Hi Patrick , did you consider using GDAL VRT to avoid opening so much files? In my experience, this works well. Régis
2017-10-05 13:48 GMT+02:00 Patrick Dunford <blackwhite...@gmail.com>: > Some time ago in a discussion of a particular bug a contributor expressed > concern that the refresh of background rasters (aerial photography) in > Windows was too slow. > > Maybe this is the reason that recent versions of master appear to be > loading all of the background imagery into memory (I use a master from > January this year to work around issues with later ones, and that master > does not have this feature). > > Unfortunately if there are a lot of rasters then the memory demand is > excessive and unsurprisingly slows down the computer negating any purported > benefit of caching. > > As an example a project I am currently working on has about 900 aerial > photo images (GeoJpeg). When the layer is turned on for display, Qgis > requires about 46 GB of virtual memory. Since my computer only has 24 GB of > physical memory, it is required to dip into the swap space considerably. > Even with 60 GB of swap space on an SSD, the swapping needed to refresh the > canvas is substantial and dramatically reduces performance resulting in > substantial delays. Compare with the January master referred to above which > only requires about 7 GB of virtual memory total with the aerial photo > layer displayed. The time needed to refresh the canvas is less than 1 > second, most of the time. > > I know that the canvas refresh in Windows with aerial photos can be > substantially slower than in Linux. This does not affect me, because I > don't use Windows now that I have a stable platform for running an older > Linux master alongside the most recent one. What I do know is that the > memory demands are making it difficult to evaluate the recent masters. I > need some kind of setting to turn this caching off. With the aerial photo > layer turned off, the memory usage of the current master is about the same > as the old one, and it's much quicker to update. > > > _______________________________________________ > QGIS-Developer mailing list > QGIS-Developer@lists.osgeo.org > List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
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