> So you don't see a problem with the behaviour of check constraints at
> the moment?

I am not against any useful feature. If you have some suggestion
how check constraints could be enhanced just tell us.
Don't worry how much you know abou implementation - somebody
who knows enough will say whether such proposal is feasible or not.
(and sometimes even discussion about feature that can't work
can lead to better ideas that will)

In each case it will be better to start by exact defining the problem
and specifying required behaviour than by directly suggesting
solution (e.g. dirty-reads).

Ivan