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In addition to a replica ID each replica assigned to a KRaft topic partition will have a replica UUID. This UUID will be generated once and persisted as part of the quorum state for the KRaft topic partition. A replica (controller and broker) may host multiple topic partition in multiple log directories. The replica UUID will be generated per topic partition hosted by the replica.

Replicas in a KRaft topic partition that are voter or can become voters will be identified by their ID and UUID.

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Voters are added to the cluster metadata partition by send sending an AddVoter RPC to the leader. For safety Kafka will only allow one voter change operation at a time. If there are any pending voter change operations the leader will wait for them to finish. If there are no pending voter change operations the leader will write a AddVoterRecord to the log and immediately update its in-memory quorum state to include this voter as part of the quorum. Any replica that replicates and reads this AddVoterRecord will update their in-memory voter set to include this new voter. They Voters will not wait for these records to get committed before updating their voter set.

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