diff --git a/loader/checkpoint.go b/loader/checkpoint.go
index d34698c8d2..1b54821036 100644
--- a/loader/checkpoint.go
+++ b/loader/checkpoint.go
@@ -17,6 +17,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/pingcap/dm/dm/config"
@@ -69,6 +70,10 @@ type CheckPoint interface {
 // RemoteCheckPoint implements CheckPoint by saving status in remote database system, mostly in TiDB.
 // it's not thread-safe
 type RemoteCheckPoint struct {
+	// used to protect database operation with `conn`.
+	// if more operations need to be protected, add another mutex or rename this one.
+	connMutex sync.Mutex
+
 	db             *conn.BaseDB
 	conn           *DBConn
 	id             string
@@ -118,7 +123,9 @@ func (cp *RemoteCheckPoint) prepare(tctx *tcontext.Context) error {
 
 func (cp *RemoteCheckPoint) createSchema(tctx *tcontext.Context) error {
 	sql2 := fmt.Sprintf("CREATE SCHEMA IF NOT EXISTS `%s`", cp.schema)
+	cp.connMutex.Lock()
 	err := cp.conn.executeSQL(tctx, []string{sql2})
+	cp.connMutex.Unlock()
 	return terror.WithScope(err, terror.ScopeDownstream)
 }
 
@@ -137,7 +144,9 @@ func (cp *RemoteCheckPoint) createTable(tctx *tcontext.Context) error {
 	);
 `
 	sql2 := fmt.Sprintf(createTable, tableName)
+	cp.connMutex.Lock()
 	err := cp.conn.executeSQL(tctx, []string{sql2})
+	cp.connMutex.Unlock()
 	return terror.WithScope(err, terror.ScopeDownstream)
 }
 
@@ -149,7 +158,9 @@ func (cp *RemoteCheckPoint) Load(tctx *tcontext.Context) error {
 	}()
 
 	query := fmt.Sprintf("SELECT `filename`,`cp_schema`,`cp_table`,`offset`,`end_pos` from `%s`.`%s` where `id`=?", cp.schema, cp.table)
+	cp.connMutex.Lock()
 	rows, err := cp.conn.querySQL(tctx, query, cp.id)
+	cp.connMutex.Unlock()
 	if err != nil {
 		return terror.WithScope(err, terror.ScopeDownstream)
 	}
@@ -277,7 +288,7 @@ func (cp *RemoteCheckPoint) Init(tctx *tcontext.Context, filename string, endPos
 
 	// fields[0] -> db name, fields[1] -> table name
 	sql2 := fmt.Sprintf("INSERT INTO `%s`.`%s` (`id`, `filename`, `cp_schema`, `cp_table`, `offset`, `end_pos`) VALUES(?,?,?,?,?,?)", cp.schema, cp.table)
-	cp.logCtx.L().Debug("initial checkpoint record",
+	cp.logCtx.L().Info("initial checkpoint record",
 		zap.String("sql", sql2),
 		zap.String("id", cp.id),
 		zap.String("filename", filename),
@@ -286,7 +297,9 @@ func (cp *RemoteCheckPoint) Init(tctx *tcontext.Context, filename string, endPos
 		zap.Int64("offset", 0),
 		zap.Int64("end position", endPos))
 	args := []interface{}{cp.id, filename, fields[0], fields[1], 0, endPos}
+	cp.connMutex.Lock()
 	err := cp.conn.executeSQL(tctx, []string{sql2}, args)
+	cp.connMutex.Unlock()
 	if err != nil {
 		if isErrDupEntry(err) {
 			cp.logCtx.L().Info("checkpoint record already exists, skip it.", zap.String("id", cp.id), zap.String("filename", filename))
@@ -299,6 +312,8 @@ func (cp *RemoteCheckPoint) Init(tctx *tcontext.Context, filename string, endPos
 
 // ResetConn implements CheckPoint.ResetConn
 func (cp *RemoteCheckPoint) ResetConn(tctx *tcontext.Context) error {
+	cp.connMutex.Lock()
+	defer cp.connMutex.Unlock()
 	return cp.conn.resetConn(tctx)
 }
 
@@ -320,14 +335,18 @@ func (cp *RemoteCheckPoint) GenSQL(filename string, offset int64) string {
 // Clear implements CheckPoint.Clear
 func (cp *RemoteCheckPoint) Clear(tctx *tcontext.Context) error {
 	sql2 := fmt.Sprintf("DELETE FROM `%s`.`%s` WHERE `id` = '%s'", cp.schema, cp.table, cp.id)
+	cp.connMutex.Lock()
 	err := cp.conn.executeSQL(tctx, []string{sql2})
+	cp.connMutex.Unlock()
 	return terror.WithScope(err, terror.ScopeDownstream)
 }
 
 // Count implements CheckPoint.Count
 func (cp *RemoteCheckPoint) Count(tctx *tcontext.Context) (int, error) {
 	query := fmt.Sprintf("SELECT COUNT(id) FROM `%s`.`%s` WHERE `id` = ?", cp.schema, cp.table)
+	cp.connMutex.Lock()
 	rows, err := cp.conn.querySQL(tctx, query, cp.id)
+	cp.connMutex.Unlock()
 	if err != nil {
 		return 0, terror.WithScope(err, terror.ScopeDownstream)
 	}
diff --git a/loader/loader.go b/loader/loader.go
index af668749ad..905b7d1f29 100644
--- a/loader/loader.go
+++ b/loader/loader.go
@@ -256,7 +256,7 @@ func (w *Worker) dispatchSQL(ctx context.Context, file string, offset int64, tab
 	baseFile := filepath.Base(file)
 	err = w.checkPoint.Init(w.tctx.WithContext(ctx), baseFile, finfo.Size())
 	if err != nil {
-		w.tctx.L().Error("fail to initial checkpoint", zap.String("data file", file), log.ShortError(err))
+		w.tctx.L().Error("fail to initial checkpoint", zap.String("data file", file), zap.Int64("offset", offset), log.ShortError(err))
 		return err
 	}
 
@@ -273,7 +273,7 @@ func (w *Worker) dispatchSQL(ctx context.Context, file string, offset int64, tab
 	for {
 		select {
 		case <-ctx.Done():
-			w.tctx.L().Info("sql dispatcher is ready to quit.", zap.String("data file", file))
+			w.tctx.L().Info("sql dispatcher is ready to quit.", zap.String("data file", file), zap.Int64("offset", offset))
 			return nil
 		default:
 			// do nothing
@@ -282,7 +282,7 @@ func (w *Worker) dispatchSQL(ctx context.Context, file string, offset int64, tab
 		cur += int64(len(line))
 
 		if err == io.EOF {
-			w.tctx.L().Info("data are scanned finished.", zap.String("data file", file))
+			w.tctx.L().Info("data are scanned finished.", zap.String("data file", file), zap.Int64("offset", offset))
 			break
 		}