Bingo. Banks aren't ACID at all. In actuality, the datastore of record for internal bank transactions usually looks more like a continuous transaction journal w

Bingo. Banks aren't ACID at all. In actuality, the datastore of record for internal bank transactions usually looks more like a continuous transaction journal with two account numbers and an amount. The snapshot balance of any account isn't much more than a cache computed value. There are, of course, layers and layers of complex systems built on-top of this, but the actual base of all of it is very simple, old school, batch process technology. The original eventual consistency.