The production version of the Hadoop and Cassandra combination needs to go into a separate cluster. The first obvious issue is you probably wouldn't want Hadoop to keep polling Cassandra nodes, hampering Cassandra's performance to end users. The general pattern to avoid this is to split the ring into two data centers. Since Cassandra automatically and immediately replicates the changes between data centers, they will always be in sync. What's more, you can assign one of the data centers as transactional with a higher replication factor and the other as an analytical data center with a replication factor 1. The analytical data center is the one used by Hadoop without affecting the transactional data center.

Now, you do not really need to have two physically separated data centers to make this configuration work. Remember NetworkTopologyStrategy? (Refer to Chapter 3, Effective CQL.) You can tweak Cassandra thinking there are two data centers by just assigning the...