When discussing performance no opinion should be accepted without a metric

One of the great things about Rails is there is a plugin for just about everything and collecting performance metrics is no exception. Most of this is because of Ruby and it’s incredible meta-programming flexibility (but that’s another story). Rails has built-in support for some basic performance monitoring on the request stack (although in recent versions this has been extracted into a plugin), but there are some excellent alternatives.

RPM by NewRelic:

New Relic RPM is a Ruby on Rails performance monitoring application that lets you see and understand application performance metrics in real time so you can fix Rails problems fast. RPM is intuitive. It’s granular. And, it’s a 10-second Rails plug-in install.

metric_fu on GitHub:

metric_fu is a set of rake tasks that make it easy to generate metrics reports.  It uses Saikuro, Flog, Rcov, and Rails’ built-in stats task to create a series of reports.  It’s designed to integrate easily with CruiseControl.rb by placing files in the Custom Build Artifacts folder.

There are some great screencasts on Scaling Rails available from New Relic’s Rails Lab. And yes, scale is orthogonal to performance, but some of the discovery techniques are the same.

Updated:

A commenter has correctly pointed out that metric_fu is not a performance anaysis tool as such. I guess the subtext of what I am saying is that tools like these help track complexity – and complexity is often one of the underlying causes of performance issues.