I am pretty new to distributed systems and was wondering how Raft consensus algorithm is linearizable. Raft commits log entries through quorum. At the moment the leader Raft commits, this means that more than half of the participants has the replicated log. But there may be a portion of the participants that doesn't have the latest logs or that they have the logs but haven't received instructions to commit those logs.
Or does Raft's read linearizability require a read quorum?
Well, linearizability pertains to both reads and writes, and yes, both are accomplished with a quorum. To make reads linearizable, reads must be handled by the leader, and the leader must verify it has not been superseded by a newer leader after applying the read to the state machine but before responding to the client. In practice, though, many real-world implementations use relaxed consistency models for reads, e.g. allowing reads from followers. But note that while quorums guarantee linearizability for the Raft cluster, that doesn’t mean client requests are linearizable. To extend linearizability to clients, sessions must be added to prevent dropped/duplicated client requests from producing multiple commits in the Raft log for a single commit, which would violate linearizabity.