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RE: [xsl] Does use a lot of memory? Is there an alternative that is more efficient?


Subject: RE: [xsl] Does <xsl:copy> use a lot of memory? Is there an alternative that is more efficient?
From: "Costello, Roger L." <costello@xxxxxxxxx>
Date: Mon, 3 Sep 2012 15:12:40 +0000

>> In other words, if I don't immediately output the results of
>> xsl:copy, then memory consumption grows and grows. Yes?
>
>Potentially yes.

Okay, then I am in a pickle and I see no way out.

Recall the problem that I am tackling: I have an element with an idref
attribute. I want to fetch the referenced element and inline it. Here's the
template to do that:

    <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>

However, the element that I just inlined may have a reference. So I store the
results into a variable and then repeat the process on the content of the
variable. But that may also result in inlining an element with a reference, so
I store the results into another variable and process it. I keep repeating
this process until there are no more references. (The references may be
recursive so it is a bit more involved than this, but you get the idea.)

I am processing a 370 MB XML document. The Java version of Saxon gives an "out
of memory" error. I increased the memory size to the maximum that my machine
would allow, 4 GB and I still get the "out of memory" error.

In the process I described above, I am creating a bunch of variables. But with
each new variable that I create, the previous variables are no longer used. It
seems like the previous variables should be garbage collected. Is there a way
to signal to an XSLT processor, "Hey, I am done with this variable, please
garbage collect it"?

/Roger



-----Original Message-----
From: David Carlisle [mailto:davidc@xxxxxxxxx]
Sent: Monday, September 03, 2012 10:06 AM
To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
Cc: Costello, Roger L.
Subject: Re: [xsl] Does <xsl:copy> use a lot of memory? Is there an
alternative that is more efficient?

On 03/09/2012 15:57, Costello, Roger L. wrote:
> In other words, if I don't immediately output the results of
> xsl:copy, then memory consumption grows and grows. Yes?

Potentially yes. But not really because of the xsl:copy, if you changed
it to xsl:sequence you'd probably get the same behaviour. If you are
using lots of variables and don't want them to take up space, you need
to have a very good idea how your xslt processor's optimiser works and
constrain your usage to uses which the optimiser can optimise away....

David


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