Finding Unused Production Code

Dan Mayer
LivingSocial (We're hiring)

How Dead Code Sticks Around

Large Teams aren't good at communicating what is no longer needed
AB tests, never removing a loser
Deprecation of old endpoints takes time
There are tests, but it is never used in prod

Finding Dead Code

Use Logs
Use NewRelic or Appneta (formerly Tracelytics)
Stats Instrumentation
Production Code Coverage
At LivingSocial using stats and Coverband, we have removed 10s of thousands of lines app of code.

Stats Instrumentation

ActiveSupport::Notifications.subscribe /render_partial.action_view|render_template.action_view/ do |name, start, finish, id, payload| 
  RenderTracker.track_template(name, start, finish, id, payload) unless name.include?('!') 
end

class RenderTracker
  
  def self.track_template(name, start, finish, id, payload)
    if file = payload[:identifier]
      Statsd.increment file
      Rails.logger.info "[RenderTracker] file: #{file}"
    end
    if layout = payload[:layout]
      Statsd.increment layout
      Rails.logger.info "[RenderTracker] layout: #{layout}"
    end
  end

end

Production Code Coverage: Coverband

Based on `set_trace_func`
It would be better to be based on `Coverage` but there is a bug in Ruby
(After talks @MWRC I might try to patch Ruby)
Performance Cost limited by Sampling
github.com/danmayer/coverband

Thanks

Dan Mayer
LivingSocial (We're hiring)