It gets complex. There are a lot of tradeoffs between short and long running transactions, and different choices in the design space each have pluses and minuse

It gets complex. There are a lot of tradeoffs between short and long running transactions, and different choices in the design space each have pluses and minuses. Of course if you're running reduced consistency things are easier. Wrong answers are often faster. But when people select a transactional database, it's usually because they at least need snapshot consistency, and often they require full serializability.