How can delegating method be so slow?

Question

I have few methods which are indicated as slow by profiler of jvisualvm

enter image description here

Unfortunately, I can't see what can be improved, since methods are

    public int getDimensionValue(int index) {
        if( !containsDimension(index) ) {
            throw new IndexOutOfBoundsException();
        }
        return delegate.getValue(index);
    }


    public boolean containsDimension(int index) {
        return delegate.contains(index);
    }

Suppose contains is really slow, but how can caller be slow too if it just call it?

Self time means time without time of callees or including it?

And what are the columns on the right hand side? My guess is that `containsDimension` has basically inlined `contains`... — Jon Skeet, Aug 05 '14 at 12:38

score 0 · Answer 1 · answered Aug 05 '14 at 12:40

0

Be careful when interpreting VisualVM's output: if you are looking at the "hot spots" list, you only see total time spent inside a method, regardless of call count. Now look at the actual call counts: they are quite huge numbers. So in your case, the method's aren't slow, they are just being called a lot. This does indicate that total performance would benefit most from those methods getting faster, but it doesn't say at all that the methods are slow. They may well be as fast as they can get, which means you already have an optimal program.

answered Aug 05 '14 at 12:40

William F. Jameson

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also the overhead of visualvm profiling may be substantial for small methods called a lot. – Thorbjørn Ravn Andersen Aug 05 '14 at 12:41
@ThorbjørnRavnAndersen That's what VisualVM's calibration on first run is for: it controls for its own overhead. Personally, I always go for the Sampler and find its results much more helpful. – Marko Topolnik Aug 05 '14 at 12:44
the calibration is only correct if the cpu-speed is unchanged – Thorbjørn Ravn Andersen Aug 05 '14 at 12:51
You can also repeat the calibration at any time in case of any doubts about changed CPU speed (highly unlikely, of course, especially when the CPU is under heavy load). – Marko Topolnik Aug 05 '14 at 12:57

How can delegating method be so slow?

1 Answers1