http://www.facebook.com/note.php?note_id=23844338919

I joined Facebook in April 2007 and, after getting settled over the course of a few weeks, my manager Robert Johnson approached me. We talked for a while but the conversation boiled down to:

Bobby: “So, Jason, we’re going to open a new datacenter in Virginia by 2008. Do you think you can help?”
Me: “Uh…. yes?”
Bobby: “Great!”

This article explains 1) how to implement caching correctly and 2) how to route user request to proper database in master-slave database env.