Cassandra Data replication

• Cassandra stores replicas on multiple nodes to ensure reliability and fault tolerance.
• A replication strategy determines the nodes where replicas are placed.
  • total number of replicas across the cluster is referred to as the replication factor.
    • RF 1 → only one copy of each row in the cluster. (one node)
• All replicas are equally important (there is no primary and master replica)

 

Replication strategy

• SimpleStrategy
  • Use only for a single datacenter and one rack.
• NetworkTopologyStrategy (Recommended)
  • use when you have your cluster deployed across multiple datacenters.
  • this strategy specified how many replicas you want in each datacenter.
  • how many replicas to configure in each datacneter?
    • two primary considerations
      • being able to satisfy read locally, without incurring cross data-center latency
      • failure scenarios.
    • Two replicas in each datacenter
      • this configuration tolerates the failure of a single node per replication group and still allows local read at a consistency level of ONE.
    • Three replicas in each datacenter
      • this configuration tolerates either the failure of one node per replication group at a strong consistency level of LOCAL_QUORUM or multiple node failure per datacenter using consistency level ONE.