> On Nov 26, 2017, at 2:17 PM, Matthew Broadhead 
> <matthew.broadh...@nbmlaw.co.uk> wrote:
> So to run the tests I could reverse the changes of the commit and then update 
> to javax.xml.* and run tests?
> I am still struggling a bit to understand exactly what is happening wrt 
> VariableStack and how I can change over to XPathVariableResolver.  And also 
> don't see a way to replace XBoolean, XNumber, XString etc...
> I will keep trying things.   Can I come back to you with specific queries?

I did experiment with a pure JAXP based solution - there’s a patch 
<https://bz.apache.org/bugzilla/attachment.cgi?id=26445&action=diff> attached 
to #27717 that might be a place to start from. You may need to roll back a bit 
to get it to apply. 

From what I remember, the performance problem stemmed from the evaluation of 
XPath inside the loop, with both Xalan and JAXP (which used a shaded version of 
Xalan) reinitializing the DTM each time leading to N * N scaling. The fix was 
to use Xalan’s API directly to convert the document’s DOM to a DTM once and 
then apply the XPath against the DTM each time leading to 1 * N scaling. 

The downside is that there was a direct dependency on Xalan 2.7.1. I think we 
tried using 2.7.2 but there was some other problem with that I can’t find at 
the moment. Given the stability of Xalan/Xerces, what’s causing the conflict 
with FOP?

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