Ronning out of Undo

[PhilOfPerth]

Set it to zero and you can't undo anything.

Set it to 1000MB and you'll probably never have an issue, as that stores several hundred undoes, in most cases.

What I meant was, If I change my Undo size to zero, then IMMEDIATELY, reset it to say 1000, is this like flushing the Undo?
(and if so, could this maybe be built into an optional command?) 
If I'm happy with the prog to that point, would this be a reasonable option?