[Qgis-developer] slow raster loading

[Tim Sutton]

Hi

On Wed, Aug 10, 2011 at 12:25 PM, Marco Hugentobler
<marco.hugentobler at sourcepole.ch> wrote:
>> 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.
>

Ya you make a good point. I will try update it to calculate on demand.

Regards

Tim

> 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
>



-- 
Tim Sutton - QGIS Project Steering Committee Member (Release  Manager)
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