[Qgis-user] Diagnosing QGIS slowdown (Windows)

[Martin Pergler]

Happy user of QGIS since about 3.2. Currently using 3.16.1 (OSGeo4W install)
and experiencing pretty severe performance degradation. I know these things
are a bear to hunt down; would appreciate any suggestions how to go about
finding the cause of the problem.

Symptoms:
- Mild sluggishness rendering canvas with editing turned off, as well as
general UI operations (e.g. tooltips on layers in layer list sometimes first
appear as a black box, and only 1/2s later fill with the actual tooltip)
- Mild sluggishness digitizing new lines or vertex-editing new ones
- Significant slowdown in attribute form for new features digitized (2-3s
response time to type in a text field, for instance)
- When attribute form closed, prior features in layer being edited sometimes
fail to be rendered on canvas (the new one just added is)
- 10-15s freeze (blue circle mouse icon) after exiting edit mode. Edits are
saved properly.

Things worked just fine on the same project until last month, when I took a
break from GIS tasks. In between, I both upgraded 3.16.0 -> .1, as well as a
new Windows OS update installed itself, and some new device drivers. So
plenty of things to blame.

I have already:

1. Uninstalled and reinstalled OSGeo4W completely

2. Tried with a new, no-plugin user profile (sluggishness persists, though a
bit better - so I suspect some low-level slowdown which struggles with
anything additional, but is not directly caused by something in my profile)

3. Checked I have all layers indexed, no crazy validation rules, etc. BTW
all my layers are in a gpkg (or raster TIFFs) on a local drive (and besides
it worked before).

4. Monitored hardware performance. I have adequate hardware for QGIS. CPU
usage stays ~30%, GPU ~20%, temperatures reasonable, RAM usage reasonable.

5. Tried disabling the Browser panel (given some recent bug reports on
Browser and network drives). No effect.

Thanks for any sleuthing suggestions!




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