Hi Paul, about the last answer I still need some more clarifications, as I understand it if QUORUM is used, then reads doesn't get old values either? Or am I wrong? Thank you very much! Best regards, Daniel.
2010/4/21 Paul Prescod <pres...@gmail.com> > I'm not an expert, so take what I say with a grain of salt. > > 2010/4/21 Даниел Симеонов <dsimeo...@gmail.com>: > > Hello, > > I am pretty new to Cassandra and I have some questions, they may seem > > trivial, but still I am pretty new to the subject. First is about the > lack > > of a compareAndSet() operation, as I understood it is not supported > > currently in Cassandra, do you know of use cases which really require > such > > operations and how these use cases currently workaround this . > > I think your question is paradoxical. If the use case really requires > the operation then there is no workaround by definition. The existence > of the workaround implies that the use case really did not require the > operation. > > Anyhow, vector clocks are probably relevant to this question and your next > one. > > > Second topic I'd like to discuss a little bit more is about the read > repair, > > as I understand is that it is being done by the timestamps supplied by > the > > client application servers. Since computer clocks (which requires > > synchronization algorithms working regularly) diverge there should be a > time > > frame during which the order of the client request written to the > database > > is not guaranteed, do you have real world experiences with this? Is this > > similar to the casual consistency ( > > http://en.wikipedia.org/wiki/Causal_consistency ) .What happens if two > > application servers try to update the same data and supply one and the > same > > timestamp (it could happen although rarely), what if they try to update > > several columns in batch operation this way, is there a chance that the > > column value could be intermixed between the two update requests? > > All of this is changing with vector clocks in Cassandra 0.7. > > https://issues.apache.org/jira/browse/CASSANDRA-580 > > > I have one last question about the consistency level ALL, do you know of > > real use cases where it is required (instead of QUORUM) and why (both > read > > and write)? > > It would be required when your business rules do not allow any client > to read the old value. For example if it would be illegal to provide > an obsolete stock value. > > > Thank you very much for your help to better understand 'Cassandra'! > > Best regards, Daniel. > > >
