Yeah, sorry, I assumed log/journal plus reapply-on-recovery went without saying. You can't have guaranteed durability (short of blockchain-style distributed stores) because it's always possible for your database server to suffer a unrecoverable hardware failure between transmitting "transaction success" and taping out its weekly backup. If all else success, your datacenter catching fire and burning down would suffice. So it's only ever a matter of reducing (not eliminating) the probability of having to roll back commited transactions. (Tldr: fsync can't help if your hard drive melted.)