Hi Daniel,

TypeSystem paclet version 12.1.0.2 did improve Dataset performance for the datasets I am working with, especially rendering. However, it did introduce this bug.

I do not know whether this is pure imagination - I have no values on prior performance - but I do have the strong impression that in the meantime Dataset[] has greatly improved! Could that be?

I believe there was confirmation in the MSE chat. To the best of my knowledge the UI issues with Dataset are the top priority for improving in the near term.

In[69]:= $Version
Out[69]= "12.1.0 for Linux x86 (64-bit) (March 14, 2020)"

Yes - incredible but true: If one let simply e.g.

ResourceData[ResourceObject["Epidemic Data for Novel Coronavirus COVID-19"]]

pop up in a notebook one virtually can no longer work with this Mathematica session - and this data set is just of moderate size. Everything is then drastically slowed down - even the window showing the Documentation Center! The slightest interaction makes the CPU busy for many seconds. At the moment I would qualify Dataset simply as unusable and I am puzzled how a function like this can be released! Hopefully this will be fixed soon - please!

Additional note:

I do not want to switch back to v12.0 because for this version I had reported a problem regarding Dicom import - and this is actually fixed in 12.1. Thus for me this is definitely an improvement and it would not be fair not to mention this.

I try to have some empathy with new releases as I know the pain they can be. However, sometimes it seems there's just no Q&A. This literally makes Dataset unusable for time series data. How could this slip past Q&A? I can confirm it happens in both Mac and Windows.