In Paul Beach's paper "InterBase and the Oldest Interesting
Transaction", he mentions a scenario where a sweep does not
improve performance and at the end explains that this is
because the sweep does not work if there is a "transaction left
permanently open".

What would cause this? Shouldn't transactions be
automatically rolled back on a disconnect?

If they're not, how do you commit them short of
doing a backup/restore?

I also don't understand what he means by not 'rolling
back transactions unnecessarily' and how this would
help prevent said problem.