How can I profile booting of a Rails application?

Question

Simple problem, I have a legacy Rails 2.3 application and it takes quite long to do anything. rake takes over 25 seconds, but it doesn't look like anything is really happening.

Is there any simple way I can just get some kind of profiler dump from the time when the app is loading, to see which methods take the longest time?

A solution for both Rails 2.3 and 3.1 would be even more helpful.

Answer 1

Profile a rake task that requires the rails environment, something like this:

 desc "Load it"
 task :loadit => :environment do

 end

then profile with ruby-prof

ruby -Ilib -S ruby-prof -p graph_html `which rake` loadit > profile.html

It ought to work with rails 2.3 have only tested it on 3.x but I see no reason why it should not work.

Answer 2

You could start your application with a profiler hooked in, e.g. ruby-prof or perftools.rb. While it's still starting up, launch a HTTP query against it, which would try go GET a /kill_me route as soon as the application starts. /kill_me could cause your application to gracefully die by calling exit. As a result you've got a profile of your startup.