Hi Patrick -
Swap space is an internal component the underlying operating system (OS)
uses for handling memory request that exceeds the ram resources of the
computer. A normal user program like QGIS has no "knowledge" about this
facility and can't directly manipulate the swap system.
As Jonathan describes, "swap" space for for other program is temporary
file storage, usually placed in a specific directory (in windows
designated by the environment variable %TEMP%). QGIS uses this directory
too.
A QGIS crash can be caused by running out of memory resources and/or
temp file storage. However, that is result of a bad setup of your
operating system, which can limit how much swap space, that can be
allocated to memory hungry programs and the size of hard-disk used for
swap space and/or temp storage
So what to do:
1. Check memory consumption when using QGIS. Is it really using all the
ram - memory and starting to swap ?
2. Check the setup of the swap space parameters. It it using a
hard-disk which is running out of storage space.
3. Check the setup of the temp storage parameters. It it using a
hard-disk which is running out of storage space ? Are the user
allowed to allocate enough storage?
(I can't be more specific not knowing the operating system you use)
If the above checks out OK and you still have issues with QGIS crashing..
The shift from QGIS 2.x to QGIS 3.x meant a complete change of the
underlying graphics subsystem QT from ver 4.x to ver. 5.x (and a huge
amount of other changes).
One or more of those changes might cause a failure as you described.
However, you have to check the above and then write an error issue
(https://github.com/qgis/QGIS/issues) where you describe error messages,
your specific setup like operating system and version, QGIS version and
- if possible - test-data and project to replicate the issue.
--
Med venlig hilsen / Kind regards
Bo Victor Thomsen
Den 26-01-2020 kl. 13:19 skrev Patrick Dunford:
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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