diff --git a/drainer/metrics.go b/drainer/metrics.go
index 978c8e3d5..685ade1fb 100644
--- a/drainer/metrics.go
+++ b/drainer/metrics.go
@@ -14,6 +14,7 @@
 package drainer
 
 import (
+	"github.com/pingcap/tidb-binlog/drainer/sync"
 	bf "github.com/pingcap/tidb-binlog/pkg/binlogfile"
 	"github.com/prometheus/client_golang/prometheus"
 )
@@ -124,6 +125,8 @@ var (
 var registry = prometheus.NewRegistry()
 
 func init() {
+	sync.QueueSizeGauge = queueSizeGauge
+
 	registry.MustRegister(prometheus.NewProcessCollector(prometheus.ProcessCollectorOpts{}))
 	registry.MustRegister(prometheus.NewGoCollector())
 	registry.MustRegister(pumpPositionGauge)
diff --git a/drainer/sync/mysql.go b/drainer/sync/mysql.go
index a85c59269..fb1d12799 100644
--- a/drainer/sync/mysql.go
+++ b/drainer/sync/mysql.go
@@ -30,6 +30,9 @@ import (
 
 var _ Syncer = &MysqlSyncer{}
 
+// QueueSizeGauge to be used.
+var QueueSizeGauge *prometheus.GaugeVec
+
 // MysqlSyncer sync binlog to Mysql
 type MysqlSyncer struct {
 	db      *sql.DB
@@ -60,9 +63,12 @@ func CreateLoader(
 		opts = append(opts, loader.Metrics(&loader.MetricsGroup{
 			QueryHistogramVec: queryHistogramVec,
 			EventCounterVec:   nil,
+			QueueSizeGauge:    QueueSizeGauge,
 		}))
 	}
 
+	opts = append(opts, loader.Merge(cfg.Merge))
+
 	if cfg.SyncMode != 0 {
 		mode := loader.SyncMode(cfg.SyncMode)
 		opts = append(opts, loader.SyncModeOption(mode))
diff --git a/drainer/sync/util.go b/drainer/sync/util.go
index 7c2892ee1..0f46d30cb 100644
--- a/drainer/sync/util.go
+++ b/drainer/sync/util.go
@@ -35,6 +35,8 @@ type DBConfig struct {
 	Checkpoint        CheckpointConfig `toml:"checkpoint" json:"checkpoint"`
 	BinlogFileDir     string           `toml:"dir" json:"dir"`
 
+	Merge bool `toml:"merge" json:"merge"`
+
 	ZKAddrs          string `toml:"zookeeper-addrs" json:"zookeeper-addrs"`
 	KafkaAddrs       string `toml:"kafka-addrs" json:"kafka-addrs"`
 	KafkaVersion     string `toml:"kafka-version" json:"kafka-version"`
diff --git a/go.mod b/go.mod
index 7ea00f048..3a90acd17 100644
--- a/go.mod
+++ b/go.mod
@@ -32,7 +32,6 @@ require (
 	github.com/sirupsen/logrus v1.4.1 // indirect
 	github.com/soheilhy/cmux v0.1.4
 	github.com/syndtr/goleveldb v1.0.1-0.20190625010220-02440ea7a285
-	github.com/tmc/grpc-websocket-proxy v0.0.0-20190109142713-0ad062ec5ee5 // indirect
 	github.com/unrolled/render v0.0.0-20180914162206-b9786414de4d
 	go.etcd.io/etcd v0.5.0-alpha.5.0.20190320044326-77d4b742cdbf
 	go.uber.org/atomic v1.5.1 // indirect
diff --git a/go.sum b/go.sum
index 2a9044fe1..f5529bfb9 100644
--- a/go.sum
+++ b/go.sum
@@ -281,9 +281,8 @@ github.com/syndtr/goleveldb v1.0.1-0.20190625010220-02440ea7a285 h1:uSDYjYejelKy
 github.com/syndtr/goleveldb v1.0.1-0.20190625010220-02440ea7a285/go.mod h1:9OrXJhf154huy1nPWmuSrkgjPUtUNhA+Zmy+6AESzuA=
 github.com/tiancaiamao/appdash v0.0.0-20181126055449-889f96f722a2/go.mod h1:2PfKggNGDuadAa0LElHrByyrz4JPZ9fFx6Gs7nx7ZZU=
 github.com/tmc/grpc-websocket-proxy v0.0.0-20170815181823-89b8d40f7ca8/go.mod h1:ncp9v5uamzpCO7NfCPTXjqaC+bZgJeR0sMTm6dMHP7U=
+github.com/tmc/grpc-websocket-proxy v0.0.0-20171017195756-830351dc03c6 h1:lYIiVDtZnyTWlNwiAxLj0bbpTcx1BWCFhXjfsvmPdNc=
 github.com/tmc/grpc-websocket-proxy v0.0.0-20171017195756-830351dc03c6/go.mod h1:ncp9v5uamzpCO7NfCPTXjqaC+bZgJeR0sMTm6dMHP7U=
-github.com/tmc/grpc-websocket-proxy v0.0.0-20190109142713-0ad062ec5ee5 h1:LnC5Kc/wtumK+WB441p7ynQJzVuNRJiqddSIE3IlSEQ=
-github.com/tmc/grpc-websocket-proxy v0.0.0-20190109142713-0ad062ec5ee5/go.mod h1:ncp9v5uamzpCO7NfCPTXjqaC+bZgJeR0sMTm6dMHP7U=
 github.com/uber-go/atomic v1.3.2 h1:Azu9lPBWRNKzYXSIwRfgRuDuS0YKsK4NFhiQv98gkxo=
 github.com/uber-go/atomic v1.3.2/go.mod h1:/Ct5t2lcmbJ4OSe/waGBoaVvVqtO0bmtfVNex1PFV8g=
 github.com/uber/jaeger-client-go v2.15.0+incompatible h1:NP3qsSqNxh8VYr956ur1N/1C1PjvOJnJykCzcD5QHbk=
diff --git a/pkg/loader/load.go b/pkg/loader/load.go
index a1e1569fa..2dbcb6af5 100644
--- a/pkg/loader/load.go
+++ b/pkg/loader/load.go
@@ -17,6 +17,7 @@ import (
 	"context"
 	gosql "database/sql"
 	"fmt"
+	"strconv"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -102,6 +103,7 @@ type loaderImpl struct {
 type MetricsGroup struct {
 	EventCounterVec   *prometheus.CounterVec
 	QueryHistogramVec *prometheus.HistogramVec
+	QueueSizeGauge    *prometheus.GaugeVec
 }
 
