Today our partner, New Relic, released an update to the Ruby New Relic agent that addresses issues brought up by our customers. The new version corrects how New Relic reports performance metrics for applications running on Heroku. Queueing time is now reported as the total time from when a request enters the router until the application starts processing it. Previous versions of New Relic only reported queueing time in the router. The new approach will result in more accurate queueing metrics that allow you to better understand and tune the performance of your application.
Update, Feb 22:
New Relic has released a similar update for Python. Python developers should update to this latest version to benefit from the improved metrics. JVM language developers do not need to take any action. The current New Relic Java agent already includes the improved queue time metrics.
Install or update the New Relic Ruby Add-on
If you are already using New Relic with your Ruby apps, then simply update your Gemfile to reference the new agent version:
gem "newrelic_rpm", "~> 3.5.7.59"
then run
$ bundle update newrelic_rpm
$ git add Gemfile Gemfile.lock
$ git commit -m 'update new relic agent'
$ git push heroku master
If you are not yet using New Relic, you can learn how to install and configure the add-on on Dev Center.
How It Works
The updated New Relic agent uses an improved strategy for reporting request queue times on Heroku. Prior to this update, New Relic reported request queue time using a value set by the Heroku routing mesh. This only reflected the time a request spent in the router queue and did not properly include time spent waiting in the dyno’s request queue.
Our routing performance update documents our finding that some applications have requests that may spend significant time queued on dynos. To help our customers understand precisely where their applications are being delayed, the updated New Relic agent includes dyno wait time in the total queue time metric. The new queue time is calculated as the difference between the time the Heroku router first gets a request and the time the request begins processing on the dyno. The result is a more accurate picture of how long requests wait in queues.
Clock Skew
The new version of New Relic calculates queue times using two different clocks — the dyno and router clocks. While Heroku servers regularly sync their clocks, it’s common for clocks to drift apart between syncs. This phenomenon is known as clock skew and it can affect the queue time metric collected by New Relic. In our experience, even though clock skew can cause small inaccuracies, the overall trend data displayed by New Relic will still accurately reflect your application’s queue times.
How to Learn More
If you’d like more information on how to install and configure the New Relic add-on, please see the New Relic Dev Center article and the Unicorn specific instructions. For general suggestions on how to improve the performance of your app, check out our performance overview page.