This would not work for a exchange. What I work with is an UCITS mutual funds system. Once per day, we get a new price for each fund (the NAV, Net Asset Value). We now need to settle all orders, subscriptions and redemptions, waiting for that NAV. This is of course time critical, but not in the millisecond-sense: As long as it is done within an hour or two, it is all ok.

I believe this holds for very many business processes. If you get a new shipment of widgets, and you can now fulfill your orders waiting for those widgets, it does not really matter if it takes 1 second, or in a very bad outlier day, occasionally 2 hours.

Realize that the point is that this settling, or order fulfillment, will go as fast as possible. Usually within seconds or maybe minutes. However, if you suddenly get a large influx, or the database goes down for a few minutes, this will only lead to a delay - there is nothing you need code up extra to handle such problems. Also, you can scale this very simply, based on what holds you back (services, or database, or other external systems, or IO). It will not be the messaging by itself!