Most of the time the autocomplete feature in VIM works nicely for me, but sometimes it seems to be scanning files which the current file references, and then it becomes painfully slow, sometimes taking several seconds to release focus back to me.

Sometimes VIM tells me simply that it is "Scanning" other times, it's saying "Scanning tags"

I've only this happen in Ruby files, and it happens mostly when there is a require in the file.

My guess would be that this is some kind of feature which checks related files for autocomplete options, but I don't really need that, and would prefer quicker autocomplete.