Capacity Planning & bottlenecks


I’m looking at bringing in new a site online at the end of next month.

My site will be a typical e-commerce site. Lots of people browsing
products in a database, a smaller number registering & purchasing. The
purchasing process will require authorisation from a 3rd party credit
card transaction provider via SSL requests.

I want to do some basic capacity planning & so far I’ve got OS
performance scripts that grab the CPU, RAM, & disk utilisation of my
servers machine every 5 mins. I can graph the output of these & see
roughly how my hardware is travelling

I’ve also got application performance counters in the important bits of
my code. These spit out start & stop times of various parts of
processes. This way I can quickly identify any slows downs and/or trends
in the application performance. However, this won’t tell me why the
trends are occuring.

Hence, I want to get a little bit more sophisticated with my OS
performance scripts & tune these towards a rails environment. It would
be great if I could get some feedback on what are the typical
bottlenecks in rails apps, how they were identified, & how they were

Thanks for any help.