[jira] [Created] (FLINK-10333) Rethink ZooKeeper based stores (SubmittedJobGraph, MesosWorker, CompletedCheckpoints)

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

Till Rohrmann created FLINK-10333:
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             Summary: Rethink ZooKeeper based stores (SubmittedJobGraph, MesosWorker, CompletedCheckpoints)
                 Key: FLINK-10333
                 URL: https://issues.apache.org/jira/browse/FLINK-10333
             Project: Flink
          Issue Type: Bug
          Components: Distributed Coordination
    Affects Versions: 1.6.0, 1.5.3, 1.7.0
            Reporter: Till Rohrmann
             Fix For: 1.7.0


While going over the ZooKeeper based stores ({{ZooKeeperSubmittedJobGraphStore}}, {{ZooKeeperMesosWorkerStore}}, {{ZooKeeperCompletedCheckpointStore}}) and the underlying {{ZooKeeperStateHandleStore}} I noticed several inconsistencies which were introduced with past incremental changes.

* Depending whether {{ZooKeeperStateHandleStore#getAllSortedByNameAndLock}} or {{ZooKeeperStateHandleStore#getAllAndLock}} is called, deserialization problems will either lead to removing the Znode or not
* {{ZooKeeperStateHandleStore}} leaves inconsistent state in case of exceptions (e.g. {{#getAllAndLock}} won't release the acquired locks in case of a failure)
* {{ZooKeeperStateHandleStore}} has too many responsibilities. It would be better to move {{RetrievableStateStorageHelper}} out of it for a better separation of concerns
* {{ZooKeeperSubmittedJobGraphStore}} overwrites a stored {{JobGraph}} even if it is locked. This should not happen since it could leave another system in an inconsistent state (imagine a changed {{JobGraph}} which restores from an old checkpoint)
* Redundant but also somewhat inconsistent put logic in the different stores

These problems made me think how reliable these components actually work. Since these components are very important, I propose to refactor them.



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