Re: [PATCHES] Patch for UUID datatype (beta)

"Harald Armin Massa" <haraldarminmassa@gmail.com> writes:
> They also talk about a "guaranteed differentness" - and as much as I
> understand, they are Unique as long as the MAC-Adresses of the Network-Cards
> are unique, and fall back to "extremly likely" when there is no network card
> present.

MAC addresses are not guaranteed unique (heck, on Apple machines they're
user-assignable, and I think you can change 'em on Linux too).  Another
unrelated-to-reality assumption in the above claim is that the local
system clock is always accurate (is never, say, set backwards).

You can have a reasonably strong probability that UUIDs generated per spec
within a single well-run network are unique, but that's about as far as
I'd care to believe it.
        regards, tom lane