Yes, Sylvain, you are correct. When I say "A comes before B", it means client will secure the order, actually, B will be sent only after get response of A request.
And Yes, A and B are not update same record, so it is not typical Cassandra consistency problem. And Yes, the column name is provide by client, and now I use the local timestamp, and local time of A and B are not synchronized well, so I have problem. So what I want is, Cassandra provide some information for client, to indicate A is stored before B, e.g. global unique timestamp, or row order. 2013/1/17 Sylvain Lebresne <sylv...@datastax.com> > I'm not sure I fully understand your problem. You seem to be talking of > ordering the requests, in the order they are generated. But in that case, > you will rely on the ordering of columns within whatever row you store > request A and B in, and that order depends on the column names, which in > turns is client provided and doesn't depend at all of the time > synchronization of the cluster nodes. And since you are able to say that > request A comes before B, I suppose this means said requests are generated > from the same source. In which case you just need to make sure that the > column names storing each request respect the correct ordering. > > The column timestamps Cassandra uses are here to which update *to the same > column* is the more recent one. So it only comes into play if you requests > A and B update the same column and you're interested in knowing which one > of the update will "win" when you read. But even if that's your case (which > doesn't sound like it at all from your description), the column timestamp > is only generated server side if you use CQL. And even in that latter case, > it's a convenience and you can force a timestamp client side if you really > wish. In other words, Cassandra dependency on time synchronization is not a > strong one even in that case. But again, that doesn't seem at all to be the > problem you are trying to solve. > > -- > Sylvain > > > On Thu, Jan 17, 2013 at 2:56 AM, Jason Tang <ares.t...@gmail.com> wrote: > >> Hi >> >> I am using Cassandra in a message bus solution, the major responsibility >> of cassandra is recording the incoming requests for later consumming. >> >> One strategy is First in First out (FIFO), so I need to get the stored >> request in reversed order. >> >> I use NTP to synchronize the system time for the nodes in the cluster. (4 >> nodes). >> >> But the local time of each node are still have some inaccuracy, around 40 >> ms. >> >> The consistency level is write all and read one, and replicate factor is >> 3. >> >> But here is the problem: >> A request come to node One at local time PM 10:00:01.000 >> B request come to node Two at local time PM 10:00:00.980 >> >> The correct order is A --> B >> But the timestamp is B --> A >> >> So is there any way for Cassandra to keep the correct order for read >> operation? (e.g. logical timestamp ?) >> >> Or Cassandra strong depence on time synchronization solution? >> >> BRs >> //Tang >> >> >> >> >> >
