[QGIS-Developer] QGIS virtual layer incredibly slow

[Andreas Neumann]

Hi Matteo and Toto,

Seems like I am not the only one that suffers from this slowness.

The same query that takes about 40 secs in a virtual layer runs in 200ms 
in Postgis. Now I know that there is a lot of overhead to bring the two 
different data sources (Postgis and Geopackage) together, but it still 
doesn't explain the 40 secs.

Also, the 40 secs would be ok, if it could be cached somehow throughout 
the QGIS session.

So if there would be some potential to introduce a caching mechanism to 
QGIS virtual layers, it would be much appreciated. There could be 
several update strategies: on opening of the project, on manual update 
(right-click layer --> update) or time based (e.g. every 5 minutes), or 
event based (if one of the involved layers changes).

Thanks,

Andreas

Am 02.05.19 um 11:23 schrieb matteo:
> Hi Andreas,
>
> I also noticed the slow rendering of virtual layers, also when a layer
> is small.
>
> I think it depends on the result of the query: with 50 points when
> linking one point with a line to all the other 49 points, at every map
> zoom in/out it takes seconds to refresh the query
>
> Cheers
>
> Matteo
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