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

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.