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

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

     [ https://issues.apache.org/jira/browse/FLINK-10333?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

TisonKun updated FLINK-10333:
-----------------------------
    Comment: was deleted

(was: Agree with [~xiaogang.shi] that our leader elections is not that perfect. The main issue here is that we check the leadership and do the real action non-atomically.

Sounds like implementation [~xiaogang.shi] suggested and that [~StephanEwen] suggested worked. [~xiaogang.shi]'s suggestion looks good to me but it causes a bit many works to do. [~StephanEwen]'s suggestion is more simple but I don't find a settable {{id}}(i.e., the payload) in curator 2.12.0 and we need to add leader ID to the payload after leadership granted.)

> 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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