A while back a ticket was filed on the Rails tracker to turn on config.threadsafe! mode by default in production . Unfortunately, this change was met with some resistance. Rather than make resistance to change a negative thing, I would like to make it a positive thing by talking about exactly what config.threadsafe! does. My goal is to prove that enabling config.threadsafe! in multi threaded environments and multi process environments is beneficial, therefore the option can be removed.