SAXON and exsl:node-set -- problem solved

Hi,

the problem is indeed in SAXON. And while exsl:node-set is not directly involved,
it is tightly coupled with rtf->node-set. Consider these two simple stylesheets:

it1.xsl
==========
  <xsl:template match="/">
    <xsl:apply-templates/>
  </xsl:template>

it2.xsl
===========
  <xsl:template match="/">
    <xsl:variable name="x">
    	<xsl:apply-templates/>
    </xsl:variable>
  </xsl:template>

Identity transformation by default is omitted for brevity. On a 500Kb file,
the first one runs 4 seconds with SAXON, the second one 33 seconds. Obviously,
the picture becomes only worse, with dependency roughly quadratic.

The cause of this dependency is in 

  com/icl/saxon/expr/FragmentValue.java

It's line 23 says:

    private Vector events = new Vector(20, 20);

which makes the container for the result-tree linearly expanding (that is, each time
the space is exhausted, new 20 elements are added to the vector, and the whole vector
is copied to the new Java array). The bigger the data is, the bigger amount has to
be copied for each twenty elements. 

Changing this line to:

    private Vectore events = new Vector(20); 

eliminates the problem, the vector will now occupy at most twice the place it would before
the change, but the time to expand it neglectible, so the two stylesheets complete in
the same time.

What concerns me is that a similar problem exists in jd.xslt 1.5.5. There is a cause
that forced the author of SAXON, a great program by all merits, to use linear increment
on this vector. Using exsl:node-set for chaining is incompatible with this decision,
and just fixing this problem may probably lead to others more severe.

What are these problems and is this fix suitable for SAXON?

David Tolpin
http://davidashen.net/




   


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