[QGIS-Developer] Preview job and slow datasources

[Patrick Dunford]

Most of them are geoJpeg, there are a smaller number of geoTiff


On 17/11/17 20:10, Matthias Kuhn wrote:
>
> 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>
>>>>>>>
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>>>>>>>
>>>>>>
>>>>>>
>>>>>>
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