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Re: [xsl] Does <xsl:copy> use a lot of memory? Is there an alternative that is more efficient?

2012-09-02 10:35:06
In case the input document is parsed successfully, wouldn't the use of
<xsl:sequence> (instead of <xsl:copy-of>) result in using less memory?

Cheers,
Dimitre

On Sun, Sep 2, 2012 at 7:31 AM, Michael Kay <mike(_at_)saxonica(_dot_)com> 
wrote:
Memory is used for the source document and for intermediate variables. In
Saxon, and I suspect in most processors, no memory is used for the result
tree provided that the transformation is writing directly to a serializer.

Intrinsically, all xsl:copy has to do is to send two events - startElement
and endElement - to the serializer.

I would strongly suspect that the out of memory error occurs during building
of the source tree, and will happen whatever transformation  you run. For a
370Mb input document, you should probably allocate at least 2Gb of memory,
preferably more.

Michael Kay
Saxonica


On 02/09/2012 13:47, Costello, Roger L. wrote:

Hi Folks,

Does <xsl:copy> use a lot of memory?

Is there an alternative that is more efficient?

Consider this problem. I have an XML document in which some elements have
an id attribute and others have an idref attribute. If an element A
references element B, then I want to embed B inside A.

Example: I want to convert this:

<Test>
     <A idref="b" />
     <B id="b" />
</Test>

to this:

<Test>
     <A>
         <B id="b" />
     </A>
     <B id="b" />
</Test>

Notice that A references B, and after processing B is nested inside A.

Here's a template that handles elements with a reference:

     <xsl:key name="ids" match="*[@id]" use="@id"/>

     <xsl:template match="*[@idref]">
                  <xsl:variable name="refed-element" select="key('ids',
@idref)"/>
                  <xsl:copy>
             <xsl:copy-of select="@* except @idref" />
             <xsl:sequence select="$refed-element" />
         </xsl:copy>
              </xsl:template>

The complete program is below.

It works fine if:

(a) The XML document is small.
(b) I don't have to repeat this embedding process too many times.

However, such is not the case. I am dealing with an XML document that is
370 MB in size and has tens of thousands of references. And I have to repeat
the embedding process multiple times.

Saxon gives me an "out of memory error."

I suspect the reason for this is due to the <xsl:copy> command. I believe
it is making new copies, thereby consuming lots of memory. True?

So, is there an alternative to <xsl:copy> that is more efficient?

Is there a way to express the above template rule that is more efficient?

/Roger

-----------------------------------------------------------------------------------------
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
                 exclude-result-prefixes="#all"
                 version="2.0">

     <xsl:output method="xml" />
          <xsl:key name="ids" match="*[@id]" use="@id"/>
          <xsl:template match="*[@idref]">
                  <xsl:variable name="refed-element" select="key('ids',
@idref)"/>
                  <xsl:copy>
             <xsl:copy-of select="@* except @idref" />
             <xsl:sequence select="$refed-element" />
         </xsl:copy>
              </xsl:template>
               <xsl:template match="node()">
                  <xsl:copy>
             <xsl:copy-of select="@*"/>
             <xsl:apply-templates />
         </xsl:copy>
              </xsl:template>

</xsl:stylesheet>

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-- 
Cheers,
Dimitre Novatchev
---------------------------------------
Truly great madness cannot be achieved without significant intelligence.
---------------------------------------
To invent, you need a good imagination and a pile of junk
-------------------------------------
Never fight an inanimate object
-------------------------------------
To avoid situations in which you might make mistakes may be the
biggest mistake of all
------------------------------------
Quality means doing it right when no one is looking.
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Facts do not cease to exist because they are ignored.
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I finally figured out the only reason to be alive is to enjoy it.

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