 57caca5d1284a..68adbf025cef6 100644
--- a/br/pkg/lightning/verification/checksum_test.go
+++ b/br/pkg/lightning/verification/checksum_test.go
@@ -25,7 +25,7 @@ import (
 )
 
 func TestChecksum(t *testing.T) {
-	checksum := verification.NewKVChecksum(0)
+	checksum := verification.NewKVChecksum()
 	require.Equal(t, uint64(0), checksum.Sum())
 
 	// checksum on nothing
@@ -99,7 +99,7 @@ func TestGroupChecksum(t *testing.T) {
 	inner := c.GetInnerChecksums()
 	require.Equal(t, 2, len(inner))
 	require.Equal(t, uint64(1), inner[1].SumKVS())
-	require.Equal(t, uint64(1), inner[verification.DataKVGroupAsIndexID].SumKVS())
+	require.Equal(t, uint64(1), inner[verification.DataKVGroupID].SumKVS())
 
 	keyspaceCodec := &mockCodec{keyspace: []byte("keyspace")}
 	keyspaceC := verification.NewKVGroupChecksumWithKeyspace(keyspaceCodec)
@@ -116,7 +116,7 @@ func TestGroupChecksum(t *testing.T) {
 	require.Equal(t, 3, len(inner))
 	require.Equal(t, uint64(2), inner[1].SumKVS())
 	require.Equal(t, uint64(1), inner[2].SumKVS())
-	require.Equal(t, uint64(1), inner[verification.DataKVGroupAsIndexID].SumKVS())
+	require.Equal(t, uint64(1), inner[verification.DataKVGroupID].SumKVS())
 
 	dataKVCnt, indexKVCnt := c.DataAndIndexSumKVS()
 	require.Equal(t, uint64(1), dataKVCnt)
@@ -126,7 +126,7 @@ func TestGroupChecksum(t *testing.T) {
 	require.Equal(t, uint64(6), dataSize)
 	require.Equal(t, uint64(22), indexSize)
 
-	merged := c.MergeGroup()
+	merged := c.MergedChecksum()
 	require.Equal(t, uint64(4), merged.SumKVS())
 	require.Equal(t, uint64(28), merged.SumSize())
 }
diff --git a/pkg/disttask/importinto/proto.go b/pkg/disttask/importinto/proto.go
index e83e91e84947c..88a53fbc19986 100644
--- a/pkg/disttask/importinto/proto.go
+++ b/pkg/disttask/importinto/proto.go
@@ -53,7 +53,7 @@ type ImportStepMeta struct {
 	// this is the engine ID, not the id in tidb_background_subtask table.
 	ID       int32
 	Chunks   []Chunk
-	Checksum map[int64]Checksum
+	Checksum map[int64]Checksum // see KVGroupChecksum for definition of map key.
 	Result   Result
 	// MaxIDs stores the max id that have been used during encoding for each allocator type.
 	// the max id is same among all allocator types for now, since we're using same base, see
@@ -94,7 +94,8 @@ type WriteIngestStepMeta struct {
 
