I've never worked in payments, but I think you can't take too many lessons from trading infrastructure for payments infra due to the way the scaling works.

In trading infra you are dealing with fairly finite number (100s to 10,000s) of instruments trading very large volumes of transactions (thousands to billions), so you can shard by instrument, dedicate CPUs, keep everything in memory and voila. Cross instrument consistency is generally not as much of a problem, depending on what part of the stack you are working on (order book / matching engine / market data feed / order router / position calculations / etc ).

With payments I'd imagine you are dealing with millions of payers, millions of payees, and 10s - 1000s of payments each.