Subsequent selections kill QGIS ui performance

[rduivenvoorde]

When creating a selection in a rather large dataset, the first time is pretty fast.

BUT if you then change the way of selecting (for example change from select by Value to select by Expression) THEN Qgis stalls.

How to Reproduce

• download the osm-line gpkg from https://www.dropbox.com/sh/kfj9bptiiwjccqe/AADGppvIBEoztMeh5RP_FUlxa?dl=0
• now create a selection by Expression with "railway"='rail' Result: fast selection of 28000 features
• now switch to 'select by Value' (while the old selection is still visible)
• this result in... QGIS stalling/freezing and the normal select by Value dialog does nog show up.
• it will take A LONG time for the dialog to show
• NOTE: when you stay with the SAME way of selecting (say selecting by Expression twice), there is NOT slow dialog popup

Is QGIS at that moment 'unselecting' the earlier selection? Or... what is it that QGIS is busy with?

Running 3.16 or master on Linux

[gioman]

O yeah, confirmed here too on master.

[rduivenvoorde]

I'm going to try Hotspot as Nyall was showing in his bugfixing video:
https://youtu.be/du5DSWik3V4?t=4562

Mmm, using Hotspot appimages (both latest and nightly) crash as soon as I try to attach to running QGIS.
Tried compiling myself but would need to install kdab dock widgets from external repo, which I prefer not to do...
@nyalldawson how did you manage this?

[elpaso]

When creating a selection in a rather large dataset, the first time is pretty fast.

BUT if you then change the way of selecting (for example change from select by Value to select by Expression) THEN Qgis stalls.

How to Reproduce

* download the osm-line gpkg from https://www.dropbox.com/sh/kfj9bptiiwjccqe/AADGppvIBEoztMeh5RP_FUlxa?dl=0

* now create a selection by Expression with "railway"='rail' Result: fast selection of 28000 features

* now switch to 'select by Value' (while the old selection is still visible)

* this result in... QGIS stalling/freezing and the normal select by Value dialog does nog show up.

* it will take A LONG time for the dialog to show

* NOTE: when you stay with the SAME way of selecting (say selecting by Expression twice), there is NOT slow dialog popup

Is QGIS at that moment 'unselecting' the earlier selection? Or... what is it that QGIS is busy with?

Fetching features by id (the ids of the previously selected features).

[rduivenvoorde]

@elpaso is that needed to be able to (optionally) merge the new selection to the old one?

So you think adding an index on the id (if available) would help? Will try it now...
OR is it just busy with fetching these 27000 (rather large, a lot of attributes) features, and an index would not be helpfull? If so would cleaning up this osm data (eg removing a lot of attributes) help?

AND another question to me: why does this behaviour only show when you change the way to do the selection, and NOT when you keep the same?

[elpaso]

@elpaso is that needed to be able to (optionally) merge the new selection to the old one?

So you think adding an index on the id (if available) would help? Will try it now...

No, it won't help for the reason you mention below and I'm pretty sure GPKG already has an index on the fid.

OR is it just busy with fetching these 27000 (rather large, a lot of attributes) features, and an index would not be helpfull? If so would cleaning up this osm data (eg removing a lot of attributes) help?

AND another question to me: why does this behaviour only show when you change the way to do the selection, and NOT when you keep the same?

Sorry, I'm busy on other issues and I only had time for a quick debug run yesterday evening, the only evidence I have so far is that it gets stuck on retrieving every single feature individually by id, because of the existing selection.

I'll see if I can have a closer look later.

[nyalldawson]

I'll take a look if you want @elpaso?

[elpaso]

I'll take a look if you want @elpaso?

Yes, please 😃