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Rendering a large MSSQL-Layer in QGIS 2.18 is very slow. The same segment takes in 2.14.1 about 10 seconds and in 2.18.3 about 2 minutes. In 2.16.1 or 2.18.1 it is also very slow.

What can be the reason for this?

EDIT:

My MSSQL-Layer has about 3,1 millions polygon-objects. I found out that the rendering-process is different in the two QGIS-Versions (2.14 and 2.18):

  • The drawing of the objects in full extent in QGIS 2.14 is scattered (not grouped together!). The objects come into sight scattered over the full extent of the map. Here is an image from the first seconds of rendering:

rendering in QGIS 2.14

If I scale then to a detail section, rendering is very fast.

  • Otherwise the drawing of the objects in full extent in QGIS 2.18 is grouped. The objects come into sight grouped in regions. Here is an image from the first seconds of rendering:

rendering in QGIS2.18

If I scale then to a detail section, rendering is very slow.

Is there a way to render the layer in 2.18 like in 2.14? Why is there a difference in the render process?

Was there a known general change in the render process in QGIS or could it be a wrong adjustment of my QGIS Installation?

EDIT in Sept. 2017:

I have tested the rendering performances described above with QGIS 2.99.0 (I think Version 36). But the problem is still the same as in 2.18.

Is there a possibility to speed up rendering in 3.0?

  • Did you make sure the rendering settings have been set correctly? I.e. from the menubar: Settings > Options > Rendering – Joseph Jan 17 '17 at 12:07
  • What are the correct settings? The first three options (By default new layer..., Use render caching ... and Render layers ...) are marked as true. – vezzon Jan 17 '17 at 12:18
  • Apologies, I meant enabling rendering caching and setting the maximum cores available. – Joseph Jan 17 '17 at 12:20
  • There is no difference to the default settings. QGIS 2.14 is with the default settings very fast! – vezzon Jan 17 '17 at 12:29
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I've noticed this exact problem too. My current solution is to use the LTR 2.14 release of QGIS. I found a bug issue on QGIS bug report related to this problem. There is already a difference between 2.14 and 2.8. But the increased time of rendering in 2.18 make it unusable. http://hub.qgis.org/issues/15752

  • So do I. I step back to 2.14 because 2.18 is unuseable in this case for me. It's a pity because there would be some nice improvments in 2.18. – vezzon Apr 28 '17 at 5:54

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