var pool  = mysql.createPool({
    connectionLimit : 10,
    database: '',
    host: '127.0.0.1',
    user: '',
    password: ''
});

function query(sql, callback) {
    console.log(sql);
    if (typeof callback === 'undefined') {
        callback = function() {};
    }
    pool.getConnection(function(err, connection) {
        if(err){
            // return callback(err);
            query(sql, callback);
            return;
        }
        connection.query(sql, function(err, rows) {
            if(err){
                // return callback(err);
                query(sql, callback);
                return;
            }
            connection.release();
            return callback(null, rows);
        });
    });
}