ruby script/plugin install http://newrelic.rubyforge.org/svn/newrelic_rpm

Our testing shows that this agent introduces minimal overhead: in production, a typical controller action will be impacted by less than 5 milliseconds in response time. (That's significantly less time than is typically spent in mapping a request to the appropriate controller action.) So, you can run RPM all the time, and always have access to the information you need to resolve performance problems and ensure your application can scale to meet the demands of your business.

The New Relic Agent runs in one of two modes:

DEVELOPER MODE
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Developer mode is on by default when you run your application in the development environment (but not when it runs in other environments.) When running in developer mode, the NewRelic Agent Rails Extension will track the performance of every http request serviced by your application, and store in memory this information for the last 100 http transactions.

When running in Developer Mode, the New Relic Agent will also add a few pages to your application that allow you to analyze this performance information. (Don't worry - those pages are not added to your application's routes when you run in production mode.)

To view this performance information, including detailed SQL statement analysis, go to http://localhost:3000/newrelic and start drilling down.

PRODUCTION MODE
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When your application runs in the production environment, the NewRelic agent runs in production mode. It connects to the New Relic RPM service and sends deep performance data to the RPM service for your analysis. To view this data, login to http://rpm.newrelic.com.

NOTE: you must have a valid account and license key to view this data online. When you sign up for an account at newrelic.com, you will be provided with a license key, as well as a default configuration file for NewRelic RPM. You can either paste your license key into your existing configuration file, config/newrelic.yml, or you can replace that config file with the one included in your welcome email.

Thank you, and may your application scale to infinity plus one.

There is currently no advanced documentation for this plugin.