使用 session-mongodb 存储session 时，默认会产生5条数据库链接

Mon Jul 01 15:43:50.377 [initandlisten] connection accepted from 127.0.0.1:37821
 #1 (1 connection now open)
Mon Jul 01 15:43:50.385 [initandlisten] connection accepted from 127.0.0.1:37822
 #2 (2 connections now open)
Mon Jul 01 15:43:50.385 [initandlisten] connection accepted from 127.0.0.1:37823
 #3 (3 connections now open)
Mon Jul 01 15:43:50.385 [initandlisten] connection accepted from 127.0.0.1:37824
 #4 (4 connections now open)
Mon Jul 01 15:43:50.393 [initandlisten] connection accepted from 127.0.0.1:37825
 #5 (5 connections now open)
Mon Jul 01 15:44:05.612 [initandlisten] connection accepted from 127.0.0.1:37828
 #6 (6 connections now open)
Mon Jul 01 15:44:05.627 [conn6] end connection 127.0.0.1:37828 (5 connections no
w open)

其实应该是一条链接的，应该怎么做啊 app.js配置

var MongoStore = require('session-mongoose')(express);
var settings = require('./Settings');
var sessionStore = new MongoStore({
  db:settings.db
},function(){
  console.log('connect mongodb success...');
});
app.use(express.session({
    secret:settings.db,
    store:sessionStore,
    cookie:{
      maxAge:new Date(Date.now()+1000*60*60)
    }
}));