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https://issues.apache.org/jira/browse/FLINK-10333?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16701821#comment-16701821
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Xiaogang Shi commented on FLINK-10333:
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hi [~StephanEwen], I think the key point to achieve atomicity is the usage of
Zookeeper transactions, ensuring that every modification to ZooKeeper only
takes effect when the corresponding election node exists. As far as i know,
ZooKeeper transactions only support the checks on the existence of given paths,
and do not support the checks on the payload. Hence i think adding the leader
ID as payload to the ephemeral node does not help in achieving atomicity.
What do you think?
> 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: 1.5.3, 1.6.0, 1.7.0
> Reporter: Till Rohrmann
> Priority: Major
> Fix For: 1.8.0
>
>
> 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
> * Shadowing of ZooKeeper specific exceptions in {{ZooKeeperStateHandleStore}}
> which were expected to be caught in {{ZooKeeperSubmittedJobGraphStore}}
> * Getting rid of the {{SubmittedJobGraphListener}} would be helpful
> 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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