[QGIS-Developer] [Qgis-user] Qgis crashes while loading WMTS layers

[Jonathan Moules]

Hi Patrick,
I can't comment on the core issue, but just a point for clarification - 
I thought Swap memory usage was something the operating system dealt 
with? Isn't it usually transparent to the application?

A quick search indicates that what GIMP calls swap is really a bespoke 
folder for GIMP to store temporary files (in a fashion similar to 
virtual memory/swap) rather than the system swap file; FME does this too 
(they call it a "temporary directory").

I can certainly see why that would have value - it looks like QGIS has 
one, at least for temporary outputs - 
https://github.com/qgis/QGIS/issues/28222 - but whether it's as well 
used as it should be I leave for others to comment on (I have no idea 
what it's used for).

Cheers,
Jonathan

On 2020-01-26 12:19, Patrick Dunford wrote:
> Good day to all.
>
> Not so long ago I wrote a post about issues handling large numbers of 
> raster files. This results from what appears to be an architectural 
> design limitation of Qgis in that it only has enough resources 
> available for a certain (unknown) number of raster layers and does not 
> have any effective system for dealing with the exhaustion of these 
> resources.
>
> I also noted that the software does not appear to have the ability to 
> use the swap (virtual memory) resources within a system to deal with 
> the apparent exhaustion of resources, as other software would. For 
> example, Gimp which I use for graphical editing is able to handle 
> certain projects using a swap space of 200 GB, which consists of 32 GB 
> of physical RAM and the rest in SSD. It is not unusual with some of 
> these graphics projects to have 100 GB or more of swap space in use, 
> without crashing the system. (This being possible since Gimp 2.10 with 
> its ability to write files of more than 4 GB)
>
> Whilst it is possible to manage the number of layers with file based 
> rasters, this cannot be done with a WMTS server because there is no 
> way I am aware of to manage the number of layers that can be 
> downloaded from the server.
>
> Version 2.18 and earlier almost never crashed with excess layers, 
> usually all that would happen is a layer would be displayed with 
> invalid data. However, crashes have become the norm with 3.x versions 
> of software.
>
> It seems to me there is a big architectural problem in the software 
> with its inability to utilise the full resources of the system in 
> order to process the number of layers that a WMTS server is capable of 
> issuing.
>
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