On Sat, 2012-10-27 at 11:16 +0200, Sandro Santilli wrote: > On Sat, Oct 27, 2012 at 01:41:49AM +0200, Tim Sutton wrote: > > > * One of the major limitations I and the many people that contact me > > about QGIS experience is lack of performance. Just yesterday I got an > > email from someone in Sudan trying to use QGIS to work with ~300 000 > > point records and it taking 4 hours to do some simple operations on > > the dataset. > > I think such cases should be handled by only fetching a sample of the > data for visualization purpose, rather than the full set. And similarly > only a subset of vertices could be fetched when facing dense vectors. > > This is something that might need an API change too, as you would need > the providers to be told when the data has to be fetched only for > visualization (thus generalization is possible) or for editing (thus > you want all the data, possibly forcing a restriction on extent). > > Just my 2 cents. > > --strk;
Sounds like something worth considering. Something else I have been thinking of and what would increase performance pretty good in some situations would be to be able to select by an expression: myFeatureSet = provider.select( QgsExpression( 'attr1 = 1 AND attr2 > 5' ) ) while myFeatureSet.nextFeature(myFeature): do interesting stuff... I'm working here on a dataset with several thousand lines and I want create a rubberband on some of them (Lets say 500). Possibilities now are: * Request each single feature by id (It's based on a pg view which takes 0.5 seconds to be built, multiplied by 500: 250seconds...) * Request all features, iterate and check if it's in the list. This can also consume a considerable amount of time depending on the total cound of features. I guess what I'm talking about could be called Database Abstraction Layer. -- Matthias (Sorry for the thread hijacking) > > http://www.cartodb.com - Map, analyze and build applications with your data > > ~~ http://strk.keybit.net > > _______________________________________________ > Qgis-developer mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/qgis-developer _______________________________________________ Qgis-developer mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/qgis-developer
