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AW: [xsl] extrem performance break down


Subject: AW: [xsl] extrem performance break down
From: "Szabo, Patrick (LNG-VIE)" <patrick.szabo@xxxxxxxxxxxxx>
Date: Wed, 12 Dec 2012 13:55:12 +0000

Thanks a lot for your detailed answer.
I don't think I undersand your approach.
Why does it make a difference if i search the pattern first and put it in a
vriable.  In  the end saxon will still have to search right ?



. . . . . . . . . . . . . . . . . . . . . . . . . .
Ing. Patrick Szabo
Developer
LexisNexis
A-1030 Wien, Marxergasse 25

mailto:Patrick.Szabo@xxxxxxxxxxxxx
Tel.: +43 1 53452 1573
Fax.: +43 1 534 52 146

. . . . . . . . . . . . . . . . . . . . . . . . . .

-----Urspr|ngliche Nachricht-----
Von: Michael Kay [mailto:mike@xxxxxxxxxxxx]
Gesendet: Mittwoch, 12. Dezember 2012 11:17
An: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
Betreff: Re: [xsl] extrem performance break down

I would have expected the first pattern to perform pretty badly, because of
the use of [following::text()], which means that every time you look at a
paragraph you also have to look at all the following text nodes.

But in your new pattern you are looking at all the preceding nodes of all the
ancestors, and you are doing this for every element, not only for selected
elements like p and ul.

You could probably get some improvement by reordering the predicates (the
optimum order is some combination of putting the cheapest-to-evaluate
predicate first, and putting the most-selective predicate first).

However, I would suggest a completely different approach. Whenever you have
match patterns that need to search the document like this, it's often best to
invert things: start by finding the nodes that match this complex condition
and put this node-set in a global variable $special, then replace your pattern
with

match="*[. intersect $special]"

Another point to be aware of with pattern matching in Saxon is that it will
always work best if Saxon can determine that the pattern will only match
elements of one particular element name. So you might well be better off
breaking this into separate patterns that start

p[....]
ul[....]
span[.....]

Michael Kay
Saxonica

On 12/12/2012 08:14, Szabo, Patrick (LNG-VIE) wrote:
> Hi,
>
> I'm using Saxon-B 9.0.0.6 that comes with Oxygen 9 for profiling.
> My Stylesheet is quite long so i don't wan't to post the whole thing but my
problems seems to reside within one template anyway.
>
> I have the following template:
>
> <xsl:template match="*[self::p or
self::ul][following::text()[starts-with(.,'Zum aktuellen Rechtsstand')] and
ancestor::div[@class='comm.body'] and text()][1]" priority="20">
>          ***something happens***
> </xsl:template>
>
> When i change the xpath to
>
> <xsl:template match="*[not(ancestor-or-self::span[@class='heading' and
count(preceding::span[@class='heading']) = 0])][self::p or self::ul or
self::span[not(@class='heading' and count(preceding::span[@class='heading']) =
0)]][following::text()[starts-with(.,'Zum aktuellen Rechtsstand')] and
ancestor::div[@class='comm.body'] and .//text()][1]" priority="20">
>          **still same things happens** </xsl:template>
>
> it adds 104 seconds to the execution time. Problem is i need to change it
because otherwise it matches thing it's not supposed to.
>
> Can anyone tell me what exactly I'm doing that is causing this performance
break ?
> As soo as i revert that one change execution time goes down again.
>
> cheers
>
>
> . . . . . . . . . . . . . . . . . . . . . . . . . .
> Ing. Patrick Szabo
> Developer
> LexisNexis
> A-1030 Wien, Marxergasse 25
>
> mailto:Patrick.Szabo@xxxxxxxxxxxxx
> Tel.: +43 1 53452 1573
> Fax.: +43 1 534 52 146
>
> . . . . . . . . . . . . . . . . . . . . . . . . . .


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