Not the parent commenter, but I also tried it a year or two ago and my recollection is that I had a similar experience. I have a really long history file that dates back like a decade and if remembering correctly I tried to import it, and it made using my shell very laggy so I ended up removing it. I'm not 100% positive that I'm remembering the exact way that I started experiencing the lag though, so if I have time tomorrow I'll try it out again and see if it's still something I encounter.
Ahh yes, we’ve done a lot of performance optimisation since then. We regularly test on >1m records and have no issues
Make sure you’re using the daemon (the install script will handle this) and you should be good to go
Very happy to help if you have any problems. Ellie at Atuin dot sh
Good to hear! Sounds like my history file might not even be that large compared to your tests now