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RE: Comparing grouping techniques in terms of performance

2004-04-06 10:27:03
You seem to have varied several things between the two stylesheets. One of
them uses for-each, another uses apply-templates; one uses the generate-id()
approach to compare node identity, the other uses the count($X|.) technique;
one adds more output; one does sorting. The golden rule with performance
comparisons is to only change one variable at a time. And then you need to
repeat the measurements with a different XSLT processor to see whether the
results are similar.

Michael Kay 

-----Original Message-----
From: Pieter Reint Siegers Kort 
[mailto:pieter(_dot_)siegers(_at_)elnorte(_dot_)com] 
Sent: 06 April 2004 16:43
To: xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com
Subject: [xsl] Comparing grouping techniques in terms of performance

Hi all,
 
looking at various requests in the list regarding grouping, 
especially the
Muenchian Method, explained very well by Jeni at
 http://www.jenitennison.com/xslt/grouping/muenchian.html, and another
method I regularly have seen before, that uses 
template processing rather than the <for-each> approach (see 
below),  I
wanted to see how the two methods compare in 
terms of performance.
 
So, suppose I have the same input that Jeni uses, but making 
it a bigger XML
file (about 2000 entries):
 
<records>
 <contact id="0001">
  <title>Mr</title>
  <forename>John</forename>
  <surname>Smith</surname>
 </contact>
 <contact id="0002">
  <title>Dr</title>
  <forename>Amy</forename>
  <surname>Jones</surname>
 </contact>
 <contact id="0002">
  <title>Mr</title>
  <forename>Brian</forename>
  <surname>Jones</surname>
 </contact>
 <contact id="0002">
  <title>Ms</title>
  <forename>Fiona</forename>
  <surname>Smith</surname>
 </contact>
... repeating the above block ...
</records>

 
Using the <for-each> approach on my machine [Dell GX-240, Win2003,
XSelerator 2.6, MSXML 4.0], like this:
 
<xsl:transform xmlns:xsl="http://www.w3.org/1999/XSL/Transform
<http://www.w3.org/1999/XSL/Transform> " version="1.0">
 
<xsl:key name="contacts-by-surname" match="contact" use="surname" />
 
<xsl:key name="contacts-by-surname" match="contact" use="surname" />
<xsl:template match="records">
 <xsl:for-each select="contact[count(. | key('contacts-by-surname',
surname)[1]) = 1]">
  <xsl:sort select="surname" />
  <xsl:value-of select="surname" />,<br />
  <xsl:for-each select="key('contacts-by-surname', surname)">
   <xsl:sort select="forename" />
   <xsl:value-of select="forename" /> (<xsl:value-of 
select="title" />)<br
/>
  </xsl:for-each>
 </xsl:for-each>
</xsl:template>
 
</xsl:transform>
 
showed that the transformation took up about 750 msec.
 
Then, using the template approach (adding just a bit of 
HTML), as follows:
 
<xsl:transform xmlns:xsl="http://www.w3.org/1999/XSL/Transform
<http://www.w3.org/1999/XSL/Transform> " version="1.0">
 
<xsl:key name="contacts-by-surname" match="contact" use="surname" />
 
<xsl:template match="records">
   <html>
     <body>
         <xsl:apply-templates select="contact[generate-id() =
generate-id(key('contacts-by-surname', surname))]" mode="groups"/>
     </body>
   </html>
</xsl:template>
 
<xsl:template match="contact" mode="groups">
   <ul>
   <xsl:value-of select="surname"/>,<br/><xsl:apply-templates
select="key('contacts-by-surname', surname)"/>
   </ul>
</xsl:template>
 
<xsl:template match="contact">
 &#160;&#160;&#160;&#160;&#160;&#160;<xsl:value-of
select="forename"/>&#160;(<xsl:value-of select="title"/>)<br/>
</xsl:template>
 
</xsl:transform>
 
which does practically the same, it took only about 50 msec, 
which means a
performance gain of 750/50 = 15 times better!!
 
I haven't been able yet to test using the .NET XslTransform 
class, but that
will come in a later stage...
 
So for big input files and using MSXML 4.0, I would rather 
use the second
approach.... wouldn't you all agree? 
 
And if so, shouldn't the second method not be the first (and 
preferred)
method mentioned by Jeni (after all, everyone points to that 
page at first
instance)?
 
<prs/>
http://www.pietsieg.com <http://www.pietsieg.com/> 
http://www.pietsieg.com/dotnetnuke
Contributor on www.ASPToday.com <http://www.asptoday.com/> 
Co-author on "Professional ASP.NET XML with C#", July 2002 by 
Wrox Press

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