Atomic batches in Cassandra 1.2

In Cassandra 1.2, atomic batches are introduced to ensure that all updates within a batch are completed successfully or not at all. This feature addresses the issue of partially applied batches in case of coordinator failure. However, atomic batches come with a performance cost of about 30% compared to non-atomic batches. To balance between atomicity and performance, Cassandra also provides UNLOGGED BATCH for scenarios where atomicity is not required. Additionally, COUNTER BATCH is introduced for improved performance when updating multiple counters in the same partition. Atomic batches use a new system table called batchlog to record batches until they are successfully written or hinted. The batchlog is node-local and uses StorageProxy for special handling of replication and failure recovery. Cassandra 1.2beta1, which includes atomic batches, is available for download on the Apache site with a projected final release by the end of the year.