Re: [Exist-open] Looking for best practice / advice on simple Xquery optimisation

[Patrick B. <pat...@jo...>]

This would be a great thing to test and provide back to the community.
While, I would guess that the first query would be faster, it would be
awesome to have actual benchmarks to refer to.

I've really wanted to start a community database of performance data and
optimization information for a while...

On Thu, Dec 1, 2011 at 8:07 AM, Joe Wicentowski <jo...@gm...> wrote:

> Hi Stéphane,
>
> > First of all I apologize if this is a naive question because just a
> matter of style.
>
> No, good question!
>
> > doc('/db/mycol/1.xml')/Data
> > vs.
> > collection('/db/mycol')/Data[@id = '1']
> >
> > Does it make any difference, is there a best way to write this query ?
>
> The queries are effectively identical, and I doubt you would notice a
> difference in performance.  But the first query likely has a slight
> performance edge over the second one.  The first query will be
> resolved solely based on eXist's structural index, whereas the second
> query requires that eXist read the contents of the @id attribute.  By
> default, reading the content of a node means leaving the indexes and
> accessing the DOM - which can be a slow operation.  But you can speed
> up the performance of such filters by defining a range index on @id.
>
> Some good reading on this topic can be found at
> http://exist-db.org/indexing.html and http://exist-db.org/tuning.html
> (and with in that article, see esp.
> http://exist-db.org/tuning.html#d1973e497).
>
> Cheers,
> Joe
>
>
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