diff --git a/store/mockstore/mocktikv/errors.go b/store/mockstore/mocktikv/errors.go
index 5f10ac74d7e6f..8f15c0f689b16 100644
--- a/store/mockstore/mocktikv/errors.go
+++ b/store/mockstore/mocktikv/errors.go
@@ -22,6 +22,7 @@ type ErrLocked struct {
 	Primary []byte
 	StartTS uint64
 	TTL     uint64
+	TxnSize uint64
 }
 
 // Error formats the lock to a string.
diff --git a/store/mockstore/mocktikv/mvcc.go b/store/mockstore/mocktikv/mvcc.go
index fda5c5597915a..576bfc4b744c6 100644
--- a/store/mockstore/mocktikv/mvcc.go
+++ b/store/mockstore/mocktikv/mvcc.go
@@ -69,6 +69,7 @@ func (l *mvccLock) MarshalBinary() ([]byte, error) {
 	mh.WriteNumber(&buf, l.op)
 	mh.WriteNumber(&buf, l.ttl)
 	mh.WriteNumber(&buf, l.forUpdateTS)
+	mh.WriteNumber(&buf, l.txnSize)
 	return buf.Bytes(), errors.Trace(mh.err)
 }
 
@@ -82,6 +83,7 @@ func (l *mvccLock) UnmarshalBinary(data []byte) error {
 	mh.ReadNumber(buf, &l.op)
 	mh.ReadNumber(buf, &l.ttl)
 	mh.ReadNumber(buf, &l.forUpdateTS)
+	mh.ReadNumber(buf, &l.txnSize)
 	return errors.Trace(mh.err)
 }
 
@@ -198,6 +200,7 @@ func (l *mvccLock) lockErr(key []byte) error {
 		Primary: l.primary,
 		StartTS: l.startTS,
 		TTL:     l.ttl,
+		TxnSize: l.txnSize,
 	}
 }
 
diff --git a/store/mockstore/mocktikv/mvcc_leveldb.go b/store/mockstore/mocktikv/mvcc_leveldb.go
index 1d8edc49d4536..be550fcb8b4a0 100644
--- a/store/mockstore/mocktikv/mvcc_leveldb.go
+++ b/store/mockstore/mocktikv/mvcc_leveldb.go
@@ -634,7 +634,7 @@ func (mvcc *MVCCLevelDB) Prewrite(req *kvrpcpb.PrewriteRequest) []error {
 	anyError := false
 	batch := &leveldb.Batch{}
 	errs := make([]error, 0, len(mutations))
-	txnSize := len(mutations)
+	txnSize := req.TxnSize
 	for i, m := range mutations {
 		// If the operation is Insert, check if key is exists at first.
 		var err error
@@ -655,7 +655,7 @@ func (mvcc *MVCCLevelDB) Prewrite(req *kvrpcpb.PrewriteRequest) []error {
 			}
 		}
 		isPessimisticLock := len(req.IsPessimisticLock) > 0 && req.IsPessimisticLock[i]
-		err = prewriteMutation(mvcc.db, batch, m, startTS, primary, ttl, uint64(txnSize), isPessimisticLock)
+		err = prewriteMutation(mvcc.db, batch, m, startTS, primary, ttl, txnSize, isPessimisticLock)
 		errs = append(errs, err)
 		if err != nil {
 			anyError = true
diff --git a/store/mockstore/mocktikv/rpc.go b/store/mockstore/mocktikv/rpc.go
index e4919318048fa..f8396a5887e94 100644
--- a/store/mockstore/mocktikv/rpc.go
+++ b/store/mockstore/mocktikv/rpc.go
@@ -57,6 +57,7 @@ func convertToKeyError(err error) *kvrpcpb.KeyError {
 				PrimaryLock: locked.Primary,
 				LockVersion: locked.StartTS,
 				LockTtl:     locked.TTL,
+				TxnSize:     locked.TxnSize,
 			},
 		}
 	}
diff --git a/store/tikv/2pc.go b/store/tikv/2pc.go
index b4047fea0c1d3..a5434f9691946 100644
--- a/store/tikv/2pc.go
+++ b/store/tikv/2pc.go
@@ -88,26 +88,29 @@ type twoPhaseCommitter struct {
 	mutations map[string]*mutationEx
 	lockTTL   uint64
 	commitTS  uint64
-	mu        struct {
-		sync.RWMutex
-		committed       bool
-		undeterminedErr error // undeterminedErr saves the rpc error we encounter when commit primary key.
-	}
-	priority pb.CommandPri
-	syncLog  bool
-	connID   uint64 // connID is used for log.
-	cleanWg  sync.WaitGroup
+	priority  pb.CommandPri
+	connID    uint64 // connID is used for log.
+	cleanWg   sync.WaitGroup
 	// maxTxnTimeUse represents max time a Txn may use (in ms) from its startTS to commitTS.
 	// We use it to guarantee GC worker will not influence any active txn. The value
 	// should be less than GC life time.
-	maxTxnTimeUse uint64
-	detail        *execdetails.CommitDetails
-	// For pessimistic transaction
-	isPessimistic  bool
+	maxTxnTimeUse  uint64
+	detail         *execdetails.CommitDetails
 	primaryKey     []byte
 	forUpdateTS    uint64
-	isFirstLock    bool
 	pessimisticTTL uint64
+
+	mu struct {
+		sync.RWMutex
+		undeterminedErr error // undeterminedErr saves the rpc error we encounter when commit primary key.
+		committed       bool
+	}
+	syncLog bool
+	// For pessimistic transaction
+	isPessimistic bool
+	isFirstLock   bool
+	// regionTxnSize stores the number of keys involved in each region
+	regionTxnSize map[uint64]int
 }
 
