On Feb 25, 2012, at 5:38 PM, Reid Draper wrote: > On Feb 25, 2012, at 8:29 PM, Armon Dadgar wrote: > >> On Feb 25, 2012, at 5:24 PM, Reid Draper wrote: >>>>>> >>>>>> I'm not convinced that a CAS operation is inevitably subject to data >>>>>> races. >>>>>> There are proven techniques for avoiding races at the cost of latency, >>>>>> which is acceptable in certain situations. >>>>> Correct, but as far as I know, there is no way to build a CAS system >>>>> on top of the primitives provided by the Riak public API. You need >>>>> a point of serialization amongst all of the replicas (for a particular >>>>> key), >>>>> which Riak does not provide, for availability reasons. >>>> >>>> I think a point of serialization is not needed here. It should be >>>> sufficient >>>> to add a new internal API for nodes to handle a two-phase commit, and >>>> then the transaction coordinator (running on whatever node you make >>>> the request to) can contain the logic to carry out the transaction. >>> If I understand you correctly, the "transaction coordinator" would >>> be a point of serialization. >> >> Not a global point of serialization, other transactions would be unaffected. >> It is my understanding that there is a new transaction coordinator for >> each client request. So it is already always "serial" in a sense. > > What I'm suggesting you need is a point of serialization for > at least a quorum of the replicas for a particular key. It doesn't > have to be global across the key-space.
Yes, that sounds correct. I think we are saying the same thing. It certainly wouldn't be as performant as doing a non-CAS operation, but for situations where you are willing to make that trade off, it would be nice to have support. > It might be possible to do CAS with replicas without a synchronization > point, but I imagine such a discovery would be publication-worthy. Haha, indeed that would be. _______________________________________________ riak-users mailing list [email protected] http://lists.basho.com/mailman/listinfo/riak-users_lists.basho.com
