It's the timestamps provided in the columns that do concurrency control/conflict resolution. Basically, the newer timestamp wins. For counters I think there is no such mechanism (i.e. counter updates are not idempotent).
>From https://wiki.apache.org/cassandra/DataModel : All values are supplied by the client, including the 'timestamp'. This > means that clocks on the clients should be synchronized (in the Cassandra > server environment is useful also), as these timestamps are used for > conflict resolution. In many cases the 'timestamp' is not used in client > applications, and it becomes convenient to think of a column as a > name/value pair. For the remainder of this document, 'timestamps' will be > elided for readability. It is also worth noting the name and value are > binary values, although in many applications they are UTF8 serialized > strings. > Timestamps can be anything you like, but microseconds since 1970 is a > convention. Whatever you use, it must be consistent across the application, > otherwise earlier changes may overwrite newer ones. 2012/5/28 Helen <live42...@gmx.ch> > Hi, > what kind of Concurrency Control Method is used in Cassandra? I found out > so far > that it's not done with the MVCC Method and that no vector clocks are > being used. > Thanks Helen > > -- Filipe Gonçalves
