The answer is in your heap: debugging a big memory increase in Ruby on Rails

I recently participated in an interesting series of debugging sessions tracking down the source of a large increase in memory when upgrading a Rails application. We ultimately tracked down the cause using John Hawthorn’s Sheap heap analyzer and successfully submitted a patch to Rails. I thought it was interesting enough to write up because maybe the general approach to debugging memory issues would be helpful (and this is the kind of stuff that I very quickly forget unless I write it down).