gistfile1.js

/**
 * Created with JetBrains WebStorm.
 * User: artem
 * Date: 10.01.13
 * Time: 21:34
 * To change this template use File | Settings | File Templates.
 */
var mysql = require('mysql'),
  Promise = require("promise").Promise;

var Server = function (user, pass, host) {
  this._conn = mysql.createConnection({
    host: host,
    user: user,
    password: pass
  });
  this.queue = [];
};

Server.prototype.query = function (query, params, callback) {
  var qid = Math.random(),
    queue = this.queue;
  queue.push(qid);
  this._conn.query(query, params, function (err, rows, fields) {
    queue.splice(queue.indexOf(qid), 1);
    callback(err, rows, fields);
  })
};

//Test data
var master = new Server('root', '', 'localhost'),
  slaves = [
    new Server('root', '', 'localhost'),
    new Server('root', '', 'localhost'),
    new Server('root', '', 'localhost'),
    new Server('root', '', 'localhost')
  ];

/**
 * Select less loaded server
 * @return {Server}
 */
var getFreeServer = function () {
  var minInd = 0;
  for (var i = 0; i < slaves.length; i++) {
    if (slaves[i].queue.length === 0) {
      return slaves[i];
    }
    if (slaves[i].queue.length < slaves[minInd].queue.length) {
      minInd = i;
    }
  }
  return slaves[minInd];
};

module.exports = {
  select: function (query, params) {
    var promise = new Promise(),
      server = getFreeServer();

    server.query(query, params, function (err, result) {
      if (err) promise.errback(err);
      promise.resolve(result);
    });
    return promise;
  },
  del: function (query, params) {
    var promise = new Promise();
    master.query(query, params, function (err, result) {
      if (err) promise.errback(err);
      promise.resolve(result);
    });
    return promise;
  },
  update: function (query, params) {
    var promise = new Promise();
    master.query(query, params, function (err, result) {
      if (err) promise.errback(err);
      promise.resolve(result);
    });
    return promise;
  },
  create: function (query, params) {
    var promise = new Promise();
    master.query(query, params, function (err, result) {
      if (err) promise.errback(err);
      promise.resolve(result);
    });
    return promise;
  },
  masterQuery: function (query, params) {
    var promise = new Promise();
    master.query(query, params, function (err, result) {
      if (err) promise.errback(err);
      promise.resolve(result);
    });
    return promise;
  }
};