[QGIS-Developer] Preview job and slow datasources

[Matthias Kuhn]

Thanks, that's an interesting information.

What datatype are your rasters?


On 11/17/2017 03:53 AM, Patrick Dunford wrote:
>
> With the second command
>
> iface.mapCanvas().setPreviewJobsEnabled(False)
>
> when I run that command it drops back to 16 GB
>
>
> On 16/11/17 23:15, Matthias Kuhn wrote:
>>
>> Hi Patrick,
>>
>> Would be interesting to do this test with previews enabled and
>> disabled. Then we'll see if it's actually the previews or some other
>> mechanism that is causing this.
>>
>> IIRC only a composite image is saved in the preview jobs and not each
>> layer separately, but that's just what I remember and not evidence based.
>>
>> You can enable them in the python console with
>>
>>     iface.mapCanvas().setPreviewJobsEnabled(True)
>>
>> and disable with
>>
>>     iface.mapCanvas().setPreviewJobsEnabled(False)
>>
>> Thanks for a feedback
>>
>> Matthias
>>
>>
>> On 11/16/2017 08:42 AM, Patrick Dunford wrote:
>>>
>>> In my current project using Qgis 2.99, turning off the rasters uses
>>> 16 GB, turning them on uses 52 GB
>>>
>>> I do not believe it is independent from the number of layers that
>>> are being displayed.
>>>
>>> Previous versions of the software did not cache every single raster
>>> (the number of rasters actually being displayed on the canvas at any
>>> one time is a small fraction of the total number in the project)
>>>
>>> On 16/11/17 20:11, Matthias Kuhn wrote:
>>>>
>>>> Hi Patrick,
>>>>
>>>> This uses some memory (~ canvas width pixels * canvas height pixels
>>>> * 8 preview images * 32 bit RGBA), so let's assume 50 MB to 100 MB.
>>>>
>>>> This consumption is independent from the number or type of layers.
>>>>
>>>> Matthias
>>>>
>>>>
>>>> On 11/16/2017 08:02 AM, Patrick Dunford wrote:
>>>>>
>>>>> So to put it another way this is the reason why Qgis wants to use
>>>>> a huge amount of memory (40 GB) when I have a lot of raster images
>>>>> loaded in the background.
>>>>>
>>>>>
>>>>> On 16/11/17 18:56, Tim Sutton wrote:
>>>>>> Hi
>>>>>>
>>>>>>> On 16 Nov 2017, at 04:35, Patrick Dunford
>>>>>>> <enzedrailmaps at gmail.com <mailto:enzedrailmaps at gmail.com>> wrote:
>>>>>>>
>>>>>>> What is this "preview job" function?
>>>>>>>
>>>>>>>
>>>>>>
>>>>>> Its application logic to prefetch / pre-render offscreen content
>>>>>> in anticipation of user panning the map.
>>>>>>
>>>>>> Regards
>>>>>>
>>>>>> Tim
>>>>>>>
>>>>>>> _______________________________________________
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>>>>>> —
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> *Tim Sutton*
>>>>>>
>>>>>> *Co-founder:* Kartoza
>>>>>> *Project chair:* QGIS.org <http://QGIS.org>
>>>>>>
>>>>>> Visit http://kartoza.com <http://kartoza.com/> to find out about
>>>>>> open source:
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>>>>>>
>>>>>
>>>>>
>>>>>
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