Scrolling attribute table of a layer added with the "delimted text provider" is almost impossible

[gioman]

QGIS 3.14/master, Linux and Windows.

I added a delimited text layer from a 18k rows CSV (so not exactly a big dataset) and scrolling the table of attributes is basically impossible (way too slow, almost now moving, also causing freezes).

I tested the same CSV on 2.18 and it was almost fine (it works except for some hiccup).

[nyalldawson]

I suspect it's related to the recent View Selection performance issue too

[gioman]

@signedav ping just to let you know that this is maybe related to #38018

[signedav]

Hi @gioman I cannot reproduce the issue. Can you provide me the CSV file?

Edit: I tested with a 50k rows on 100 columns but a dummy file with just strings and ints. So maybe it's not representative.

[gioman]

I cannot reproduce the issue.

with or without the latest patch (the revert of the previous patch)?

Can you provide me the CSV file?

sure:

sample_csv.zip

CRS of data is EPSG 32629. For some reason I just noticed that if the table is docked then it is usable (barely considered that it is really a small dataset), while not docked full screen is really unsable. I'm on master on Ubuntu 18.04.

[signedav]

Right now I have the master on that state of last week 4f34b8a with Ubuntu 20.04.
Open the attribute table takes some seconds. Changing the filter leads to the other issue here #38018
But scrolling works fine. Are there other leads? Or can you do a test when you can compile again?

[gioman]

But scrolling works fine.

definitely not working fine here... let me test on other systems.

[gioman]

@signedav adding that CSV as geometryless table (i.e. by d&d the csv on the canvas) results is a quick table, you must add it as delimited text (spatial) table to see the slow down.

[signedav]

Thanks. I can reproduce on master. Haven't found the reason yet.

[signedav]

I checked out the commit c6823d8 what is the last commit of the implementation that contained the reason for #38018 but the scrolling was fine (maybe sometimes minimal hickups - but master lags clearly)
This leads me to the conclusion that these issues are not directly related.

On master I imported the data to a geopackage - means I opened the delimited layer and dragged it into an existing geopackage: The scrolling was fine on this layer. Maybe that's a lead. But I don't know.

[rouault]

Thanks to @nyalldawson live debugging section, it was found this is caused by 644a564 . 99% time is spent in QString::indexOf()