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

[Even Rouault]

Use sysprof or just run under a debugger and interrupt regularly should 
help you spot in which method(s) most time is spent

Le 20/06/2022 à 18:48, David Marteau via QGIS-Developer a écrit :
>
> I used the following test:
>
> readflags = Qgis.ProjectReadFlags() readflags |= 
> Qgis.ProjectReadFlag.TrustLayerMetadata|Qgis.ProjectReadFlag.DontLoad3DViews|Qgis.ProjectReadFlag.DontLoadProjectStyles 
> prj = QgsProject()%timeit -n 1 
> prj.read(f"{datapath}/france_parts3_26.qgs",readflags)
>
> 105 ms ± 18.5 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
>
> This improve the result  but we are still much higher that the loading 
> time of 3.24: 15ms compared to 105ms
>
>
> Le 20/06/2022 à 18:38, Nyall Dawson a écrit :
>>
>>
>> On Mon, 20 June 2022, 11:42 pm David Marteau, <dmarteau at 3liz.com> wrote:
>>
>>     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.
>>
>>
>> You'll need to set the new flags relating to skipping the 3d views 
>> and project style loading in order to compare properly. Neither of 
>> those things were occurring in 3.24, and both have an associated 
>> cost. And neither are relevant for server.
>>
>> Nyall
>>
>>
>>
>>     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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>>>         QGIS-Developer at lists.osgeo.org
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>
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