Replication across data centers

In the previous chapters, we touched on the idea that Cassandra can automatically replicate across multiple data centers. There are other systems that allow similar replication; however, the ease of configuration and general robustness set Cassandra apart. Let's take a detailed look at how this works.

Setting the replication factor

You will recall from Chapter 3, Replication, that specifics about replication are configured via CQL at the keyspace level. Since we're on the topic of multiple data centers, it's important to understand that you'll always have to use the NetworkTopologyStrategy, since the SimpleStrategy does not allow you to set replication factor for each data center.

Using our example physical topology from the PropertyFileSnitch section, the following statement will create a keyspace, users, with three replicas in each of our two live data centers, as well as one in the analysis data center:

CREATE KEYSPACE users
  WITH REPLICATION...