 // SyncMode represents the sync mode of DML.
@@ -120,6 +122,7 @@ type options struct {
 	metrics          *MetricsGroup
 	saveAppliedTS    bool
 	syncMode         SyncMode
+	merge            bool
 }
 
 var defaultLoaderOptions = options{
@@ -129,6 +132,7 @@ var defaultLoaderOptions = options{
 	metrics:          nil,
 	saveAppliedTS:    false,
 	syncMode:         SyncFullColumn,
+	merge:            false,
 }
 
 // A Option sets options such batch size, worker count etc.
@@ -155,6 +159,13 @@ func BatchSize(n int) Option {
 	}
 }
 
+// Merge set merge options.
+func Merge(v bool) Option {
+	return func(o *options) {
+		o.merge = v
+	}
+}
+
 //SetloopBackSyncInfo set loop back sync info of loader
 func SetloopBackSyncInfo(loopBackSyncInfo *loopbacksync.LoopBackSync) Option {
 	return func(o *options) {
@@ -196,11 +207,10 @@ func NewLoader(db *gosql.DB, opt ...Option) (Loader, error) {
 		loopBackSyncInfo: opts.loopBackSyncInfo,
 		input:            make(chan *Txn),
 		successTxn:       make(chan *Txn),
-		merge:            true,
+		merge:            opts.merge,
 		saveAppliedTS:    opts.saveAppliedTS,
-
-		ctx:    ctx,
-		cancel: cancel,
+		ctx:              ctx,
+		cancel:           cancel,
 	}
 
 	db.SetMaxOpenConns(opts.workerCount)
@@ -430,6 +440,14 @@ func (s *loaderImpl) singleExec(executor *executor, dmls []*DML) error {
 
 	}
 
+	if s.metrics != nil && s.metrics.QueueSizeGauge != nil {
+		// limit 10 sample
+		for i := 0; i < len(byHash) && i < 10; i++ {
+			name := "worker_" + strconv.Itoa(i)
+			s.metrics.QueueSizeGauge.WithLabelValues(name).Set(float64(len(byHash[i])))
+		}
+	}
+
 	err := s.execByHash(executor, byHash)
 	return errors.Trace(err)
 }
@@ -513,7 +531,7 @@ func (s *loaderImpl) Run() error {
 		}()
 	}
 
-	txnManager := newTxnManager(1024, s.input)
+	txnManager := newTxnManager(100*1024 /* limit dml number */, s.input)
 	defer txnManager.Close()
 
 	batch := fNewBatchManager(s)
@@ -572,7 +590,7 @@ func (s *loaderImpl) groupDMLs(dmls []*DML) (batchByTbls map[string][]*DML, sing
 	batchByTbls = make(map[string][]*DML)
 	for _, dml := range dmls {
 		info := dml.info
-		if info.primaryKey != nil && len(info.uniqueKeys) == 0 {
+		if info.primaryKey != nil {
 			tblName := dml.TableName()
 			batchByTbls[tblName] = append(batchByTbls[tblName], dml)
 		} else {