[QGIS-Developer] Preview job and slow datasources

[Patrick Dunford]

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*
>>>
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>>
>>
>>
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