I have several Drupal sites with which I'm using New Relic to help monitor and debug performance issues.
I've been finding that when viewing the "Web Transactions" section under "Monitoring", that a large percentage of time is spent in "/theme". When I click in to view a trace, then view the Trace details, I often find that the majority of the time is listed in a rows named "Application Code (in /theme)".
The help link beside "Application Code (in /theme)" takes me to New Relic's PHP Custom Metrics Collection page. The documentation is clear enough, but what I don't understand is how to make this useful in Drupal. I'm guessing this is difficult for me because of Drupal's hook system, and (again guessing) that the "Application Code" that New Relic is referring to in this case are calls to theme() functions.
Is there something that I can do to get more useful information out of New Relic? First thing that comes to mind is "killing a kitten" and hacking core's theme() function to insert a New Relic Custom Metric, but I'd prefer not to do that (nor do I know for certain it will help!).