[jira] [Created] (KAFKA-7122) Data is lost when ZooKeeper times out

["Nick Lipple (JIRA)" <ji...@apache.org>]

Nick Lipple created KAFKA-7122:
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             Summary: Data is lost when ZooKeeper times out
                 Key: KAFKA-7122
                 URL: https://issues.apache.org/jira/browse/KAFKA-7122
             Project: Kafka
          Issue Type: Bug
          Components: core, replication
    Affects Versions: 0.11.0.2
            Reporter: Nick Lipple


Noticed that a kafka cluster will lose data when a leader for a partition has their zookeeper connection timeout.

Sequence of events:
 # Say broker A leads a partition followed by brokers B and C
 # A ZK node has a network issue, happens to be the node used by broker A. Lets say this happens at offset X
 # Kafka Controller immediately selects broker C as the new partition leader
 # Broker A does not timeout from zookeeper for another 4 seconds. Broker A still thinks it is the leader, presumably accepting producer writes.
 # Broker A detects the ZK timeout and leaves the ISR.
 # Broker A reconnects to ZK, rejoins cluster as follower for partition
 # Broker A truncates log to some offset Y such that Y > X. Broker A proceeds to catch up normally and becomes an ISR
 # ISRs for partition are now in an inconsistent state:
 ## Broker C has all offsets X through Y plus everything after
 ## Broker B has all offsets X through Y plus everything after
 ## Broker A has offsets up to X and after Y. Everything between X and Y *IS MISSING*
 # Within 5 minutes, controller trigger preferred replica election making Broker A the new leader for partition (this is default behavior)

All consumers after step 9 will not receive any messages for offsets between X and Y.

 

The root problem here seems to be broker A truncates to offset Y when rejoining the cluster. It should be truncating further back to offset X to prevent data loss

 



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