Measure, don’t guess. by Eduardo Bellani
… when you trade safety for performance, you may get neither. Especially when it comes to concurrency, the intuition of many developers about where a performance problem lies or which approach will be faster or more scalable is often incorrect.
It is therefore imperative that any performance tuning exercise be accompanied by concrete performance requirements (so you know both when to tune and when to stop tuning) and with a measurement program in place using a realistic configuration and load profile.
Measure again after tuning to verify that you’ve achieved the desired improvements. The safety and maintenance risks associated with many optimizations are bad enough—you don’t want to pay these costs if you don’t need to—and you definitely don’t want to pay them if you don’t even get the desired benefit. (Goetz 2006)