SimpleStrategy

SimpleStrategy is a replication strategy used by Apache Cassandra to determine how data is replicated across nodes in a cluster. It places replicas on successive nodes around the cluster’s token ring, starting at the token corresponding to the partition key. The number of replicas is defined by the replication_factor setting for the keyspace.

This strategy is designed for single data center deployments. It does not take multiple data centers into account; all replicas are chosen from the same data center. In clusters that span more than one data center, SimpleStrategy can lead to incomplete cross-DC replication and reduced resilience, since replicas are not distributed across multiple data centers.

For multi-data-center deployments, NetworkTopologyStrategy is recommended. It allows explicit specification of how many replicas to place in each data center, improving fault tolerance and latency characteristics by distributing data more evenly across the entire cluster.

Operationally, SimpleStrategy relies on the snitch to identify the local data center, and then selects the first replication_factor nodes in ring order within that DC. It is a straightforward approach and can be adequate for development, testing, or single-DC environments, but it provides no guarantees about cross-DC redundancy or topology-aware placement.

In summary, SimpleStrategy offers a simple, single-DC-aware replication model suitable for uncomplicated deployments. For production systems spanning multiple data centers, NetworkTopologyStrategy provides more predictable replication and resilience.