A couple of years ago, a client asked me to build a recommendation engine for them. Coming into this with a minimal knowledge of statistical math, I ultimately built a relatively simple recommendation engine in Ruby. The design made heavy use of Redis Sets, Lists, and Hashes in order to greatly reduce the number of SQL queries to provide recommendations. This talk will be a case study discussing the object-oriented considerations in designing a scalable service, how Redis was a good fit for the project, and some of the painful lessons that I learned along the way so that you don't have to repeat them.