 type mutationEx struct {
@@ -119,10 +122,11 @@ type mutationEx struct {
 // newTwoPhaseCommitter creates a twoPhaseCommitter.
 func newTwoPhaseCommitter(txn *tikvTxn, connID uint64) (*twoPhaseCommitter, error) {
 	return &twoPhaseCommitter{
-		store:   txn.store,
-		txn:     txn,
-		startTS: txn.StartTS(),
-		connID:  connID,
+		store:         txn.store,
+		txn:           txn,
+		startTS:       txn.StartTS(),
+		connID:        connID,
+		regionTxnSize: map[uint64]int{},
 	}, nil
 }
 
@@ -323,6 +327,9 @@ func (c *twoPhaseCommitter) doActionOnKeys(bo *Backoffer, action twoPhaseCommitA
 	var batches []batchKeys
 	var sizeFunc = c.keySize
 	if action == actionPrewrite {
+		for region, keys := range groups {
+			c.regionTxnSize[region.id] = len(keys)
+		}
 		sizeFunc = c.keyValueSize
 		atomic.AddInt32(&c.detail.PrewriteRegionNum, int32(len(groups)))
 	}
@@ -461,7 +468,7 @@ func (c *twoPhaseCommitter) keySize(key []byte) int {
 	return len(key)
 }
 
-func (c *twoPhaseCommitter) buildPrewriteRequest(batch batchKeys) *tikvrpc.Request {
+func (c *twoPhaseCommitter) buildPrewriteRequest(batch batchKeys, txnSize uint64) *tikvrpc.Request {
 	mutations := make([]*pb.Mutation, len(batch.keys))
 	var isPessimisticLock []bool
 	if c.isPessimistic {
@@ -483,7 +490,7 @@ func (c *twoPhaseCommitter) buildPrewriteRequest(batch batchKeys) *tikvrpc.Reque
 			LockTtl:           c.lockTTL,
 			IsPessimisticLock: isPessimisticLock,
 			ForUpdateTs:       c.forUpdateTS,
-			TxnSize:           uint64(len(batch.keys)),
+			TxnSize:           txnSize,
 		},
 		Context: pb.Context{
 			Priority: c.priority,
@@ -493,7 +500,14 @@ func (c *twoPhaseCommitter) buildPrewriteRequest(batch batchKeys) *tikvrpc.Reque
 }
 
