title: So... this NoSQL thing
body: <p>I've been looking at MongoDB and I'm fascinated. It appears (although I have to be suspicious) that in exchange for organizing my database in a slightly different way, I get as much performance as I have CPUs and RAM for free? It seems elegant, and flexible, but I'm not trading that for fast like I am with Rails. So what's the catch? What does a relational database give me that I can't do as well or at all with Mongo? In other words, why (other than immaturity of existing NoSQL systems and resistence to change) doesn't the entire industry jump ship from MySQL? </p>
  
  <p>As I understood it, as you scale, you get MySQL to feed Memcache. Now it appears I can start with something equally performant from the beginning.</p>
  
  <p>I know I can't do transactions across relationships... when would this be a big deal?</p>
  
  <p>I read <a href="http://teddziuba.com/2010/03/i-cant-wait-for-nosql-to-die.html" rel="noreferrer">http://teddziuba.com/2010/03/i-cant-wait-for-nosql-to-die.html</a> but as I understand it, his argument is basically that real businesses which use real tools don't need to avoid SQL, so people who feel a need to ditch it are doing it wrong. But no "enterprise" has to deal with nearly as many concurrent users as Facebook or Google, so I don't really see his point. (Walmart has 1.8 million employees; Facebook has 300 million users).</p>
  
  <p>I'm genuinely curious about this... I promise I'm not trolling.</p>