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https://issues.apache.org/jira/browse/FLINK-10333?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16954692#comment-16954692
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Till Rohrmann commented on FLINK-10333:
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I see the problem [~tison]. What we need for the
{{ZooKeeperHighAvailabilityServicesNG}} is to bind the {{JobGraphStore}} to the
leader session of the contender and the current {{HighAvailabilityServices}}
interface does not allow to express this relationship. That's why you need to
introduce the {{LeaderStore}} parameter, right?
So ideally, if we say that the {{JobGraphStore}} and the
{{CompletedCheckpointStore}} are bound to the leader session, then we would
only be able to instantiate them after we have obtained the leadership.
I agree that this is a bigger refactoring which I initially thought would not
be necessary to implement a new {{ZooKeeper}} based HAServices implementation.
Given that, I think you are right that we should first think about where we
wanna end up with the HAServices interfaces. Once we have agreed on this, then
your proposed intermediate step to introduce a {{LeaderStore}} parameter to
the {{getJobGraphStore}} method might be a first incremental step towards this
direction.
> 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: Runtime / Coordination
> Affects Versions: 1.5.3, 1.6.0, 1.7.0
> Reporter: Till Rohrmann
> Priority: Major
> Attachments: screenshot-1.png
>
>
> 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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