 func (c *twoPhaseCommitter) prewriteSingleBatch(bo *Backoffer, batch batchKeys) error {
-	req := c.buildPrewriteRequest(batch)
+	txnSize := uint64(c.regionTxnSize[batch.region.id])
+	// When we retry because of a region miss, we don't know the transaction size. We set the transaction size here
+	// to MaxUint64 to avoid unexpected "resolve lock lite".
+	if len(bo.errors) > 0 {
+		txnSize = math.MaxUint64
+	}
+
+	req := c.buildPrewriteRequest(batch, txnSize)
 	for {
 		resp, err := c.store.SendReq(bo, req, batch.region, readTimeoutShort)
 		if err != nil {
diff --git a/store/tikv/2pc_test.go b/store/tikv/2pc_test.go
index 9fb990cc749e6..a92f33fdff9fd 100644
--- a/store/tikv/2pc_test.go
+++ b/store/tikv/2pc_test.go
@@ -442,6 +442,40 @@ func (s *testCommitterSuite) TestWrittenKeysOnConflict(c *C) {
 	c.Assert(totalTime, Less, time.Millisecond*200)
 }
 
+func (s *testCommitterSuite) TestPrewriteTxnSize(c *C) {
+	// Prepare two regions first: (, 100) and [100, )
+	region, _ := s.cluster.GetRegionByKey([]byte{50})
+	newRegionID := s.cluster.AllocID()
+	newPeerID := s.cluster.AllocID()
+	s.cluster.Split(region.Id, newRegionID, []byte{100}, []uint64{newPeerID}, newPeerID)
+
+	txn := s.begin(c)
+	var val [1024]byte
+	for i := byte(50); i < 120; i++ {
+		err := txn.Set([]byte{i}, val[:])
+		c.Assert(err, IsNil)
+	}
+
+	commiter, err := newTwoPhaseCommitterWithInit(txn, 1)
+	c.Assert(err, IsNil)
+
+	ctx := context.Background()
+	err = commiter.prewriteKeys(NewBackoffer(ctx, prewriteMaxBackoff), commiter.keys)
+	c.Assert(err, IsNil)
+
+	// Check the written locks in the first region (50 keys)
+	for i := byte(50); i < 100; i++ {
+		lock := s.getLockInfo(c, []byte{i})
+		c.Assert(int(lock.TxnSize), Equals, 50)
+	}
+
+	// Check the written locks in the second region (20 keys)
+	for i := byte(100); i < 120; i++ {
+		lock := s.getLockInfo(c, []byte{i})
+		c.Assert(int(lock.TxnSize), Equals, 20)
+	}
+}
+
 func (s *testCommitterSuite) TestPessimisticPrewriteRequest(c *C) {
 	// This test checks that the isPessimisticLock field is set in the request even when no keys are pessimistic lock.
 	txn := s.begin(c)
@@ -454,7 +488,7 @@ func (s *testCommitterSuite) TestPessimisticPrewriteRequest(c *C) {
 	var batch batchKeys
 	batch.keys = append(batch.keys, []byte("t1"))
 	batch.region = RegionVerID{1, 1, 1}
-	req := commiter.buildPrewriteRequest(batch)
+	req := commiter.buildPrewriteRequest(batch, 1)
 	c.Assert(len(req.Prewrite.IsPessimisticLock), Greater, 0)
 	c.Assert(req.Prewrite.ForUpdateTs, Equals, uint64(100))
 }
@@ -520,7 +554,7 @@ func (s *testCommitterSuite) getLockInfo(c *C, key []byte) *kvrpcpb.LockInfo {
 	loc, err := s.store.regionCache.LocateKey(bo, key)
 	c.Assert(err, IsNil)
 	batch := batchKeys{region: loc.Region, keys: [][]byte{key}}
-	req := commiter.buildPrewriteRequest(batch)
+	req := commiter.buildPrewriteRequest(batch, 1)
 	resp, err := s.store.SendReq(bo, req, loc.Region, readTimeoutShort)
 	c.Assert(err, IsNil)
 	c.Assert(resp.Prewrite, NotNil)