The Raft consensus algorithm is a fault-tolerant consensus algorithm for managing a replicated log. It was designed to be more understandable than Paxos, which was previously the most widely used consensus algorithm.
In Paxos, a single algorithm is used both for electing a leader and for achieving consensus. On the other hand, in Raft, leader election and log replication are separate subproblems. This makes the algorithm easier to understand and implement, since the two subproblems can be tackled separately.
In Raft, a leader is elected via a randomized timeout mechanism. The leader is responsible for managing the state of the replica servers and coordinating with other servers to ensure that the replicated logs are consistent across all servers. Raft uses a leader-based approach, which means that client requests are forwarded to the leader, which in turn replicates the request to other servers.
Raft also maintains a commit index, which ensures that all committed entries in the log are safe and will not be lost. If a majority of the servers have acknowledged a log entry, the leader can consider it committed and may apply it to its state machine. This ensures consistency across all servers.
One notable feature of Raft is its emphasis on simplicity and understandability. The algorithm was designed to be understandable to students and researchers in a short amount of time. Additionally, the algorithm is modular, making it easier to understand and implement. For example, the leader election and log replication modules can be implemented independently, which simplifies the implementation process.
In comparison to Paxos, Raft has demonstrated a higher level of understandability and ease of implementation. The separation of leader election and log replication, along with the emphasis on modularity, makes the algorithm easier to reason about and reason about its correctness. However, Paxos is more widely studied and has more extensive literature available, which may make it easier to find existing code or resources to learn from. Ultimately, the choice between Raft and Paxos may depend on factors such as the specific problem being addressed and the preferences of the development team.