The MRI 2.2 garbage collector has gaines some significant improvements over its predecessors. There is now much more to tune and optimize for. The default settings are rarely optimal for an app, however, and gaining knowledge of the settings is a pita.

In Rails Garbage Collection: Tuning Approaches, Lourens takes you in to the deep end of the GC pool and tells you how you can get optimal GC settings for your app – in a fully automated manner.