Yes, but the value is supposed to be 11, since the write failed. On Mon, Nov 22, 2010 at 2:27 PM, André Fiedler <fiedler.an...@googlemail.com > wrote:
> Doesn´t sync Cassandra all nodes if the network is up again? I think this > was one of the reasons, storing a timestamp at every key/value pair? > So i think the response will only temporary be 11. If all nodes have synct > it should be 12? Or isn´t that so? > > greetings André > > 2010/11/22 Samuel Carrière <samuel.carri...@gmail.com> > > >Cassandra can work in a consistent way, see some of this discussion and >> the Consistency section here >> http://wiki.apache.org/cassandra/ArchitectureOverview >> > >> >If you always read and write with CL.Quorum (or the other way discussed) >> you will have consistency. Even if some of the replicas are temporarily >> inconsistent, or off line or whatever. Your reads will >be consistent, i.e. >> every client will get the same value or the read will not work. If you want >> to work at a lower or higher consistency you can. >> > >> >Eventually all replicas of a value will become consistent. >> > >> >There are a number of reasons why cassandra may not be a good fit, and I >> would guess something else would be a problem before the consistency model. >> > >> >Hope that helps. >> >Aaron >> >> Hello, >> >> I like cassandra a lot and I'm sure it can be used in many use cases, >> but I'm not sure we can say that we have strong consistency, >> even if we read and write with CL.Quorum. >> >> Firstly, we can only expect consistency at the column level. Reading >> and writing with CL.Quorum gives you most of the time >> a consistent value for each individual column, but it does not mean if >> gives you a consistent view of your data. >> (Because cassandra gives you no isolation and no transactions, your >> application has to deal with data inconsistencies). >> >> Secondly, I may be wrong, but I'm not sure consistency at the column >> level is guaranteed. Here is an example, with a replication >> factor of 3. >> Imagine that the current value of col1 is 11. Your application tries >> to write "col1 = 12" with CL.Quorum. >> Imagine the write arrives to node 1, but that the new value is not >> transmitted to nodes 2 and 3 because of network failures. So >> the write fails (this is the expected behaviour), but node 1 still has >> the new value (there is no rollback). >> >> Then, imagine that the network is back to normal, and that another >> client asked for the value of col1, with CL.Quorum. Here, >> the value of the response is not guaranteed. If the client asks for >> the value to node 2 and node 3, the response will be 11, but >> if he asks to node 1 and node 2 or 3, the response will be 12. >> >> Am I missing something ? >> >> Samuel >> > >
