How do I get a more detailed transaction trace with the Ruby New Relic agent

Question

I'm running a rails 3.0 application on Heroku and using the New Relic addon/service.

I have been looking at the transaction traces feature (available in the pro version) to understand a little more about the performance characteristics of the application. However, a significant portion of time (30-50%) is "uninstrumented time". After making a few stabs by putting method_tracers in some places and going through the reasonably slow cycle to test whether I get more info, I'm feeling this is going nowhere fast.

It seems in the PHP new relic agent they have a great feature to get very detailed traces without needing to guess where to put method tracers: http://newrelic.com/docs/php/php-agent-faq#top100

Is there anything similar to this for ruby?

Note: I'm already using rpm_contrib to get some more info and have garbage collection stats enabled. Also, this is not about fixing a performance problem, just understanding how to better use the performance tools available and scratch a niggling itch about that uninstrumented time.

Answer 1

There isn't currently anything similar for Ruby. I'll mention it to the Ruby engineer when I get a chance. My guess is unless a lot of requests come in for it, it won't be at the top of the list for a while, though. In the meantime, you can use the method tracers to figure out the uninstrumented time.

Hope that helps.

Answer 2

Method tracers can work well, but if you have a lot of code in your controller, try a binary search using trace_execution_scoped, which records the time spent in a block of code:

http://newrelic.github.com/rpm/NewRelic/Agent/MethodTracer/InstanceMethods/TraceExecutionScoped.html#method-i-trace_execution_scoped

Add a couple calls to this, give each metric a sensible name like "Custom/MySlowControllerAction/block0" (first argument to trace_execution_scoped), and repeat.

The metrics you name will show up not just in Transaction Traces, but also in the Performance Breakdown for the controller action under the Web Transactions tab, so you'll see average time in that block of code across all requests, not just the slow ones.