"The main downside of this is the fact that object storage doesn't have transactions, so you can't make sure that both appending the event and updating the stat

"The main downside of this is the fact that object storage doesn't have transactions, so you can't make sure that both appending the event and updating the state of the world happen in one atomic unit. We write the state first and the event second, so a process dying in between leaves the state correct and the history missing an entry. Nothing detects that, because detecting it would mean something reads the log and compares it to state, and the entire point is that nothing does. So every entry in the log really happened. What you don't get is a guarantee that everything that happened is in it." So, they built a thing that pretends to, but does not actually properly handle transactions? I guess I should be glad they are not a fintech startup...