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

[David Marteau]

Hi,

 > You should set the other new read optimisation flags here -- see 
https://github.com/qgis/QGIS/blob/88ebb3f2f513dbce5a775f50e51ea0117f859c65/src/core/qgis.h#L1962

These are already available also in 3.24 and we use the   
`TrustLayerMetadata` in the above test. For server,  the other flags are 
not applicable (Getprint requests need print layouts ).

So that mean we are comparing 3.24 to 3.26 with same level of read 
optimisation and that does not change the fact that, for that very same 
level of read optimisation, project's loading is incredibly  slower in 3.26.


Le 20/06/2022 à 15:10, Nyall Dawson a écrit :
>
>
> 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 <http://www.3liz.com>
>
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