Relativistic systems still behave causally; What observers can't agree on is how much time passes between events. The database is just another observer, so it w

Relativistic systems still behave causally; What observers can't agree on is how much time passes between events. The database is just another observer, so it would commit the transactions in the order that light-rays arrive. The requirement to preserve causality is why there is an upper bound on the speed of information, so that all observers can still agree on the order of events.