Re: JDOM2 and Performance.

Hi

Performance testing on the Java VM is tricky.
To avoid getting caught out by cache-hot/cache-cold and JIT vs. not-JIT things, it's preferrable to do something like
this in PerfTest#timeRun(Runnnable)

// warm up the caches and get the JIT going
for (int i=0; i<10; i++) {
   runnable.run();
}

// give the JIT time to run, and get GC to run - GC can be stubborn sometimes
for (int i=0; i<3; i++) {
   Thread.sleep(100);
   System.gc();
}

// need 20 runs to get a decent average and standard deviation
ArithmeticMean mean = new ArithmeticMean(); // these two classes are in jakarata-commons-math
Variance deviation = new Variance();
for (int i=0; i<20; i++) {
  long time1 = System.currentTimeNanos();
  runnable.run();
  long time2 = System.currentTimeNanos();
  mean.increment(time2 - time1);
  deviation.increment(time2 - time1);
}

System.out.println("result  = " + mean.getMean() + " +- " + deviation.getVariance());

Regards, Noel Grandin

Rolf wrote:
> Hi all.
>
> I have put together a 'simple' system for measuring the relative performance of JDOM2. The idea is that I need to know
> whether I am improving or breaking JDOM performance as the code evolves.
>
> Currently the metric code is only useful of you compare apples to apples, and, in this case, it means processing a
> single (medium size) XML document on my laptop, yada-yada-yada. But, it should be useful as a tool to get a feel for
> what a code-change does.
>
> Already I can see that I probably have an issue in the SAXHandler (possibly an issue in JDOM-1.1.2 actually) because
> 1.1.2 is 5-times faster in that area than JDOM2.
>
> I have put together a results page here:
>
> http://hunterhacker.github.com/jdom/jdom2/performance.html
>
> It also describes what each test does. If you are interested in seeing the code and what it does have a look here (it
> is not well documented and it is still perhaps evolving):
>
> https://github.com/hunterhacker/jdom/commit/8b719c86913398ace8e197b6de145b33d9d300bb
>
>
> Rolf
> _______________________________________________
> To control your jdom-interest membership:
> http://www.jdom.org/mailman/options/jdom-interest/[email protected]
>

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