It can be a pain when you do large random deletes from browsing history, then sync can hang up for 20 minutes with lot of IO/Cpu. You can trigger this by doing "Forget this website" and if that website is a lot in your history
I suppose it probably has to rewrite your entire history in that case? Deleting lines in log-like files isn't exactly easy. Actually, I wonder how that's stored in order for the search to stay responsive, some kind of bloom filter? Or just a normal database?
i think they use sqlite for everything
Most browsers use a SQL database for storing data like this.