queue_time_logger.rb

# combination of https://gist.github.com/daveyeu/4960893
# and https://gist.github.com/jasonrclark/d82a1ea7695daac0b9ee
class QueueTimeLogger
  attr_reader :app

  def initialize(app, options = {})
    @app = app
  end

  def call(env)
    now = Time.now.to_f

    # Delete Heroku's queue time header because it's incorrect and useless
    env.delete("HTTP_X_HEROKU_QUEUE_WAIT_TIME")

    microseconds = (now * 1_000_000).to_i
    env["HTTP_X_MIDDLEWARE_START"] = "t=#{microseconds}"

    if env["HTTP_X_REQUEST_START"]
      # HTTP_X_REQUEST_START is expected by New Relic to have a t= leading
      # but currently doesn't, so it can just get to_i applied.
      request_start_microseconds = env["HTTP_X_REQUEST_START"].to_i * 1_000
      queue_time_microseconds = microseconds - request_start_microseconds

      env["HTTP_X_QUEUE_TIME"] = "t=#{queue_time_microseconds}"
    end

    app.call(env)
  end
end

Hey all - check out https://github.com/RapGenius/heroku-true-relic, which is a gem version of this gist. We'll try to keep that up to date as we get more information about how best to track dyno-level queuing.

@dblock Thanks for the tip on not reporting negative queue time numbers; I incorporated that into the gem.

Thanks @a-warner but it was a totally unrelated issue (I had been trying out ruby 2.0.0 preview and switching back to 1.9.3 had broken the session cookie).

The gem looks great (I had started writing one myself but I'll give up on that now), thanks

do i need to modify my new relic or heroku configuration for the gem to work out of the box? i've just deployed this to a staging app I have running on the cedar stack with new relic standard, and am throwing a ton of requests at it with ab, but am seeing 0 queueing.