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

Nyall Dawson nyall.dawson at gmail.com
Wed Dec 30 12:27:16 PST 2015


On 31 December 2015 at 06:18, Stefan Ziegler
<stefan.ziegler.de at gmail.com> wrote:
> 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.

What's the data source for each layer? If it's in a database (eg
postgres), is there a suitable index on the joined field?

Nyall



>
> 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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>


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