I don't think that "leave dangling locks" is obviously a possibility from rollback failing. What's the method to clean up those locks? Rollback harder? Commit?

I don't think that "leave dangling locks" is obviously a possibility from rollback failing. What's the method to clean up those locks? Rollback harder? Commit? If a transaction is ever aborted and there's a chance that locks specific to the transaction (MVCC locks necessary for transactional semantics) are still held then it would be safest to always issue this mythical "clean up locks" statement after every rollback attempt. The default final state of a transaction that is not explicitly committed (and even autocommit is still explicit) is that it is aborted, purely because the only way a transaction can be committed is by commiting it vs there are an infinite number of ways and reasons for the transactions to abort. If the rollback is successful or not there is logically no way that the state of the transaction after rollback being invoked is that the transaction is still usable for something.