Re: [xsl] Speeding up processing (with sablotron or saxon)

Subject: Re: [xsl] Speeding up processing (with sablotron or saxon)
From: Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>
Date: Mon, 12 Jul 2004 19:03:57 -0400

At 01:33 PM 7/12/2004, you wrote:
ok I have a piece of XSLT that processes a large XML file into smaller
chunks. The problem I have is that the deeper down into the XML file I am
processing the longer it takes. Is this just due to the way XSLT parsers
work or can I tweak my XSL file so it processes faster?

I get the same effect when I used to process the file as one pass using
Saxon Result:document as I do processing as seperate XSL files with either
Saxon or Sablotron.

This is the seperate file XSL file:- (Change the server[@name='Ahazi'] as needed) <?xml version="1.0"?> <xsl:transform xmlns:xsl=""; version="1.0"> <xsl:output method="xml" indent='yes' encoding="utf-8"/>

<xsl:template match="server" />
<xsl:template match="server[@name='Ahazi']">

... this for-each is expensive. You are traversing the entire document looking for 'resource' elements; each one you find is examined by looking at all its preceding elements and comparing their @swgcraft_id attributes. When you have lots of elements, lots and lots of them are compared. (n^2 performance.)

Since this happens every time the template is matched (which could itself be lots of times), it adds up -- especially for the later nodes in your set (as you noticed).

An easy tweak to improve performance would be to use keys to de-duplicate instead of doing it by hand on the preceding:: axis.


<xsl:key name="resource-by-id" match="resource" use="@swgcraft_id"/>

<xsl:variable name="resources" select="//resource"/>
(binding //resource to a variable $resource so we don't have to retrieve it every single time)

then you can deduplicate in another variable declaration:

<xsl:variable name="unique-resources"
select="$resources[not(count(.|key('resources-by-id',@swgcraft_id)[1]) = 1)]"/>

In English: $unique-resources is the collection of all resources which, when counted along with the first resource with the same swqcraft_id as themselves, amount to a single node (which is true only of the first one with each swgcraft_id).

This ought to help quite a bit.


====================================================================== Wendell Piez mailto:wapiez@xxxxxxxxxxxxxxxx Mulberry Technologies, Inc. 17 West Jefferson Street Direct Phone: 301/315-9635 Suite 207 Phone: 301/315-9631 Rockville, MD 20850 Fax: 301/315-8285 ---------------------------------------------------------------------- Mulberry Technologies: A Consultancy Specializing in SGML and XML ======================================================================

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