Further investigation and comment
Since recently installing Qgis 3.4.15 or 3.4.14 on some of my computers
running Debian 10, I immediately began to see a trend of the software
exhibiting an increased tendency to crash when working with certain WMTS
layers that I had previously worked with extensively over recent weeks
for mapping purposes.
After attempting numerous changes including special versions of projects
containing no file based raster layers and only containing one WMTS
layer at a time and being unable to use the software regardless I
created a virtual machine running Debian 9 which has the latest version
available for that platform, 3.4.4. This has resulted in immediate major
improvement in the reliability of the software to the point I can resume
using it without the numerous crashes of the software that have been
noted recently, especially in the last week approximately.
On 27/01/20 1:19 am, 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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