Why I Hate Ruby

Ruby's garbage collector is garbage. There are many tips online for improving Ruby on Rails (RoR) performance by patching the stock garbage collector and compiling your own ruby interpreter. This is a pain in the ass if you are managing a bunch of boxes.

One method to help things that I applied at work recently was adding this to my app/controllers/application_controller.rb file. I got an improvement in execution time of a particularly tough action from about 750 ms down to 200 ms using this technique. With that said, I felt very dirty applying it. It is definitely a "Rob Peter to pay Paul" moment and I wonder where the time I robbed is going to come back and and bite me in the ass.

class ApplicationController
  around_filter :no_gc
  def no_gc
    GC.disable
    begin
      yield
    ensure
      GC.enable
    end
  end
end

I don't recommend this in practice. I have a feeling the app will suffer performance burps every once in a while as accumulated garbage is collected every N requests. But so far, it seems to be working in a staging environment. Time will tell ...

9/18/2009: Rather than hack around to disguise a problem, analyze the reason for the problem ...

After modifying the above around filter as follows ...

class ApplicationController
  around_filter :no_gc
  def no_gc
    GC.disable
    begin
      start_count = ObjectSpace.each_object {}
      yield
      end_count = ObjectSpace.each_object {}
      logger.info("OBJECTS CREATED = #{end_count - start_count}")
    ensure
      GC.enable
    end
  end
end

I have determined that the action I am profiling is creating a boatload of objects (89K+ per request!!). No wonder we are having GC issues. By turning off the garbage collector, we put a temporary band aid on a real problem. My initial instincts about this solution were correct: it smells. We still haven't figured out where all the object creations are coming from, but now that we know what to look for, it shouldn't be too hard to find them.