There was a really good talk from Charles Nutter about making JRuby fast and the mutable things that Ruby does that basically break caching and things that you

There was a really good talk from Charles Nutter about making JRuby fast and the mutable things that Ruby does that basically break caching and things that you do to make things faster at runtime. I'm not surprised that persistent data structures can make things fast, in fact I've spent the last week speeding up a Rails app in some ugly spots by preloading the data structures to keep DB queries from happening, effectively turning a lot of just in time queries at the ORM level into a pre-loaded data graph. The speed is fantastic, but what is interesting is you could add a level of immutability to this and would be potentially even faster, especially on top of the JVM. I've been playing with the idea of immutable entities in Obvious Architecture for a while and it really changes the way you look at your business logic and performance.