Replication

Cassandra is able to automatically keep multiple copies of data on multiple nodes, hence providing no single point of failure. The number of copies it will create is configurable and determined by a configuration option called a replication_factor. While defining a keyspace, we mention its replication_factor function. This configuration option is applied to all column families of that keyspace. Let's suppose that column family users, which we discussed in the section Data distribution, are part of the keyspace called cassandrademodb; and replication_factor of the keyspace is 3, then every row of the column family users will have three replicas copied to three different nodes. All replicas are the same and there is no primary or secondary replica. First, replica placement is decided by the partitioner and subsequent replicas are placed on consecutives nodes in clockwise order. Cassandra tries not to have two replicas on the same rack while doing so for rack-aware strategies, using...