[QGIS-Developer] Qgis server: terrible performance with Qgis 3.26

[Nyall Dawson]

On Mon, 20 June 2022, 9:37 pm David Marteau via QGIS-Developer, <
qgis-developer at lists.osgeo.org> wrote:

> Hi,
>
> I have noticed a huge drop of performance while testing Qgis server with
> Qgis 3.26, from 10x to 30x slower as usual.
>
> Trying to reduce the problem I have found a huge increase of time spend
> reading the project in 3.26 compared to 3.24.
>
> Here some benchmark with very simple project from the test data set. Note:
> the project has been updated with qgis 3.26:
>
> Qgis 3.24:
> ======
>
> readflags = QgsProject.ReadFlags()
> readflags |= QgsProject.FlagTrustLayerMetadata
>
> prj = QgsProject()
>
> %timeit -n 1 prj.read(f"{datapath}/france_parts.qgs",readflags)
>
> > 15.7 ms ± 205 µs per loop (mean ± std. dev. of 7 runs, 1 loop each)
>
> Qgis 3.26:
> ======
>
> readflags = QgsProject.ReadFlags()readflags |= QgsProject.FlagTrustLayerMetadata
>
>
You should set the other new read optimisation flags here -- see
https://github.com/qgis/QGIS/blob/88ebb3f2f513dbce5a775f50e51ea0117f859c65/src/core/qgis.h#L1962

Nyall

​prj = QgsProject()
>
> %timeit -n 1 prj.read(f"{datapath}/france_parts.qgs",readflags)
>
> 195 ms ± 44 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
>
> There is a factor x10 between Qgis 3.24 et Qgis 3.26 for the exact same
> project.
> This has serious impact on requests: landing page catalog request time
> increased from approximatevely 110ms to more than 3.0s with our test data
> set.
>
> David Marteau
> www.3liz.com
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