title: MongoDB vs MySQL
body: <p>I used to build Ruby on Rails apps with MySQL.</p>
  
  <p>MongoDB currently become more and more famous and I am now starting to give it a try.</p>
  
  <p>The problem is, I don't know the underlying theory of how MongoDB is working (am using mongoid gem if it matter)</p>
  
  <p>So I would like to have a comparison on the performance between using MySQL+ActiveRecord and model generated by mongoid gem, could anyone help me to figure it out?</p>