[Qgis-developer] slowness reading shp

[Martin Dobias]

Hi Paolo

On Fri, Feb 18, 2011 at 4:47 PM, Paolo Cavallini <cavallini at faunalia.it> wrote:
> Hi all.
> I return on the old bug  https://trac.osgeo.org/qgis/ticket/1978
> I have done some testing, and in fact QGIS is almost unusable with large
> and complex data sets (see e.g.
> https://int.faunalia.it/~paolo/slow.tar.gz ). Adding caching helps, but
> this is proving to be a real stumbling block, preventing real world use
> in some cases. I checked, and unfortunately proprietary sw opens the
> same file much faster, and subsequent zooming and panning etc. is also
> much smoother. According to the trac, also other free sw is much faster.
> Can someone help me understand in which direction to work to solve this?

The main performance killer here is painting of borders. The layer is
rendered several times faster if you set border style to "no pen".
Also disable anti-aliasing - that also eats a lot of time. Build
spatial index to speed up rendering of small parts of the map.

The clear direction is to merge threading branch to trunk. It contains
some optimizations for rendering, plus it does not freeze while
rendering and continuously updates the map. So even when working with
huge layers, it's possible to see how rendering continues and zoom/pan
to desired region of interest without having to wait until rendering
of the last map finished.

Martin