XOM API for Processing XML with Java

[Elliotte Harold <elharo AT metalab.unc.edu>]

Wolfgang Hoschek wrote:


> It would help to know on which VM/OS you ran the tests. My experience is 
> that client VMs can easily be a factory 5 slower for XOM apps. JDK 1.5 
> server VM is fastest, unsurprisingly. It is also significantly faster 
> than 1.4.2 server VM. MacOSX does not have a server VM and is far from a 
> throughput environment (even though a very nice development 
> environment). I run benchmarks on Linux JDK 1.5 server VM, even though I 
> develop mostly on MacOSX.

I just ran them on Mac OS X 10.3 with Java 1.4. If we really are at a 
point where swapping the VM and platform makes that big a difference, 
then I'm not sure how much optimization I should do. It's way too easy 
to tie things to closely to one architecture.

> Profiling tools other than '-server  
> -agentlib:hprof=cpu=samples,depth=10' on JDK 1.5 tend to greatly perturb 
> results, sometime to the point of making them meaningless. See 
> http://java.sun.com/developer/technicalArticles/Programming/HPROF.html
>
> > toCharArray instead of charAt
>
>
> is the wrong strategic direction based on my PCDATA tests. the better 
> the compiler, the more charAt and its checks can be optimized away, and 
> the more the toCharArray memory copy degrades performance (and memory 
> locality). As I said my PCDATA tests were on JDK 1.5 server VM, Linux.

toCharArray() does worry me a bit, and I've been careful to test it 
before using it, but when I've profiled it on Mac OS X and Linux with 
Java 1.4 it does make a difference.

> As I mentioned in a previous mail, microbenchmarks such as your may give 
> unrealistic results. Care to repeat tests with the BinaryXMLTest?

It seems more fruitful to benchmark based on standard XOM rather than 
the NUX fork. The test I devised is basically the same thing as your 
test, except that I load up a real XML document first instead of a BNUX 
document, but then I proceed to create a copy of that document by 
calling constructors, appendChild, addAttribute, etc. so it's a pretty 
good simulation of creating a whole document from scratch in memory 
without any of the back doors the copy methods and the Builder use. See

https://xom.dev.java.net/source/browse/xom/src/nu/xom/benchmarks/Reproducer.java?rev=1.1&content-type=text/vnd.viewcvs-markup

--
Elliotte Rusty Harold  elharo AT metalab.unc.edu
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