By Jothy Rosenberg and Arthur Mateos
This article is taken from the book The Cloud at Your Service. The authors discuss the concept of sharding, a term invented by and a concept heavily employed by Google that is about how to partition databases so they scale infinitely. They show how Yahoo!, Flickr, Facebook, and many other sites that deal with huge user communities have been using this method of database partitioning to enable a good user experience concurrently with rapid growth.
Designing and Architecting for Internet Scale: Sharding (PDF)