diff --git a/dht.go b/dht.go
index 45aec84..ff479e8 100644
--- a/dht.go
+++ b/dht.go
@@ -25,9 +25,14 @@ const (
 
 // Config represents the configure of dht.
 type Config struct {
-	K                    int
-	KBucketSize          int
-	Network              string
+	// in mainline dht, k = 8
+	K int
+	// for crawling mode, we put all nodes in one bucket, so KBucketSize may
+	// not be K
+	KBucketSize int
+	// candidates are udp, udp4, udp6
+	Network string
+	// format is `ip:port`
 	Address              string
 	PrimeNodes           []string
 	KBucketExpiredAfter  time.Duration
diff --git a/krpc.go b/krpc.go
index a87a25e..04af4ca 100644
--- a/krpc.go
+++ b/krpc.go
@@ -573,7 +573,9 @@ func handleRequest(dht *DHT, addr *net.UDPAddr,
 			port = addr.Port
 		}
 
-		dht.peersManager.Insert(infoHash, newPeer(addr.IP, port, token))
+		if dht.IsStandardMode() {
+			dht.peersManager.Insert(infoHash, newPeer(addr.IP, port, token))
+		}
 
 		send(dht.conn, addr, makeResponse(t, map[string]interface{}{
 			"id": dht.id(id),
diff --git a/peerwire.go b/peerwire.go
index 8ad3095..112c625 100644
--- a/peerwire.go
+++ b/peerwire.go
@@ -38,17 +38,12 @@ var handshakePrefix = []byte{
 }
 
 // read reads size-length bytes from conn to data.
-func read(conn *net.TCPConn, size int, data *bytes.Buffer) (err error) {
-	buffer := make([]byte, size)
-	if _, err = io.ReadFull(conn, buffer); err != nil {
-		return
-	}
-
-	n, err := data.Write(buffer)
-	if err != nil || n != size {
+func read(conn *net.TCPConn, size int, data *bytes.Buffer) error {
+	n, err := io.CopyN(data, conn, int64(size))
+	if err != nil || n != int64(size) {
 		return errors.New("read error")
 	}
-	return
+	return nil
 }
 
 // readMessage gets a message from the tcp connection.
@@ -215,11 +210,22 @@ func (wire *Wire) requestPieces(
 
 		sendMessage(conn, buffer[:length])
 	}
+	buffer = nil
 }
 
 // fetchMetadata fetchs medata info accroding to infohash from dht.
 func (wire *Wire) fetchMetadata(r Request) {
+	var (
+		length       int
+		msgType      byte
+		piecesNum    int
+		pieces       [][]byte
+		utMetadata   int
+		metadataSize int
+	)
+
 	defer func() {
+		pieces = nil
 		recover()
 	}()
 
@@ -245,15 +251,6 @@ func (wire *Wire) fetchMetadata(r Request) {
 		return
 	}
 
-	var (
-		length       int
-		msgType      byte
-		pieces       [][]byte
-		piecesNum    int
-		utMetadata   int
-		metadataSize int
-	)
-
 	for {
 		length, err = readMessage(conn, data)
 		if err != nil {
diff --git a/routingtable.go b/routingtable.go
index d582f3e..95a43de 100644
--- a/routingtable.go
+++ b/routingtable.go
@@ -119,7 +119,12 @@ func (pm *peersManager) Insert(infoHash string, peer *Peer) {
 	pm.Unlock()
 
 	v, _ := pm.table.Get(infoHash)
-	v.(*keyedDeque).Push(peer.CompactIPPortInfo(), peer)
+	queue := v.(*keyedDeque)
+
+	queue.Push(peer.CompactIPPortInfo(), peer)
+	if queue.Len() > pm.dht.K {
+		queue.Remove(queue.Front())
+	}
 }
 
 // GetPeers returns size-length peers who announces having infoHash.
@@ -326,6 +331,7 @@ type routingTable struct {
 	cachedNodes    *syncedMap
 	cachedKBuckets *keyedDeque
 	dht            *DHT
+	clearQueue     *syncedList
 }
 
 // newRoutingTable returns a new routingTable pointer.
@@ -339,6 +345,7 @@ func newRoutingTable(k int, dht *DHT) *routingTable {
 		cachedNodes:    newSyncedMap(),
 		cachedKBuckets: newKeyedDeque(),
 		dht:            dht,
+		clearQueue:     newSyncedList(),
 	}
 
 	rt.cachedKBuckets.Push(root.bucket.prefix.String(), root.bucket)
@@ -495,7 +502,6 @@ func (rt *routingTable) RemoveByAddr(address string) {
 // Fresh sends findNode to all nodes in the expired nodes.
 func (rt *routingTable) Fresh() {
 	now := time.Now()
-	queue := newSyncedList()
 
 	for e := range rt.cachedKBuckets.Iter() {
 		bucket := e.Value.(*kbucket)
@@ -507,13 +513,17 @@ func (rt *routingTable) Fresh() {
 		for e := range bucket.nodes.Iter() {
 			no := e.Value.(*node)
 			rt.dht.transactionManager.findNode(no, bucket.RandomChildID())
-			queue.PushBack(no)
+			rt.clearQueue.PushBack(no)
 		}
 	}
 
-	for e := range queue.Iter() {
-		rt.Remove(e.Value.(*node).id)
+	if rt.dht.IsCrawlMode() {
+		for e := range rt.clearQueue.Iter() {
+			rt.Remove(e.Value.(*node).id)
+		}
 	}
+
+	rt.clearQueue.Clear()
 }
 
 // Len returns the number of nodes in table.