What’s Next on ScyllaDB’s Path to Strong Consistency

ScyllaDB is advancing its path to strong consistency by introducing Raft-based consistent and centralized topology management in its Open Source 5.4 release, aiming to address limitations like the inability to perform more than one topology operation at a time and the risk of lost writes during topology changes. The new approach eliminates the dependence on ring delay and introduces a centralized topology change coordinator, which drives all topology changes alongside the Raft cluster leader, ensuring that state changes are strongly consistent and can be executed safely and quickly. This implementation includes a new feature called "fencing," which ensures that reads and writes are signed with the current topology version to prevent outdated or incompatible operations, thus resolving consistency anomalies and enhancing the reliability of topology changes. Additionally, the system now supports automatic coordinator failover, ensuring that topology changes can progress even if the coordinator fails, as a new coordinator can take over seamlessly. The changes aim to make topology operations more efficient, reliable, and less prone to operator errors, while the ScyllaDB community looks forward to enhanced scalability and fault tolerance.