CODEWITHSUNDEEP
javaperformancereflectionprofiling
Gandalf
Gandalf

Reputation: 9855

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

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.

Upvotes: 3

Views: 168

Answers (4)

trashgod
trashgod

Reputation: 205795

Certain profilers require a calibration step, e.g. NetBeans and VisualVM. You might verify the vintage and settings for your chosen profiler.

Upvotes: 0

Peter Lawrey
Peter Lawrey

Reputation: 533530

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.

Upvotes: 3

Ira Baxter
Ira Baxter

Reputation: 95352

Heisenberg famously observed that collecting information from a system always disturbs it, so you can't get an undisturbed observation. (Thus the software term, "Heisenbug"). Yes, collecting profiling information can cause the actual performance to be changed in ways that will misdirect you.

Whether that is true in a significant way for your particular JVM or profiler, and how much disturbance occurs, is a matter of engineering.

Upvotes: 3

Amir Afghani
Amir Afghani

Reputation: 38541

Most profilers are sample based, and thus the more data you collect, the more accurate the results are. As far as I know, there is no bias for or against methods written purely in Java.

Upvotes: 0

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