Does attaching a profiler cause some things to run slower then others?

Question

Is it possible that attaching a profiler to a JVM (let's say VisualVM) could make some methods run slower, while not effecting others and thus causing a skew in the results that makes it look like a certain piece of code is a hotspot when in fact it's not. I will ask specifically about reflection calls for an example. I'm running some code that shows a lot of time spent in Spring AOP calls (specifically invokeJoinpointUsingReflection) - which the author says runs fine in testing (using an in code microbenchmark) but when they profiled it showed this method to take longer then other non-reflection methods. (sorry if that' a little unclear) So it got my wondering if the profiler could really have this effect and lead a developer down a false trail. Feel free to answer with any examples, the reflection part is just my example.

Answer 1

Profilers regularly give mis-leading information, but in generally they are usually right. Where they tend to skew the result is in very simple methods which might be further optimised if profiling wasn't enabled.

If in doubt I suggest you use another profiler, such as YourKit (evalation version should be fine) It has more light weight recording, but can have the same issues.