QGIS » QGIS Application

Each time the canvas is rendered, the rendering of GDAL raster layers is done with a new GDAL dataset object. Which means the dataset must be re-opened (potentially source of slowness), but more importantly, the GDAL block cache is of no use between 2 canvas rendering. For example when panning in the same area, cached tiles could potentially be reused. One can especially observe the slowness with slow compression methods (JPEG2000, LZMA, etc)

This issue didn't exist in ancient QGIS version (it exists in 2.8 and ongoing, perhaps older). This is due to the cloning of the QgsRasterPipe object at rendering.

Presumably some pool of GDAL dataset objects should be used to avoid those constant open & close operations