| The reasoning required is the same in both cases. To avoid serialization conflicts you still have to identify all those appropriate records and appropriate times in your reasoning. Well, sort of. Serializability allows you to reason locally for correctness, but not for performance. That is, however, a meaningful distinction. Serializability remains a marked improvement over the status quo. Most operations aren't actually performance sensitive, so that tradeoff makes perfect sense. With serializability, we need only focus our efforts on those operations which are both performance sensitive and highly contended. This has nice emergent properties, because the problematic transactions are immediately apparent: they are the slow ones, the ones that are not meeting their performance budget. Performance anomalies are directly measurable and immediately visible. Correctness anomalies are generally neither. Performance anomalies are generally localized and ephemeral. Correctness anomalies are often persistent and viral. So the choice is either to explicitly implement required locking for RC or let the SERIALIZABLE do it implicitly under the hood (and hoping that it will do it better :). Again, when it comes to correctness, there's no real hope to do better than serializable. When it comes to performance: sure. But in every application domain I've worked, getting to a wrong result faster is rarely useful. (I understand that this is not a universal truth, but I believe it is significantly more common than the alternative. The adage "first make it work, then make it fast" comes to mind.) in my experience any non-trivial system wouldn't run in SERIALIZABLE without hitting the conflicts until the system gets subjected a lot to that "global reasoning" that you mentioned. I agree that there have been (and still are) practical impediments to deploying large-scale serializable systems with incumbent technologies. But I disagree that those impediments are inherent to all implementations of the serializable isolation level, which is why these kinds of articles (and the R&D behind them) are so important. We still have a long way to go before serializable-by-default is a tenable option for the most demanding of systems, but that is what we should be working towards. |