[postgis-devel] estimating quality of spatial indexes

[Paul Ramsey]

Yes, I think the n-d index is still ang-tan.
Oleg and Teodor's site had some code for visualizing r-tree boxes that
could maybe be used to get a feel? Doing higher dimensions is going to
be difficut, I would imagine.
P.

On Mon, Mar 2, 2015 at 10:54 AM, Sandro Santilli <strk at keybit.net> wrote:
> I'm running performance tests with n-dimensional data and
> found cases in which fetching 5 points out of ~35 million
> can take 20K reads _or_ 2K reads depending on whether the
> Z/M selectivity is higher or the 2d selectivity is.
>
> In other words, if the query box is large but "low" it takes
> 10 times more seeking than if it is narrow but tall.
>
> I guess this has to do with the way splits were choosen and of
> course to the distribution of the data. To know more about the
> case I'd like to be able to "see" the index volumes in some way.
>
> Do you have ideas about how to visualize contents of the index ?
> I remember someone did it a long time ago.
>
> Another though is that the 2d index was changed 2 years ago
> to use Korotkov ( double-sorting ) approach for splitting, whereas the
> nd seems to be still using Ang-Tan one, is that correct ?
>
> REF: http://en.wikipedia.org/wiki/R-tree
>      http://trac.osgeo.org/postgis/ticket/1895
>
> --strk;