No, I didn't check first - but EDIT: "compress" did seem to do the trick....sort of.
Also no, I didn't back up the database (I will from now on). I am 73, retired and I'm usually gardening with a rum & coke, or reading with a rum & coke - much too lazy to back up stuff.
But I have learned my lesson and will be backing up the DB every time I plug in my Clara.
I kinda thought the compress command shouldn't take too long, but since I've never done it before, I figured I should ask. I suppose Calibre did get hung up somehow.
Thanks for the reply.