 // PostProcessStepMeta is the meta of post process step.
 type PostProcessStepMeta struct {
-	// accumulated checksum of all subtasks in import step.
+	// accumulated checksum of all subtasks in import step. See KVGroupChecksum for
+	// definition of map key.
 	Checksum map[int64]Checksum
 	// MaxIDs of max all max-ids of subtasks in import step.
 	MaxIDs map[autoid.AllocatorType]int64
diff --git a/pkg/disttask/importinto/subtask_executor.go b/pkg/disttask/importinto/subtask_executor.go
index a10bf75fb7351..5202dc70d02d9 100644
--- a/pkg/disttask/importinto/subtask_executor.go
+++ b/pkg/disttask/importinto/subtask_executor.go
@@ -131,8 +131,8 @@ func postProcess(ctx context.Context, taskMeta *TaskMeta, subtaskMeta *PostProce
 	localChecksum := verify.NewKVGroupChecksumForAdd()
 	for id, cksum := range subtaskMeta.Checksum {
 		callLog.Info(
-			"group checksum",
-			zap.Int64("id", id),
+			"kv group checksum",
+			zap.Int64("groupId", id),
 			zap.Uint64("size", cksum.Size),
 			zap.Uint64("kvs", cksum.KVs),
 			zap.Uint64("checksum", cksum.Sum),
@@ -146,6 +146,6 @@ func postProcess(ctx context.Context, taskMeta *TaskMeta, subtaskMeta *PostProce
 		return err
 	}
 	return taskManager.WithNewSession(func(se sessionctx.Context) error {
-		return importer.VerifyChecksum(ctx, &taskMeta.Plan, localChecksum.MergeGroup(), se, logger)
+		return importer.VerifyChecksum(ctx, &taskMeta.Plan, localChecksum.MergedChecksum(), se, logger)
 	})
 }
diff --git a/pkg/disttask/importinto/task_executor.go b/pkg/disttask/importinto/task_executor.go
index 14089f942095d..c13b7ddd56458 100644
--- a/pkg/disttask/importinto/task_executor.go
+++ b/pkg/disttask/importinto/task_executor.go
@@ -232,9 +232,6 @@ func (s *importStepExecutor) OnFinished(ctx context.Context, subtask *proto.Subt
 			KVs:  c.SumKVS(),
 			Size: c.SumSize(),
 		}
-		if s.tableImporter.IsGlobalSort() && id == verification.DataKVGroupAsIndexID {
-			dataKVCount = c.SumKVS()
-		}
 	}
 	subtaskMeta.Result = Result{
 		LoadedRowCnt: dataKVCount,
diff --git a/pkg/executor/importer/chunk_process.go b/pkg/executor/importer/chunk_process.go
index 45c499ab01143..b456472a27d0b 100644
--- a/pkg/executor/importer/chunk_process.go
+++ b/pkg/executor/importer/chunk_process.go
@@ -169,6 +169,7 @@ func (b *encodedKVGroupBatch) add(kvs *kv.Pairs) error {
 // chunkEncoder encodes data from readFn and sends encoded data to sendFn.
 type chunkEncoder struct {
 	readFn encodeReaderFn
+	offset int64
 	sendFn func(ctx context.Context, batch *encodedKVGroupBatch) error
 
 	chunkName string
@@ -186,6 +187,7 @@ type chunkEncoder struct {
 func newChunkEncoder(
 	chunkName string,
 	readFn encodeReaderFn,
+	offset int64,
 	sendFn func(ctx context.Context, batch *encodedKVGroupBatch) error,
 	logger *zap.Logger,
 	encoder KVEncoder,
@@ -194,6 +196,7 @@ func newChunkEncoder(
 	return &chunkEncoder{
 		chunkName:     chunkName,
 		readFn:        readFn,
+		offset:        offset,
 		sendFn:        sendFn,
 		logger:        logger,
 		encoder:       encoder,
@@ -209,7 +212,7 @@ func (p *chunkEncoder) encodeLoop(ctx context.Context) error {
 		rowCount                                int
 		rowBatch                                = make([]*kv.Pairs, 0, MinDeliverRowCnt)
 		rowBatchByteSize                        uint64
-		currOffset, prevOffset                  int64
+		currOffset                              int64
 	)
 	metrics, _ := metric.GetCommonMetric(ctx)
 	if metrics != nil {
@@ -224,8 +227,8 @@ func (p *chunkEncoder) encodeLoop(ctx context.Context) error {
 		}
 
