To complete the picture, I followed MK's advice and went to XMark - An
XML Benchmark Project, http://www.xml-benchmark.org/downloads.html,
and downloaded the ready-made-document of a 100 MB to see xsl:key at
work on a more realistic dataset.

To make transformations from inside Oxygen it was necessary to set
-Xmx256m up to -Xmx700m in oxygen.bat.

I used the following stylesheet:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="2.0">
    <!-- List the names of persons and the number of items they bought.
            (joins person, closed_auction) -->
    <xsl:output indent="yes"/>

       <xsl:template match="/">
           <items>
        <xsl:for-each select="/site/people/person">
            <xsl:variable name="a"
                select="/site/closed_auctions/closed_auction[buyer/@person =
                current()/@id]"/>
            <item person="{name}"><xsl:value-of select="count($a)"/></item>
        </xsl:for-each>
           </items>
       </xsl:template>
</xsl:stylesheet>

Saxon Home Edtion: 1. test: 876.9s, 2.test: 911.1s
Enterprise Edition: 1. test: 13.2s, 2. test: 13.0s both using
Optimization level 10.
Enterprise Edition: 3. test: 549.5s, 4. test: 556.5s using
Optimization level 1 and 5!

In Saxon's documentation we can read: "currently all values other than
0 results in full optimization but this is likely to change in
future." I don't understand why optimization level 1 and 5 are not as
good as 10 considering the documentation,  and I don't understand why
someone would want less than full optimization?

I then used the stylesheet below using xsl:key:

Saxon Home Edition: 1. test: 12.8s, 2. test: 13.1
That is: xsl:key in Home Edition is as good as the build in
optimization level 10 in Enterprise Edition making xsl:key not
necessary in EE in most situations.

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="2.0">
    <!-- List the names of persons and the number of items they bought.
            (joins person, closed_auction) -->
    <xsl:output indent="yes"/>
    <xsl:key name="k" match="/site/closed_auctions/closed_auction"
use="buyer/@person"/>

       <xsl:template match="/">
           <items>
        <xsl:for-each select="/site/people/person">
            <xsl:variable name="a"
                select="key('k', @id)"/>
            <item person="{name}"><xsl:value-of select="count($a)"/></item>
        </xsl:for-each>
           </items>
       </xsl:template>
</xsl:stylesheet>

Cheers,
Jesper Tverskov
http://www.xmlplease.com

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