I'm in a pseudo-deadlock about Cassandra and atomicity/isolation/transaction arguments. My simple question is: what happens when two (or more) threads try to update (increment) the same integer column value of the same row in a column family? I've read something about row-level isolation, but I don't sure that is managed properly. Any suggestions? (N.B. The updates requires a read of current value before the update write. Otherwise counter column can be used, but in my opinion the problem still remain).
My personal idea is described next. Because it's a real time analytics application, the counter updates are inherent only the current hour, while previous hours still remain the same. So I think that one way to avoid the problem should be to use a RDBMS layer for current updates (which support ACID properties) and when the hour expires consolidate data on Cassandra. It's right? Also in the case of RDBMS layer still remain the transaction problem: some update on different column family are correlated and if even one fails a rollback is needed. I know that Cassandra doesn't support transactions, but I think that, playing with replication factor and write/read levels the problem can be mitigated, eventually implementing an application level commit/rollback. I read something about Zookeeper, but I guess that add complexity and latency.
