If you have a Java application that is consuming CPU when it isn't doing anything, how do you determine what it is doing?

Question

I am calling a vendor\'s Java API, and on some servers it appears that the JVM goes into a low priority polling loop after logging into the API (CPU at 100% usage). The sam

Answer 1

Use a profiler. Yes they cost money, and using them can occasionally be a bit awkward, but they do provide you with a great deal more real evidence rather than guesswork.

Human beings are universally bad at guessing where performance bottlenecks are. It just seems to be something our brains aren't build to do very well. It may seem obvious, you may have great ideas about what the problem is, but the real world often turns out to be doing something different. And optimising the wrong part of code means, at best, lots of work for minimal benefit. More often it makes things slower, and sometimes it breaks things entirely. So before you make any changes for the sake of optimisation, you should always have real evidence from a profiler or other accurate tool.

As mentioned, both JProfiler and YourKit are both fairly good and not prohibitively expensive. Last time I looked, they both had free demos too.