程序部署到BAE后报错Error: no open connections ,用了mogonskin

程序本地测试一切正常，部署到BAE后，用着用着，就报错Error: no open connections，

数据库链接文件db.js

var config = require('../config.js'),
    mongo = require('mongoskin');

var db = mongo.db(config.user+':'+config.pwd+'@'+config.host+':'+config.port+'/'+config.db,{safe:true})   

module.exports = db;

userModel

var mongo = require('./db.js');
userClass.getOne = function(user,cb) {
    mongo.collection('users').findOne(user,function (err,re) {
        cb(err,re);
    });
};

auto_reconnect=true后正常

var db = mongo.db(config.user+':'+config.pwd+'@'+config.host+':'+config.port+'/'+config.db+'?auto_reconnect=true',{safe:true})