Bryan has a couple of quick quick examples of using DTrace to go through some parts of a Rails application.

As one starts working more and more with web frameworks that depends on many pieces from other people, it’s pretty clear that being able to quickly and completely look at what your application is doing from the request all the way down to the kernel and networking stack is critical (look there’s even DTrace providers for PostgreSQL).

And this is done in production and in a non-interfering way.

Huge.

If you’re coming to one of the Scale With Rails workshops, expect to see plenty of this.