[tracker1]

Scaling financial transactions requires real sharding, but you can't eliminate ACID from the mix... certain functionality just doesn't work like that.

In the end, one system needs to be responsible for a given account... best case you could have is only some accounts/users are affected. It's a different kind of problem.

Facebook, for example uses Cassandra with a very wide distribution of nodes, with an immediate ack on receive... you can't do that with a bank... transactional payment systems won't tolerate it. You could do a few things to alleviate this issue... read-only replicas, etc... even then it's a matter of failing soft (disabling only those systems/services that are unavailable instead of the whole thing).