Re: [xsl] Performance of xsl:for-each with key() lookup

Subject: Re: [xsl] Performance of xsl:for-each with key() lookup
From: "Michael Kay mike@xxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
Date: Wed, 26 Sep 2018 22:07:46 -0000
Shame that the download link no longer works. And I'm not sure I've got an
archive version either, I think I was assuming at the time that putting things
on the web gave them permanence.

I do remember that the early attempts at streaming gave me no end of trouble,
and were soon abandoned. The analysis of what was streamable and what wasn't
was hopelessly fragile.

Michael Kay
Saxonica

> On 26 Sep 2018, at 22:50, Wendell Piez wapiez@xxxxxxxxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hey Alan, check out version 4, I'm sure Mike Kay doesn't remember the
> details of that one either --
>
> https://markmail.org/message/bapqkmmd7bz2fxce
>
> Probably wasn't providing late variable binding.
>
> Still giving great value! So far we have come!
>
> Cheers, Wendell
>
> On Wed, Sep 26, 2018 at 5:01 PM Alan Painter alan.painter@xxxxxxxxx
> <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>>
>> 10 years old and still giving great value.
>>
>> On Wed, Sep 26, 2018, 22:54 Michael Kay mike@xxxxxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>>>
>>> The answer obviously depends on the processor.
>>>
>>> With Saxon, if a variable is only referenced once, and the reference isn't
in a loop, then it will be inlined. So if you write
>>>
>>>>  <xsl:variable name="elems" select="key('some', $value, $doc)"
>>>> as="element()*"/>
>>>>   <xsl:for-each select="$elems">
>>>
>>> then Saxon will rewrite it as
>>>
>>>> <xsl:for-each select="key('some', $value, $doc)">
>>>
>>> The main benefit of this rewrite is better pipelining. A variable causes
the list of items to be stored somewhere in memory; without the variable, each
item is processed as soon as it is found.
>>>
>>> Michael Kay
>>> Saxonica
>>>
>>> PS: Saxon 9.1 is about 10 years ago, so my memory of it is rather rusty.
>>>
>>>
>>>> On 26 Sep 2018, at 21:40, Martynas JuseviD
ius martynas@xxxxxxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>>>>
>>>> Hi,
>>>>
>>>> I'm using the following pattern in multiple places in my stylesheets:
>>>>
>>>>   <xsl:for-each select="key('some', $value, $doc)">
>>>>
>>>> My question is, would iteration be optimized if I selected the nodes
>>>> into a variable first?
>>>>
>>>>   <xsl:variable name="elems" select="key('some', $value, $doc)"
>>>> as="element()*"/>
>>>>   <xsl:for-each select="$elems">
>>>>
>>>> I guess it should be faster if the key() function is called only once
>>>> instead of multiple times? But if there is an index maybe it doesn't
>>>> matter?
>>>>
>>>> And does the same apply to
>>>>
>>>>   <xsl:apply-templates select="key('some', $value, $doc)"/>
>>>>
>>>> as well?
>>>>
>>>> I'm using Saxon 9.1.0.8.
>>>>
>>>>
>>>> Martynas
>>>>
>>>
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>
>
> --
> Wendell Piez | http://www.wendellpiez.com
> XML | XSLT | electronic publishing
> Eat Your Vegetables
> _____oo_________o_o___ooooo____ooooooo_^

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