[Qgis-developer] Performance of QGIS expressions "attribute" and "get_feature"

[Stefan Ziegler]

Hi Nyall

I compared 2.12 with current master. But I don't see an improvement.
Opening the attribute table takes around 10 seconds for layers with approx.
2000 features with one virtual field (with the attribute(get_feature())
expression). Rendering is also really slow when using rule based renderer
on the virtual field.

regards
Stefan

On Wed, Dec 30, 2015 at 7:22 PM, Nyall Dawson <nyall.dawson at gmail.com>
wrote:

>
> On 31 Dec 2015 2:01 AM, "Stefan Ziegler" <stefan.ziegler.de at gmail.com>
> wrote:
> >
> > Hi
> >
> > I add a virtual field to a layer with e.g. following expression
> >
> > attribute(get_feature('pnf_pnf','t_id',afrom),'year')
> >
> > This works really great. Then I'm using this new virtual field for
> filtering the features in the rule based renderer. How does affect this the
> rendering performance? It seems that it really slows down rendering even
> with layers with only approx 600 features each.
> >
> > If so, can the speed improved with e.g. some to develop caching
> mechanism?
>
> Try with the current master version - this should be MUCH faster now. I'd
> love to hear any feedback of how you find the changes improve (or don't
> improve!) your situation.
>
> Nyall
>
> >
> > regards
> > Stefan
> >
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