&gt; Its not like you can throw together some trading system with an eventually consistent datastore in the back. Loosing a couple of trades without an audit trail crashes markets.<p>That&#x27;s not consistency, though, that&#x27;s <i>durability</i>. Consistency in banking is basically the part where you don&#x27;t allow people to spend money twice. That can be &quot;eventual&quot; and violating it can be OK under some circumstances, like when your bank issues you an overdraft (and applies a fee) or when your airline sells too many seats.<p>So the eventually consistent data store in the back is fine... as long as it&#x27;s durable and as long as you&#x27;re willing to invest man-years of effort in understanding the implications of your selected consistency model so that you don&#x27;t screw it up and can perform operations which are compliant with some set of business rules that the business understands and approves of, naturally.