So, regarding transactions, absolutely you can throw them away on cancellation. But there's an interesting wrinkle here: if you use a connection pool like most users, and you were going to do the ROLLBACK at the end of your future on error, then that ROLLBACK wouldn't run it the future is cancelled! Then future operations reusing the same connection would be stuck in transaction la-la land.

(This is related to the fact that Rust doesn't have async drop — you can't run async code on drop, other than spawning a new task to do the cleanup.)

This is prong 3 of my cancel correctness framework (that the cancellation violates a system property, in this case a cleanup property.) The solution here is to ensure the connection is in a pristine state before handing it out the next time it's used.