Profiling Rails¶

To profile a Rails application it is vital to run it using production like settings (cache classes, cache view lookups, etc.). Otherwise, Rail's dependency loading code will overwhelm any time spent in the application itself (our tests show that Rails dependency loading causes a roughly 6x slowdown). The best way to do this is create a new Rails environment, profile.rb.

To profile Rails:

Create a new profile.rb environment. Make sure to turn on cache_classes and cache_template_loading. Otherwise your profiling results will be overwhelmed by the time Rails spends loading required files. You should likely turn off caching.
Add the ruby-prof to your gemfile:

group :profile do
  gem 'ruby-prof'
end

Add the ruby prof rack adapter to your middleware stack. The Rails documentation describes several ways to do this. One way is to add the following code to application.rb:

if Rails.env.profile?
  config.middleware.use Rack::RubyProf, :path => './tmp/profile'
end

The path is where you want profiling results to be stored. By default the rack adapter will generate a html call graph report and flat text report.

Now make a request to your running server. New profiling information will be generated for each request. Note that each request will overwrite the profiling reports created by the previous request!