XOM API for Processing XML with Java

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

Wolfgang Hoschek wrote:
> Allow me to speculate that the xom source snippet below might have to do 
> with the just mentioned profiler and/or client VM problems, or similar 
> reasons:

This comment goes back to when I was developing on Linux, not the Mac. 
If you could demonstrate conclusively that this was a problem, I'd 
consider revisiting it. However. these sorts of low-level optimizations 
really do run the risk of hurting more than they help. Even if they work 
today on one particular VM with one batch of test documents, that can 
turn completely around on another VM processing documents with different 
characteristics.

Algorithm-level optimizations like caching the namespace URIs and 
short-circuiting the scheme checking for http seem a lot more reliable 
and effective. I'm not sure how many more of these there are to be found 
though. Possibly we could cache element names as well, but that would 
need a much bigger cache and a lot more search time than namespace URIs, 
so it might well not help. Possibly I could cache namespace prefixes 
separately. Those tend to repeat, and not to be excessively numerous so 
there shouldn't be too much cache thrashing. That might help documents 
that use namespace prefixes. I'll put that on my TODO list.

Another reason I don't want to be too aggressive here is simply that 
this is not where most applications spend most of their time. Almost 
every real world application I've seen is limited by one or more of 
three things:

1. Input, including parsing.
2. Output, including serialization
3. Non-XML operations like encryption and decryption

NUX is a little unusual here because it does its own parsing and 
serialization; but I still suspect in practice a lot of time will get 
spent in raw I/O. There's a good reason most XML benchmarks precache 
documents in memory to0 avoid I/O costs. If they didn't, I/O would swamp 
everything they're trying to measure. Even if we succeeded in reducing 
in-memory operations to zero, I'm afraid it wouldn't have much effect on 
most applications. :-(

--
Elliotte Rusty Harold  elharo AT metalab.unc.edu
XML in a Nutshell 3rd Edition Just Published!
http://www.cafeconleche.org/books/xian3/
http://www.amazon.com/exec/obidos/ISBN=0596007647/cafeaulaitA/ref=nosim