diff --git a/server/client_resp.go b/server/client_resp.go
index 078a02c..93edef9 100644
--- a/server/client_resp.go
+++ b/server/client_resp.go
@@ -51,7 +51,10 @@ func (c *respClient) run() {
 			log.Fatal("client run panic %s:%v", buf, e)
 		}
 
+		handleQuit := true
 		if c.conn != nil {
+			//if handle quit command before, conn is nil
+			handleQuit = false
 			c.conn.Close()
 		}
 
@@ -60,7 +63,7 @@ func (c *respClient) run() {
 			c.tx = nil
 		}
 
-		c.app.removeSlave(c.client)
+		c.app.removeSlave(c.client, handleQuit)
 	}()
 
 	for {
@@ -144,6 +147,7 @@ func (c *respClient) handleRequest(reqData [][]byte) {
 		c.resp.writeStatus(OK)
 		c.resp.flush()
 		c.conn.Close()
+		c.conn = nil
 		return
 	}
 
diff --git a/server/cmd_replication.go b/server/cmd_replication.go
index 20c6982..aefd1ac 100644
--- a/server/cmd_replication.go
+++ b/server/cmd_replication.go
@@ -109,7 +109,16 @@ func syncCommand(c *client) error {
 
 	c.lastLogID = logId - 1
 
-	c.app.slaveAck(c)
+	stat, err := c.app.ldb.ReplicationStat()
+	if err != nil {
+		return err
+	}
+
+	if c.lastLogID > stat.LastID {
+		return fmt.Errorf("invalid sync logid %d > %d + 1", logId, stat.LastID)
+	} else if c.lastLogID == stat.LastID {
+		c.app.slaveAck(c)
+	}
 
 	c.syncBuf.Reset()
 
diff --git a/server/replication.go b/server/replication.go
index ea5f6cf..25e4a8d 100644
--- a/server/replication.go
+++ b/server/replication.go
@@ -50,10 +50,17 @@ func newMaster(app *App) *master {
 	return m
 }
 
+var (
+	quitCmd = []byte("*1\r\n$4\r\nquit\r\n")
+)
+
 func (m *master) Close() {
 	ledis.AsyncNotify(m.quit)
 
 	if m.conn != nil {
+		//for replication, we send quit command to close gracefully
+		m.conn.Write(quitCmd)
+
 		m.conn.Close()
 		m.conn = nil
 	}
@@ -321,7 +328,7 @@ func (app *App) addSlave(c *client) {
 	app.slaves[addr] = c
 }
 
-func (app *App) removeSlave(c *client) {
+func (app *App) removeSlave(c *client, activeQuit bool) {
 	addr := c.slaveListeningAddr
 
 	app.slock.Lock()
@@ -330,6 +337,9 @@ func (app *App) removeSlave(c *client) {
 	if _, ok := app.slaves[addr]; ok {
 		delete(app.slaves, addr)
 		log.Info("remove slave %s", addr)
+		if activeQuit {
+			asyncNotifyUint64(app.slaveSyncAck, c.lastLogID)
+		}
 	}
 }
 
@@ -344,7 +354,6 @@ func (app *App) slaveAck(c *client) {
 		return
 	}
 
-	println("ack", c.lastLogID)
 	asyncNotifyUint64(app.slaveSyncAck, c.lastLogID)
 }
 
@@ -371,9 +380,11 @@ func (app *App) publishNewLog(l *rpl.Log) {
 	n := 0
 	logId := l.ID
 	for _, s := range app.slaves {
-		if s.lastLogID >= logId {
+		if s.lastLogID == logId {
 			//slave has already owned this log
 			n++
+		} else if s.lastLogID > logId {
+			log.Error("invalid slave %s, lastlogid %d > %d", s.slaveListeningAddr, s.lastLogID, logId)
 		}
 	}
 
@@ -387,14 +398,10 @@ func (app *App) publishNewLog(l *rpl.Log) {
 	startTime := time.Now()
 	done := make(chan struct{}, 1)
 	go func(total int) {
-		n := 0
-		for {
+		for i := 0; i < total; i++ {
 			id := <-app.slaveSyncAck
-			if id >= logId {
-				n++
-				if n >= total {
-					break
-				}
+			if id < logId {
+				log.Info("some slave may close with last logid %d < %d", id, logId)
 			}
 		}
 		done <- struct{}{}