[Qgis-developer] Simplify provider side

[Médéric Ribreux]

Hello,

I have made tests with SDO_UTIL.RECTIFY_GEOMETRY. I have used the 
following queries:

* SDO_UTIL.SIMPLIFY: SELECT SDO_UTIL.SIMPLIFY("GEOM", 1, 0.05) FROM 
"TABLE" WHERE ROWNUM < 10000
* SDO_UTIL.RECTIFY: SELECT SDO_UTIL.RECTIFY("GEOM", 0.05) FROM "TABLE" 
WHERE ROWNUM < 10000
* Direct geometry: SELECT "GEOM" FROM "TABLE" WHERE ROWNUM < 10000

And this is what I've found so far for performances:
* SDO_UTIL.SIMPLIFY: 12.3 seconds and 3.47 MBytes of traffic.
* SDO_UTIL.RECTIFY: 8.5 seconds and 3.37 MBytes of traffic.
* Direct geometry: 6.37 seconds and 5.09 MBytes of traffic.

It seems that SDO_UTIL.RECTIFY will also be a problem for provider 
simplification performances with Oracle.
Furthermore, in a vast majority, this function doesn't really simplify 
the geometry (same number of vertices produced).
"TABLE" has spatial indexes enabled and no geometry validation problem.

Perhaps there is nothing directly available in Oracle Database Spatial 
to handle simplification with a benefit on the final rendering speed in 
QGIS.
But, SDO_UTIL.SIMPLIFY actually do simplification on the provider side 
so why not implement it ?

The workaround could be a (conditional) warning somewhere on the dialog 
box for layer rendering (in Settings and in individual layer rendering 
tab) stating that Oracle simplification on the provider side is likely 
to degrade rendering performances...

Cheers !

Le 2016-02-02 11:33, A Huarte a écrit :
> The issue 12298 (https://hub.qgis.org/issues/12298) of Michael Douchin
> proposes the SDO_UTIL.RECTIFY_GEOMETRY function to simplify
> (https://hub.qgis.org/attachments/8488/QGIS_oracle_pre_rendering_simplification.diff).
> 
> I am sorry, but I don't have an Oracle database to test performance.
> Might someone test it before to create a new pull?
> Alvaro
> 
> -------------------------
>  DE: Paolo Cavallini <cavallini at faunalia.it>
> PARA: A Huarte <ahuarte47 at yahoo.es>; Médéric Ribreux
> <mederic.ribreux at medspx.fr>; kimaidou <kimaidou at gmail.com>
> CC: "qgis-developer at lists.osgeo.org" <qgis-developer at lists.osgeo.org>
> ENVIADO: Martes 2 de febrero de 2016 11:01
> ASUNTO: Re: [Qgis-developer] Simplify provider side
> 
> Il 02/02/2016 00:38, A Huarte ha scritto:
>> Finally the code was reverted. Thanks a lot to all for your tests!
> 
> too bad - no hope to have a proper fix?
> 
> thanks.
> 
> --
> Paolo Cavallini - www.faunalia.eu
> QGIS & PostGIS courses: http://www.faunalia.eu/training.html

-- 
Médéric RIBREUX
https://medspx.fr