[firebacon]

That only seems possible if both processes were running on the same physical machine (and hence share the same input MAC address).

It's a nasty corner case, but I'm sure the UUID designers considered it a valid tradeoff, since I believe the algorithm was designed for a distributed scenario. In the single-machine case an atomic counter would be a much easier solution with very reasonable efficiency anyway. Still, it might have been clever to also include the local process id in the UUID, I wonder why they didn't to that.

At any rate the problem is easily worked around by running the two processes on different machines, i.e. ensuring you have at most one UUID generating process per host (with respect to the database table in question).