[QGIS-Developer] QGIS WMS provider firing too many requests !?

[pathmapper]

Hi,

here's a related thread (i.e. xyz tiles, but I guess it's also valid vor 
wms):
https://github.com/qgis/QGIS/issues/34813

Some quotes:
"QGIS renders the surrounding areas in a background job to make 
subsequent pan actions faster. Therefore it sends more tile requests 
than necessary for the current map extent."

"Btw, we now have the code in place to fine-tune prefetching behavior 
for all raster layers on a per-layer basis, for now I just blacklisted 
osm tiles."

It sounds like the plan is to make the prefetching behavior configurable 
via QGIS settings.

Cheers,
Bjoern

On 13.02.2021 19:45, Jeff McKenna wrote:
> Hi Richard,
> 
> Yes I've noticed this also, I just never spent time to examine why.
> For example, using my own WMS service I zoomed in and QGIS fired 11
> GetMap requests to my server.  It's difficult to trigger though (I
> can't reproduce with your NL service).  Bizarre.  But I have
> definitely seen 9+ GetMap requests for the same service/layer.
> 
> -jeff
> 
> 
> 
> 
> 
> 
> --
> Jeff McKenna
> GatewayGeo: MapServer Consulting and Training Services
> co-founder of FOSS4G
> http://gatewaygeo.com/
> 
> 
> 
> 
> 
> On 2021-02-13 11:29 a.m., Richard Duivenvoorde wrote:
>> Hi,
>> 
>> As a vivid WMS user/debugger, I see that QGIS is firing 9 requests per 
>> 'view-extent' currently.
>> 
>> I'm aware of cache etc etc... but... especially when using temporal 
>> filters for example, do others agree with me that this is more or less 
>> useless?
>> I'm also aware that a lot of WMS are actually just WMS interfaces in 
>> front of a cached WMTS, but still.
>> 
>> - some (governmental) services nowadays are still free for fair use, 
>> but: firing 9 times the actual requests costs resources/energy/maybe 
>> money
>> - before the WMTS I ran WMS services sometimes with pretty heavy 
>> styling, so on higher zoomlevels you do NOT want your clients to fire 
>> 9 requests, and just effectively use 1 ...
>> 
>> So in short: should I try to add some kind of (hidden?) option to 
>> minimize the number of requests?
>> 
>> To test a wms of all municipalities of NL:
>> 
>> https://geodata.nationaalgeoregister.nl/bestuurlijkegrenzen/ows?SERVICE=WMS
>> (layer 'gemeenten', EPSG:28992)
>> And look in F12/debugging window the number of GetMap requests fired 
>> when zoomed in...
>> 
>> I copied/created polgyons of the requests, and (see screenie) indeed 
>> looking at the center 'tile', the 8 surrounding requests are also 
>> fired....
>> 
>> Currently looking into this.
>> 
>> Regards,
>> 
>> Richard Duivenvoorde
>> 
>> 
>> 
> 
> 
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