Eh. Deadlocks can be avoided if you don’t use sql’s exact semantics. For example, foundationdb uses mvcc such that if two conflicting write transactions are committed at the same time, one transaction succeeds and the other is told to retry.

It works great in practice, even with a lot of concurrent clients. (iCloud is all built on foundationdb).

Hold & lock is what causes deadlocks. I agree with you - that would be a bad way to implement filesystem transactions. But we have a lot of other options.