Re: [xml-dev] Schematron tip: Use only one pattern

["Imsieke, Gerrit, le-tex" <gerrit.imsieke@le-tex.de>]

One reason for the acceleration could be that only the first matching 
rule within a pattern will be applied/evaluated. Roger, you might want 
to check whether the number of failed-asserts and successful-reports in 
the resulting SVRLs is the same for each scenario. It probably isn’t.

So putting all rules into a single pattern is not equivalent to having 
distinct patterns for each rule.

Gerrit


On 22/12/2017 14:59, Michael Kay wrote:
> > /“Why is validation so slow?”/I wondered.
> >
> > I did some digging and discovered the reason for the slowness. Recall 
> > that a Schematron schema is converted to an XSLT program. I looked at 
> > the XSLT program that was generated for my Schematron schema. Here’s 
> > what I found:
> >
> > <xsl:templatematch="/">
> > <xsl:apply-templatesselect="/"mode="M0"/>
> > <xsl:apply-templatesselect="/"mode="M1"/>
> > <xsl:apply-templatesselect="/"mode="M2"/>
> > <xsl:apply-templatesselect="/"mode="M3"/>
> >
> >       …
> > <xsl:apply-templatesselect="/"mode="M29"/>
> > </xsl:template>
> >
> > That says: Start at the top of the XML document and process the entire 
> > XML document, applying the template rules with mode M0. Then, start 
> > all over at the top of the XML document and process the entire XML 
> > document, applying the template rules with mode M1. And so forth.
> >
> > So, the entire 180 MB XML file gets processed 30 times.
> >
> > Eek!
> >
> > It’s no wonder that validation was so slow.
> It's interesting that this should make a big difference, but it's not at 
> all inevitable. I would expect that the actual navigation (selecting 
> child nodes) is very fast compared with the cost of evaluating match 
> patterns and executing the template rules, and since each pass of the 
> document is in a different mode, there should be very little cost for 
> processing nodes that are effectively skipped. So the reasons for the 
> slowness must lie a little deeper than you imagine. A lot will depend on 
> the actual match patterns present in each mode. And of course, on the 
> XSLT processor, since processors are likely to use very different 
> algorithms for trimming the search space for pattern matches.
>
> And going into meta mode, as one does on xml-dev: It's quite common for 
> a community to develop folk wisdom along the lines "don't do X, it's 
> very slow" based on an experience like this that might (or might not!) 
> turn out to have general applicability.
>
> With performance, the devil is always in the detail.
>
> Happy Christmas!
>
> Michael Kay
> Saxonica
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