[Qgis-developer] Possible memory leak in rendering code

John C. Tull jctull at gmail.com
Mon Apr 22 19:25:29 PDT 2013

On Apr 22, 2013, at 2:12 PM, Nyall Dawson <nyall.dawson at gmail.com> wrote:

>> By the way, it would be a good thing to remove render caching
>> completely before 2.0. In any case it will need to be reworked when
>> moving to multi-threaded rendering... it has only a limited
>> functionality of storing previously rendered map in each layer and
>> reusing it in case the extent has not changed. Unfortunately the
>> rendered image is stored directly within QgsMapLayer class - in order
>> to work properly, the cache should be kept internally within each
>> QgsMapRenderer instance.
> -1 from me -- please don't do this! I realise that it has some
> limitations, but render caching makes a huge difference in speed with
> my workflow.
> I frequently use layers based off complex PostGIS views which take a
> long time to generate. With render caching I'm able to selectively
> toggle layers on/off or rearrange them for comparison without having
> to wait for QGIS to request a new version of the view from the PostGIS
> server. If I switch off render caching then every change to layer
> visibility or ordering triggers a refresh of the view and a painful
> wait in QGIS.
> Obviously an ideal solution would be to cache the PostGIS layer
> locally, but until that's possible render caching helps a lot...
> Nyall

Unfortunately, the render caching feature has never worked on OSX. It is a greyed out option in the settings because the code was never stable on this platform. If it is meant to be a program feature, it would ideally be one that is available on all platforms.


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