Optimization and performance depend on the processor.

As it happens, with Saxon, if you use "//x" inside a loop then Saxon will
remember the value and avoid re-evaluating it each time, while if you use
/*/x, it won't.

The moral is, don't guess - measure!

Putting the value in a variable that's set outside the loop, whatever the
expression used, is almost certainly not going to make performance any
worse.

I don't think there's likely to be any significant difference between using
a single-valued key, as shown here, and using a global variable. Using a
global variable seems much more intuitive.

But here I'm guessing.

Michael Kay
http://www.saxonica.com/
 

> -----Original Message-----
> From: Geert Josten [mailto:Geert.Josten@xxxxxxxxxxx] 
> Sent: 03 November 2004 08:57
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject: Re:  A question on optimization
> 
> Hi Jochen,
> 
> >   <xsl:for-each select="//justus:choice">
> >     <xsl:element name="TR">
> >       <xsl:variable name="current" select="."/>
> >       <xsl:for-each select="//justus:part[@visible='true']">
> >         <xsl:variable name="dbfeld" select="."/>
> >         <xsl:element name="td">
> >           <xsl:for-each
> >              select="$current/@*[name()=$dbfeld/@dbfeld]">
> >             <xsl:value-of select="."/>
> >           </xsl:for-each>
> >         </xsl:element>
> >       </xsl:for-each>
> >     </xsl:element>
> >   </xsl:for-each>
> 
> ...
> 
> >    <xsl:for-each select="//justus:choice">
> >      <xsl:element name="tr">
> >        <xsl:element name="td"><xsl:value-of 
> select="a1"/></xsl:element>
> >        <xsl:element name="td"><xsl:value-of 
> select="a2"/></xsl:element>
> >        ...
> >      </xsl:element>
> >    </xsl:for-each>
> 
> David is right. Using // is rather expensive in terms of 
> performance. Use full paths as David 
> suggests, or try using keys if the choice and part elements 
> may occur in unpredictable locations:
> 
> <xsl:key name="choices" match="justus:choice" use="'all'" />
> <xsl:key name="parts" match="justus:part" use="'all'" />
> 
> <xsl:for-each select="key('choices', 'all')">
> 
> and
> 
> <xsl:for-each select="key('parts', 'all')[@visible='true']">
> 
> Grtz,
> Geert