[QGIS-Developer] Feature count for DB provider.

[Rémi Desgrange]

Hi,

Just launched the new QGIS 3.24, and tests the SQL debugger, I just found out that the “feature count” does a while loop on all features in the layer to count.

While it’s probably necessary for shapefiles or stuff like that, it appears suboptimal for databases access. I found this part in the code that looks like to be responsible for the feature counts, https://github.com/qgis/QGIS/blob/master/src/core/vector/qgsvectorlayerfeaturecounter.cpp#L76-L90

Do you think I could make a special case for database-based provider (geopackage, postgres/oracle/mysql/etc…) that launch a “SELECT count(*) FROM table” instead of looping on all features.

Thanks.
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