mirror of https://github.com/apache/kafka.git
b73e31eb15
Introduces v2 of Vote RPC and implements the handling of the new version of the RPC. Many references to "candidate" in the Vote RPC are changed to the more generic "replica". Replicas sending Vote request with PreVote set to true are not candidate. They are instead prospective candidate that are attempting to become candidate. Replicas receiving PreVote requests (vote request with PreVote=true) with an epoch equal to their own will _not_ transition to Unattached state. They will only grant the vote if they have not recently fetched from leader and the request's last epoch and offset are up-to-date with theirs. If a replica receives a PreVote request with an epoch greater than their current epoch, they will transition to Unattached state (setting their epoch to the one from the pre-vote request) and then grant the vote if the request's last epoch and offset are up-to-date with theirs. To avoid a possible ping-pong scenario. For example, there is 3 node quorum, leader node A disconnects from quorum, node B goes into prospective state first before node C, node B sends pre-vote request to node C still in follower state and receives back that node A is leader, node B transitions to follower while node C transitions to prospective after election timeout. If you repeat this interaction, it is possible for such replicas to transition from Follower to Prospective in perpetuity. This issue is resolved by having follower state nodes grant pre-vote requests only if they have successfully fetched from the leader at least once after becoming a follower. This change introduces a new suite called KafkaRaftClientPreVoteTest, for additional KRaft protocol tests with respect to pre-vote. Reviewers: José Armando García Sancio <jsancio@apache.org> |
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