[QGIS-Developer] Preview job and slow datasources

[kimaidou]

Hi,

I was wondering if these preview jobs are enabled in QGIS Server context,
when requesting a GetMap from any client. I am pretty sure the context of
the preview jobs execution is related to Desktop, but I would like to be
sure.
Any hint on this ?

Regards,
Michaël

2017-11-16 11:15 GMT+01:00 Matthias Kuhn <matthias at opengis.ch>:

> 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> 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
>
>
> _______________________________________________
> QGIS-Developer mailing list
> QGIS-Developer at lists.osgeo.org
> List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
>
>
> —
>
>
>
>
>
>
> *Tim Sutton*
>
> *Co-founder:* Kartoza
> *Project chair:* QGIS.org
>
> Visit http://kartoza.com to find out about open source:
>
> Desktop GIS programming services
> Geospatial web development
> GIS Training
> Consulting Services
>
> *Skype*: timlinux
> *IRC:* timlinux on #qgis at freenode.net
>
>
>
>
> _______________________________________________
> QGIS-Developer mailing listQGIS-Developer at lists.osgeo.org
> List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
>
>
>
>
> _______________________________________________
> QGIS-Developer mailing listQGIS-Developer at lists.osgeo.org
> List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
>
>
>
>
> _______________________________________________
> QGIS-Developer mailing listQGIS-Developer at lists.osgeo.org
> List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
>
>
>
> _______________________________________________
> QGIS-Developer mailing list
> QGIS-Developer at lists.osgeo.org
> List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-developer/attachments/20171116/07bfac2e/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: KartozaNewLogoThumbnail.jpg
Type: image/jpeg
Size: 6122 bytes
Desc: not available
URL: <http://lists.osgeo.org/pipermail/qgis-developer/attachments/20171116/07bfac2e/attachment-0001.jpg>