ScyllaDB’s Safe Topology and Schema Changes on Raft

ScyllaDB has transitioned to using the Raft consensus algorithm for managing all topology and schema metadata, enhancing elasticity, operability, and performance. This shift to strong consistency enables safe, concurrent, and rapid cluster bootstrapping and topology changes, with a centralized topology coordinator overseeing these processes. The move from an eventually consistent model, which was initially adopted for its compatibility with Cassandra, to a strongly consistent model for metadata ensures reliable and automated node operations and cluster scaling. ScyllaDB 6.0 has expanded its use of Raft to include schema and topology changes, authentication, service levels, and CDC stream details, improving data availability and eliminating previous reliance on the Gossip protocol. Additionally, the new design introduces a dedicated metadata commit log, linearizable schema versioning, and automated SSTable cleanup, while providing enhanced manageability through new system tables, REST APIs, and a maintenance mode. The integration of Raft facilitates extreme elasticity and serves as the foundation for ScyllaDB's new tablets architecture, highlighting improvements in cluster performance and management.