 		if currOffset >= 0 && metrics != nil {
-			delta := currOffset - prevOffset
-			prevOffset = currOffset
+			delta := currOffset - p.offset
+			p.offset = currOffset
 			// if we're using split_file, this metric might larger than total
 			// source file size, as the offset we're using is the reader offset,
 			// not parser offset, and we'll buffer data.
@@ -378,6 +381,7 @@ func NewFileChunkProcessor(
 		enc: newChunkEncoder(
 			chunk.GetKey(),
 			parserEncodeReader(parser, chunk.Chunk.EndOffset, chunk.GetKey()),
+			chunk.Chunk.Offset,
 			deliver.sendEncodedData,
 			chunkLogger,
 			encoder,
@@ -522,6 +526,7 @@ func newQueryChunkProcessor(
 		enc: newChunkEncoder(
 			chunkName,
 			queryRowEncodeReader(rowCh),
+			-1,
 			deliver.sendEncodedData,
 			chunkLogger,
 			encoder,
diff --git a/pkg/executor/importer/importer_testkit_test.go b/pkg/executor/importer/importer_testkit_test.go
index f8da189ac6e70..7665238bc2916 100644
--- a/pkg/executor/importer/importer_testkit_test.go
+++ b/pkg/executor/importer/importer_testkit_test.go
@@ -225,11 +225,11 @@ func TestPostProcess(t *testing.T) {
 
 	// verify checksum failed
 	localChecksum := verify.NewKVGroupChecksumForAdd()
-	localChecksum.AddRawGroup(verify.DataKVGroupAsIndexID, 1, 2, 1)
+	localChecksum.AddRawGroup(verify.DataKVGroupID, 1, 2, 1)
 	require.ErrorIs(t, importer.PostProcess(ctx, tk.Session(), nil, plan, localChecksum, logger), common.ErrChecksumMismatch)
 	// success
 	localChecksum = verify.NewKVGroupChecksumForAdd()
-	localChecksum.AddRawGroup(verify.DataKVGroupAsIndexID, 1, 1, 1)
+	localChecksum.AddRawGroup(verify.DataKVGroupID, 1, 1, 1)
 	require.NoError(t, importer.PostProcess(ctx, tk.Session(), nil, plan, localChecksum, logger))
 	// get KV store failed
 	importer.GetKVStore = func(path string, tls kvconfig.Security) (kv.Storage, error) {
@@ -328,7 +328,7 @@ func TestProcessChunkWith(t *testing.T) {
 		require.Len(t, progress.GetColSize(), 3)
 		checksumMap := checksum.GetInnerChecksums()
 		require.Len(t, checksumMap, 1)
-		require.Equal(t, verify.MakeKVChecksum(74, 2, 15625182175392723123), *checksumMap[verify.DataKVGroupAsIndexID])
+		require.Equal(t, verify.MakeKVChecksum(74, 2, 15625182175392723123), *checksumMap[verify.DataKVGroupID])
 	})
 
 	t.Run("query chunk", func(t *testing.T) {
@@ -360,7 +360,7 @@ func TestProcessChunkWith(t *testing.T) {
 		require.Len(t, progress.GetColSize(), 3)
 		checksumMap := checksum.GetInnerChecksums()
 		require.Len(t, checksumMap, 1)
-		require.Equal(t, verify.MakeKVChecksum(111, 3, 14231358899564314836), *checksumMap[verify.DataKVGroupAsIndexID])
+		require.Equal(t, verify.MakeKVChecksum(111, 3, 14231358899564314836), *checksumMap[verify.DataKVGroupID])
 	})
 }
 
diff --git a/pkg/executor/importer/table_import.go b/pkg/executor/importer/table_import.go
index 31491d6afeba9..15214346a3b01 100644
--- a/pkg/executor/importer/table_import.go
+++ b/pkg/executor/importer/table_import.go
@@ -801,7 +801,7 @@ func PostProcess(
 		return err
 	}
 
-	return VerifyChecksum(ctx, plan, localChecksum.MergeGroup(), se, logger)
+	return VerifyChecksum(ctx, plan, localChecksum.MergedChecksum(), se, logger)
 }
 
 type autoIDRequirement struct {