Rails3.2 performance: slower?

Some people have done Rails2 from medium-sized to large-scale webapps.

Has someone upgraded Rails 2-3-4 from medium-sized to large-scale webapps? I am eager to hear about your experience. When Google searches for "Rails performance", there are only a few results, which always gives me more details about the upgrade experience of other developers. (1) Just like using dynamic streams on compatible web servers, in some cases

Has someone upgraded Rails 2-> 3-> 4 from medium-sized to large-scale webapps? I am eager to hear about your experience. When Google searches for "Rails performance", there are only a few results, which always gives me more details about the upgrade experience of other developers.

(1) Just like using dynamic streams on compatible web servers, new cache models can also improve performance in some cases. Because the purpose of this article is to focus on "performance", and performance belongs to the scope of Dynamic web applications running on servers, this means (we are concerned with) such as interpreting requests, interact with the database and present a response.