[jira] [Created] (FLINK-6612) ZooKeeperStateHandleStore does not guard against concurrent delete operations

["Till Rohrmann (JIRA)" <ji...@apache.org>]

Till Rohrmann created FLINK-6612:
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             Summary: ZooKeeperStateHandleStore does not guard against concurrent delete operations
                 Key: FLINK-6612
                 URL: https://issues.apache.org/jira/browse/FLINK-6612
             Project: Flink
          Issue Type: Bug
          Components: Distributed Coordination, State Backends, Checkpointing
    Affects Versions: 1.3.0, 1.4.0
            Reporter: Till Rohrmann
            Assignee: Till Rohrmann
            Priority: Critical
             Fix For: 1.3.0, 1.4.0


The {{ZooKeeperStateHandleStore}} does not guard against concurrent delete operations which could happen in case of a lost leadership and a new leadership grant. The problem is that checkpoint nodes can get deleted even after they have been recovered by another {{ZooKeeperCompletedCheckpointStore}}. This corrupts the recovered checkpoint and thwarts future recoveries.

I propose to add reference counting to the {{ZooKeeperStateHandleStore}}. That way, we can monitor how many concurrent processes have a hold on a given checkpoint node. Only if the reference count reaches {{0}}, we are allowed to delete the checkpoint node and dispose the checkpoint data.

Stephan proposed to use ephemeral child nodes to track the reference count of a checkpoint node. That way we are sure that locks on the a checkpoint node are released in case of {{JobManager}} failures.



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