mongodb的MongoClinet是已经内置连接池了的，可以通过poolSize修改配置，至于获取连接实例，只需要用nodejs维持一个单例就可以了：
var MongoClient = require('mongodb').MongoClient;
var url = 'mongodb://localhost:27017/shop'
var option = {
reconnectTries: 3,
auto_reconnect: true,
poolSize : 40,
connectTimeoutMS: 500,
useNewUrlParser: true
};
function MongoPool(){}
var p_db;
function initPool(cb){
MongoClient.connect(url, option, function(err, db) {
if (err) throw err;
p_db = db;
if(cb && typeof(cb) == 'function')
cb(p_db);
});
return MongoPool;
}
MongoPool.initPool = initPool;
function getInstance(cb){
if(!p_db){
initPool(cb)
}
else{
if(cb && typeof(cb) == 'function')
cb(p_db);
}
}
MongoPool.getInstance = getInstance;
module.exports = MongoPool;
调用时：
var MongoClient = require('mongodb').MongoClient
var app = require('express')()
var MongoPool = require('./db/dbPool.js')
app.listen(3000, function() {
MongoPool.initPool()
console.log('serve start successfully on the port: 3000')
})
app.get("/", function(req, res) {
MongoPool.getInstance(function (client){
var db = client.db('shop')
db.collection('user').find({}).toArray(function(err, result) {
res.end(JSON.stringify(result))
})
});
});
