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If none of the in-sync replicas are alive, the controller allows the user to elect a replica that was not a part of the in-sync replica set using the unclean leader election strategy. Since this new leader replica was not a part of the last known in-sync replica set, there is the possibility for data loss by deleting log records committed by the previous leader(s). In addition, the lost of loss of these records can cause some inconsistency with other parts of the system like the transaction coordinators and the group coordinators. If the controller is able to communicate to the new topic partition leader that it was elected using unclean leader election, the new topic partition leader can coordinate this recovery and mitigate these inconsistencies.

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