diff --git a/sysmodule/mongomodule/mongomodule.go b/sysmodule/mongomodule/mongomodule.go
index 330ae5d..ba1864c 100644
--- a/sysmodule/mongomodule/mongomodule.go
+++ b/sysmodule/mongomodule/mongomodule.go
@@ -6,20 +6,49 @@ import (
 	"gopkg.in/mgo.v2/bson"
 	"sync"
 	"time"
-
+	"container/heap"
 	_ "gopkg.in/mgo.v2"
 )
 
 // session
 type Session struct {
 	*mgo.Session
+	ref   int
+	index int
+}
+
+type SessionHeap []*Session
+
+func (h SessionHeap) Len() int {
+	return len(h)
+}
+
+func (h SessionHeap) Less(i, j int) bool {
+	return h[i].ref < h[j].ref
+}
+
+func (h SessionHeap) Swap(i, j int) {
+	h[i], h[j] = h[j], h[i]
+	h[i].index = i
+	h[j].index = j
+}
+
+func (h *SessionHeap) Push(s interface{}) {
+	s.(*Session).index = len(*h)
+	*h = append(*h, s.(*Session))
+}
+
+func (h *SessionHeap) Pop() interface{} {
+	l := len(*h)
+	s := (*h)[l-1]
+	s.index = -1
+	*h = (*h)[:l-1]
+	return s
 }
 
 type DialContext struct {
 	sync.Mutex
-	sessions []*Session
-	sessionNum uint32
-	takeSessionIdx uint32
+	sessions SessionHeap
 }
 
 type MongoModule struct {
@@ -33,8 +62,12 @@ func (slf *MongoModule) Init(url string,sessionNum uint32,dialTimeout time.Durat
 	return err
 }
 
-func (slf *MongoModule) Take() *Session{
-	return slf.dailContext.Take()
+func (slf *MongoModule) Ref() *Session{
+	return slf.dailContext.Ref()
+}
+
+func (slf *MongoModule) UnRef(s *Session) {
+	slf.dailContext.UnRef(s)
 }
 
 // goroutine safe
@@ -48,6 +81,7 @@ func dialWithTimeout(url string, sessionNum uint32, dialTimeout time.Duration, t
 	if err != nil {
 		return nil, err
 	}
+
 	s.SetMode(mgo.Strong,true)
 	s.SetSyncTimeout(timeout)
 	s.SetSocketTimeout(timeout)
@@ -55,13 +89,12 @@ func dialWithTimeout(url string, sessionNum uint32, dialTimeout time.Duration, t
 	c := new(DialContext)
 
 	// sessions
-	c.sessions = make([]*Session, sessionNum)
-	c.sessions[0] = &Session{s}
-	for i:=uint32(1) ;i< sessionNum;i++{
-		c.sessions[i] = &Session{s.New()}
+	c.sessions = make(SessionHeap, sessionNum)
+	c.sessions[0] = &Session{s, 0, 0}
+	for i := 1; i < int(sessionNum); i++ {
+		c.sessions[i] = &Session{s.New(), 0, i}
 	}
-
-	c.sessionNum = sessionNum
+	heap.Init(&c.sessions)
 
 	return c, nil
 }
@@ -75,15 +108,32 @@ func (c *DialContext) Close() {
 	c.Unlock()
 }
 
-func (c *DialContext) Take()*Session{
+// goroutine safe
+func (c *DialContext) Ref() *Session {
 	c.Lock()
-	idx := c.takeSessionIdx %c.sessionNum
-	c.takeSessionIdx++
+	s := c.sessions[0]
+	if s.ref == 0 {
+		s.Refresh()
+	}
+	s.ref++
+	heap.Fix(&c.sessions, 0)
 	c.Unlock()
 
-	return c.sessions[idx]
+	return s
 }
 
+// goroutine safe
+func (c *DialContext) UnRef(s *Session) {
+	if s == nil {
+		return
+	}
+	c.Lock()
+	s.ref--
+	heap.Fix(&c.sessions, s.index)
+	c.Unlock()
+}
+
+
 // goroutine safe
 func (s *Session) EnsureCounter(db string, collection string, id string) error {
 	err := s.DB(db).C(collection).Insert(bson.M{