title: What are the advantages of using a schema-free database like MongoDB compared to a relational database?
body: <p>I'm used to using relational databases like MySQL or PostgreSQL, and combined with MVC frameworks such as Symfony, RoR or Django, and I think it works great.</p>
  
  <p>But lately I've heard a lot about MongoDB which is a non-relational database, or, to quote the <a href="http://www.mongodb.org/display/DOCS/Home" rel="noreferrer">official definition</a>,</p>
  
  <blockquote>
    <p>a scalable, high-performance, open
    source, schema-free, document-oriented
    database.</p>
  </blockquote>
  
  <p>I'm really interested in being on edge and want to be aware of all the options I'll have for a next project and choose the best technologies out there.</p>
  
  <p>In which cases using MongoDB (or similar databases) is better than using a "classic" relational databases?
  And what are the advantages of MongoDB vs MySQL in general?
  Or at least, why is it so different?</p>
  
  <p>If you have pointers to documentation and/or examples, it would be of great help too.</p>