> From: christian.gruen@gmail.com
> Date: Thu, 30 Jan 2014 21:54:06 +0100
> Subject: Re: [basex-talk] Use of attribute index
> To: r_schlichtner@hotmail.com
> CC: basex-talk@mailman.uni-konstanz.de
>
> Hi Robert,
>
> thanks for your precise observations. I agree that the second query
> should have been optimized as well, and is now rewritten in the latest
> snapshot [1] (the optimizer was bold enough to reject all path
> expressions that contained any positional predicates).
>
> Hope this helps,
> Christian
>
> [1] http://files.basex.org/releases/latest/
>
>
>
> On Thu, Jan 30, 2014 at 3:25 PM, Robert schlichtner
> <r_schlichtner@hotmail.com> wrote:
> > Hello,
> >
> > I found that a number of similar queries have quite different performance:
> >
> > xquery
> > doc('mcev_temp_5/20140130_11_55_40.xml')//column[@name='KLV_m1_rdr']/v takes
> > only 0.68ms, which is great.
> >
> > But xquery
> > doc('mcev_temp_5/20140130_11_55_40.xml')//column[@name='KLV_m1_rdr']/v[1]
> > takes 1479.81ms.
> >
> > If I change this to the equivalent (for my data) xquery
> > (doc('mcev_temp_5/20140130_11_55_40.xml')//column[@name='KLV_m1_rdr'])/v[1]
> > it runs fast again (0.53ms)
> >
> > Checking the query execution plan I found that only query 1 and 3 utilize
> > the attribute index.
> >
> > I find this rather surprising, and I would like to ask if there is some
> > general reason/rule why the second can not use the index, so I can avoid
> > such 'bad' queries in the future.
> >
> > Thanks!
> >
> > (I am using BaseX 7.7.2 on Windows XP.)
> >
> > Regards,
> >
> > Robert
> >
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