4 ms·

> Secondly, Antirez's argument that you can use a compare & swap in a transactional storage layer is also wrong. This is not possible to write safely. Could yo

• carllerche 11y ago
  In short, either the storage layer provides enough guarantees to ensure safety without redlock OR it is not possible to ensure safety. I believe that antirez's proposal is the former, but if he has a safe algorithm that does not require a linearizable CAS operation in the storage layer and is safe w/ redlock, I would love to hear it. I also provided an example of how to use Cassandra which is eventually consistent safely with a locking service that provides monotonic tokens.
• jamesblonde 11y ago
  Compare and swap has a consensus number of 2. A consensus number is the maximum number of processes for which the object can solve a simple consensus problem. It is impossible to construct a wait-free implementation of an object with consensus number n from an object with a lower consensus number. In other words, test-and-set is weaker than transactions or Paxos for >2 concurrent clients. http://cs.brown.edu/~mph/Herlihy91/p124-herlihy.pdf http://cs.brown.edu/~mph/Herlihy91/p124-herlihy.pdf
  • jhallenworld 11y ago
    Wait, compare and swap has a consensus number of infinite (from Herlihy's paper).
    • jamesblonde 11y ago
      Oops, you're right. I was thinking of test-and-set.