But that probability includes the possibility for the first generated message to collide with the last one, and to store that many messages (100k/sec, 2mill ser

But that probability includes the possibility for the first generated message to collide with the last one, and to store that many messages (100k/sec, 2mill servers, 8 bytes/UUID) is 4*10^17 (400 Petabyte) allone. I guess most of the messages created in such a system will be emphemeral...