Why is MySQL in Node.js so slow?

My Node.js Code is like below

CODE1: below

var http=require('http');
var MySQL = require('mysql');

mysql = MySQL.createConnection(...)

http.createServer(function(req, res){
    // the query will take several seconds
    mysql.query("SELECT SLEEP(1)", function....)
});
http.listen(...);

The problem is the server will be crash when I refresh the page too fast. I think is the node-mysql module's problem, it process the query in a queue.So I try to create a connection pool.

CODE2: below

....
var pool = require('generic-pool');
var mp   = pool.Pool({
    ...
    create: function(cb){
        client = MySQL.createConnection(...);
        cb(null, client)
    },
    max: 10, // up to 10 connection
    min: 2,
    ...
});
....
    mp.acquire(function(err, mysql){

        // the query will take several seconds
        mysql.query("SELECT SLEEP(1)", function....)
        mp.release(mysql);
    });
....

But the problem still here, Why? How can I fix this.

EDIT: I launch 100 requests with 100 concurrency, 10 seconds expected. But it take 20 seconds. Why? Is The pool only support up to 5 connection?