It’s somewhat ironic that we heralded Rails 0.13 as being a great move forward for the performance of Rails and then half the threads on the mailing list is about “Rails is sLOOOW!”. We’ve found the problems, though.
The first was with the MySQL/Ruby bindings, which called GC.start whenever MySQL#free was called. And we just put in MySQL#free in 0.13 to improve things after each select of rows. This caused the garbage collector to run every time you selected something. Doh!
The C-bindings didn’t have this problem, so it wasn’t discovered by the core team right away, and that was posed as the solution on the mailing list. Unfortunately, it’s not necessarily trivial to compile native bindings on all platforms (notably Windows), so having fast Ruby bindings was indeed important. They’re fast again, but if you upgraded to the C-bindings you can be happy that you’re even faster.
The second problem was that we plugged a big memory leak in development mode, but doing so caused a total of 8 runs through the so-called ObjectSpace after each action (basically iterating over all objects in the interpreter 8 times, eeks!). On big applications this could take a while. On Basecamp it took 2 seconds. After the fix went in where we just traverse the ObjectSpace once, it’s down to a comfortable 0.2 seconds (which is about 0.17 faster than it even was before the memory leak fix!).
Thus, Rails 0.13.1 is near forth coming. As in this weekend. If you cannot wait, and we certainly won’t blame you, there are new beta gems that consist purely of bug fixes. Upgrade with
gem install rails --source http://gems.rubyonrails.org --include-dependencies.