APC exists because PHP reloaded source files each time a script was executed through your webserver. No such parallel exists in Ruby; once source files are load

APC exists because PHP reloaded source files each time a script was executed through your webserver. No such parallel exists in Ruby; once source files are loaded in a process, they stay loaded for that process. In theory it might allow for faster loading of Ruby code (more analogous to Python's .pyc files), but IIRC early experiments (in the early 2.0 days) showed it to be counterproductive in many cases.