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Copycat is a feature complete, fully asynchronous implementation of the Raft consensus algorithm in Java 8 designed for use in Atomix. The implementation provides a fully featured client and server and includes:
- Pre-vote election protocol (§4.2.3)
- Session-based linearizable writes (§6.3)
- Lease-based fast linearizable reads from leaders (§6.4.1)
- Fast sequential reads from followers (§6.4.1)
- Sequential consistency for concurrent/asynchronous operations from a single client
- Session-based state machine events (§6.3)
- Membership changes (§4.3)
- Log compaction via cleaning (§5.3)
Additionally, this implementation has undergone extensive Jepsen testing to verify it maintains linearizability in a number of different failure scenarios.
For more information on the Raft implementation itself, see Raft internals
Copycat is a fault-tolerant framework that provides strong consistency guarantees, and as such we take the responsibility to test these claims and document the implementation very seriously. Copycat's implementation of the Raft consensus algorithm is well tested, well documented, and verified by Jepsen. But the beta label indicates that the implementation may still have some bugs or other issues that make it not quite suitable for production. Users are encouraged to use Copycat in development and contribute to the increasing stability of the project with issues and pull requests. Once we've reached consensus on the lack of significant bugs in the beta release(s), a release candidate will be pushed. Once we've reached consensus on the stability of the release candidate(s) and Copycat's production readiness, a full release will be pushed.
It's all about that consensus!
Documentation for most of Copycat's implementation of the Raft algorithm is available on the Copycat website, and users are encouraged to explore the Javadoc which is also heavily documented. All documentation remains under continued development, and websites for both Copycat and Atomix will continue to be updated until and after a release.
The Atomix project is a collection of standalone Copycat StateMachines and proxies that can be
multiplexed on a single Raft replicated log.