I believe they went to Scala on the JVM
Why Use Scala?
Why use Scala when you have Ruby and Ruby on Rails? Well, we still use Rails. It works great for front-end stuff. The productivity is worth the tradeoff for working in a slower-performing dynamic language. When you think about what a web framework is doing under the hood, itÂs tons and tons of string concatenation. Ruby on Rails can handle that.
What we had a need for as Twitter grew was for long-running heavy processes, message-queuing, caching layers for doing 20,000 operations a second. Ruby garbage-collection is tough, Ruby doesnÂt do really well with long-running processes.
http://blog.redfin.c...r_uses_scala.html
Do some searches on Scala and Twitter. I agree with Scott, the servers must do a shared-nothing approach and they probably won't use the back-end of Rails ORM as much (ActiveRecord).
Have fun.
