Re: Merging 2 XML's in to 1 output XML (Performance I

> say for each record in InputXSL1 with Key match in InputXSL2 get 
                                       ^^^^

The answer is (probably) in your description. You are repeatedly
traversing the other tree to find a st:VehicleTT with the same DFFileId
as the current node. xsl:key is designed to optimise such access 9often
by orders of magnitute).

<xsl:template match="//st:VehicleTT">

You don't want the // there (all it does is change the priority, nit the
nodes matched)

I think you just want
<xsl:stylesheet version="1.0">

<xsl:output method="xml" indent="yes" />

<xsl:variable name="aggregator" select="document('InputXML2.xml')" />

<xsl:template match="/">
	<st:VehicleTDoc>
  		<xsl:apply-templates/>
	</st:VehicleTDoc>
</xsl:template>

<xsl:key name="v" match="st:VehicleTT" use="concat(xdd:DFFileId,':',xdd:RSNo)"/>

<xsl:template match="st:VehicleTT">
    <st:VehicleTT>
	    <xsl:copy-of select="*"/>
<xsl:variable name="key" select="concat(xdd:DFFileId,':',xdd:RSNo)"/>
<xsl:for-each select="$aggregator">
 <xsl:copy-of select="key('v',$key)/xdd:SName"/>
</xsl:for-each
</xsl:template>
	
</xsl:stylesheet>


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