[jdom-interest] JAXP performance problems

[Jimmy Zhang]

Why would factory instantiation be so expensive???
It doesn't make sense...
----- Original Message ----- 
From: "Tatu Saloranta" <cowtowncoder at yahoo.com>
To: <jdom-interest at jdom.org>
Sent: Friday, September 15, 2006 4:02 PM
Subject: Re: [jdom-interest] JAXP performance problems


> --- "Klotz, Leigh" <Leigh.Klotz at xerox.com> wrote:
> 
>> I've recently found two JAXP performance problems. 
>> I've filed a bug
>> with Sun on them.
> 
> I was under impression that these were somewhat
> well-known (and quite severe) problems. It has been
> discussed on various mailing lists earlier (SAX, StAX
> at least). ;-/
> 
> Unfortunately I think there is little that can be done
> to fix the process of factory discovery, as specified:
> changes that would improve performance would by
> necessity have to change behavior. This because the
> expensive part (that of discovering services files
> using class loader) is inherently dynamic: and caching
> based on class-loader would be tricky.
> So I wouldn't count on Sun fixing it any time soon --
> it's not easy to fix.
> 
> So how do I know this? I investigated the problem in
> relation to Stax implementations... it's quite
> expensive to do factory.newInstance() call, anywhere
> from 5 milliseconds up (for some web app containers
> probably much higher than that). While it's possible
> to cache results of the first 2 methods (system prop,
> jaxp.properties file read), those are not the main
> problem... and caching last one would have to be on
> per-classloader basis, without having hard reference
> to class loader. Perhaps if class loader object
> supported caching of discovery mechanism, this could
> be done.
> 
> This is something users have to be aware of:
> preferably by reusing factories, or if not, using a
> workaround:
> 
> (a) Setting the system property that is used to find
> the factory class. Accessing this is relatively cheap.
> (b) Using the actual implementation factory directly,
> using a app-specific property: while this removes the
> complete implementation independency, it should be
> easy to wire things using Springs or such.
> 
> -+ Tatu +-
> 
> 
> 
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