Arun Mathew created KAFKA-3643:
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             Summary: Data Duplication on clean restart of Kafka Broker
                 Key: KAFKA-3643
                 URL: https://issues.apache.org/jira/browse/KAFKA-3643
             Project: Kafka
          Issue Type: Bug
          Components: core
    Affects Versions: 0.9.0.1
            Reporter: Arun Mathew


We observed event duplication while partition leadership is restored back to 
preferred leader from the new leader upon restart of the preferred leader.

Steps to Reproduce

- Three Broker Kafka Cluster (B1, B2, B3)
- Create a topic with 3 replica and 1 partition. 
        - [B1 is assigned the (preferred) Leader, B2, B3 are ISR]
- Start sending events using performance producer for large number of events 
that can last for few minutes to cover the broker restart time interval (say 
4Million)
        - set producer batch size = 1
- Clean shutdown Leader Broker B1
        - Event sending continues
        - Now, B2 is the new Leader and B3 is ISR.
- Restart the Broker B1 (preferred leader for Partition 0)
        - The replica in B1 catches up and becomes the Leader for P-0
- Wait for producer to finish
- Use get offset command to get the event count in Partition, which is higher 
than events sent (4M)



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