You don't need (db) transactions

- 5-6% slower is a small price to pay for correctness. You should be able to "get back" that 5-6% somewhere else.

- This is an exceptionally simple example. What if there are multiple updates, conditionally executed?

- What if your cleanup code fails?

- What if you have a more complex example and your correspondingly more complex cleanup code fails?

- What if your cleanup code for failed cleanup code fails?

- How are you going to write more complex code, with multiple updates conditionally executed, if concurrent activity is changing some of the data you are relying on while you are working on it? In other words, if you bothered to write invariants, they might not hold, even if your code, running in isolation, maintains those invariants.

- Are you giving up on triggers? Triggers may generate updates that aren't even visible in your code. How are you going to back those out?