Problem:
The issue stems from confusion surrounding the Replication Factor (RF) in Apache Cassandra, where the documentation implies RF determines the quantity of data copies, but clarity on this matter is lacking.
Process:
To address this issue, in-depth investigation took place. The team explored the information provided by the client:
- Cassandra Configurations:
- Cassandra Version: 4.0.1
- 6-node cluster.
- 2 Data Centers in the cluster.
- Each DC has 3 nodes of Cassandra.
- RF=3 (indicating all 3 nodes in a data center have a copy).
Solution:
Upon investigation, it is confirmed that in Cassandra 4.1, the number of replicas refers to data copies only, excluding the main chunk. Thus, RF=3 means one main copy and two replica copies, resulting in a total of 3 copies of any chunk of data.
Recommended Configuration:
The advice is to have 1x main chunk and 1x copy (replica) per data center. For a cluster with 6 nodes (3 nodes per data center), RF=3 per data center is considered excessive due to the following reasons:
- Write Performance: More data needs to be written to nodes, impacting write performance.
- Consistent Reads: More nodes are involved in reading data, affecting consistent reads.
- Storage Needs: Additional storage requirements are incurred.
- Data Safety: In the event of a node failure, constructing replicas becomes challenging when there are no more nodes.
The recommended configuration for small clusters remains 1x main copy and 1x replica per data center for optimal performance and safety.
Conclusion:
In conclusion, understanding the nuances of replication factors is crucial for configuring Apache Cassandra effectively. The recommended configuration strikes a balance between performance and data safety, particularly in smaller clusters.