[Qgis-developer] slow raster loading

[Marco Hugentobler]

> I think the overhead for reading the aux.xml file is really minimal
> and the min/max population of that if its not there is quite quick and
> a once off event so I wouldnt think it is going to impact the server
> much. I'd suggest I first run some benchmarks to see how much overhead
> it adds.

But is there any downside from populating min/max on demand (e.g. like in 
QgsVectorDataProvider::minimumValue / maximum Value)? 

While it's nice to have a minimal overhead (probably buffered by the qgis 
server layer cache in many cases), it would be even better to have 0 overhead.

Regards,
Marco

> Am Mittwoch, 10. August 2011, 11.50:16 schrieb Tim Sutton:
> Hi
> 
> On Wed, Aug 10, 2011 at 8:31 AM, Marco Hugentobler
> 
> <marco.hugentobler at sourcepole.ch> wrote:
> > Btw, is it possible to call computeMinMax() on demand, e.g. in
> > QgsGDALProvider::minimumValue /maximumValue instead of the provider
> > constructor?
> > 
> > It probably does not matter much for the desktop experience. However, for
> > server throughput, avoidance of opening and parsing the aux.xml file
> > could make a difference.
> 
> I think the overhead for reading the aux.xml file is really minimal
> and the min/max population of that if its not there is quite quick and
> a once off event so I wouldnt think it is going to impact the server
> much. I'd suggest I first run some benchmarks to see how much overhead
> it adds.
> 
> Regards
> 
> Tim
> 
> > Regards,
> > Marco
> > 
> > Am Dienstag, 9. August 2011, 21.46:45 schrieb Tim Sutton:
> >> Hi Paolo
> >> 
> >> Does it do that every time you load that layer or only the first time?
> >> Does the filesystem permissions allow writing of gdal .aux.xml files?
> >> 
> >> My raster stats branch merge changed some behaviours and it is
> >> probably a side effect of that. One of the changes is that gdal gets
> >> full stats when trying to determine the min max of a band. It will
> >> fetch those stats quickly from aux.xml if present of if not its going
> >> to do a full stats gather just for the basic min max stats which is
> >> where you probably experience the slowness. I will see if I can find a
> >> better way to do the basic min/max stats gathering.
> >> 
> >> Regards
> >> 
> >> Tim
> >> 
> >> On Tue, Aug 9, 2011 at 3:49 PM, Paolo Cavallini <cavallini at faunalia.it>
> > 
> > wrote:
> >> > Hi all.
> >> > With current master, I get bad performances in loading rasters (a
> >> > <12Mb takes >5 sec); when double-clicking it from the QGIS browser,
> >> > it is far slower (>20 sec). From the console:
> >> > Warning: Object::connect: No such signal
> >> > QgsGdalProvider::statusChanged( QString ) in
> >> > /storage/build/Quantum-GIS/src/core/raster/qgsrasterlayer.cpp:2446 Any
> >> > hint?
> >> > All the best.
> >> > --
> >> > Paolo Cavallini: http://www.faunalia.it/pc
> >> > _______________________________________________
> >> > Qgis-developer mailing list
> >> > Qgis-developer at lists.osgeo.org
> >> > http://lists.osgeo.org/mailman/listinfo/qgis-developer
> > 
> > --
> > Dr. Marco Hugentobler
> > Sourcepole -  Linux & Open Source Solutions
> > Churerstrasse 22, CH-8808 Pfäffikon SZ, Switzerland
> > marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
> > Technical Advisor QGIS Project Steering Committee


-- 
Dr. Marco Hugentobler
Sourcepole -  Linux & Open Source Solutions
Churerstrasse 22, CH-8808 Pfäffikon SZ, Switzerland
marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee