[QGIS-Developer] AFS feature iterator logic

[Alexis R.L.]

Greetings,

I'm looking into the web service data fetching and I noticed that there are
some things that seemed strange at first glance and wanted to know if
someone had insight into things.

>From what I understand data is fetched and cached and on the initial fetch
it seems that all the data is fetched? This may be to fill up the data
cache.

In the instances where an extent is present in the feature request, the
extent is used to perform check during the iteration, at each step it seems
that all the feature ids within the extent are requested, (see
https://github.com/qgis/QGIS/blob/693422bdc010713d4d15a1af6d0c04cc6a2e913d/src/providers/arcgisrest/qgsafsfeatureiterator.cpp#L131
) instead of being consolidated once with the requested Ids at the start?

In some cases during the test I am zoomed on two feature but there is a
request for an extent that return nearly 50 ids, I'm not sure what is
firing this as I didn't change the extent nor did any manipulation.

I'm not sure if things are similar for WFS but that stood out to me and I
don't understand too much why so much data may be requested, this is mostly
since I'm looking into ways to generate smaller index based only on the
extent of the canvas, as I think that it may be possible to avoid indexing
entire web layers if only a fraction of them are needed for snapping during
data manipulation.

Cheers,

Alex
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