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https://issues.apache.org/jira/browse/FLINK-2354?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14940974#comment-14940974
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ASF GitHub Bot commented on FLINK-2354:
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Github user uce commented on the pull request:
https://github.com/apache/flink/pull/1153#issuecomment-144979369
While working on FLINK-2804 I've noticed an issue: the user jars are only
uploaded to the leading job manager at submission time and then are not
available to the other job managers on recovery. A simple solution is to make
the user jars available in the file state backend as well.
> Recover running jobs on JobManager failure
> ------------------------------------------
>
> Key: FLINK-2354
> URL: https://issues.apache.org/jira/browse/FLINK-2354
> Project: Flink
> Issue Type: Sub-task
> Components: JobManager
> Affects Versions: master
> Reporter: Ufuk Celebi
> Assignee: Ufuk Celebi
> Fix For: 0.10
>
>
> tl;dr Persist JobGraphs in state backend and coordinate reference to state
> handle via ZooKeeper.
> Problem: When running multiple JobManagers in high availability mode, the
> leading job manager looses all running jobs when it fails. After a new
> leading job manager is elected, it is not possible to recover any previously
> running jobs.
> Solution: The leading job manager, which receives the job graph writes 1) the
> job graph to a state backend, and 2) a reference to the respective state
> handle to ZooKeeper. In general, job graphs can become large (multiple MBs,
> because they include closures etc.). ZooKeeper is not designed for data of
> this size. The level of indirection via the reference to the state backend
> keeps the data in ZooKeeper small.
> Proposed ZooKeeper layout:
> /flink (default)
> +- currentJobs
> +- job id i
> +- state handle reference of job graph i
> The 'currentJobs' node needs to be persistent to allow recovery of jobs
> between job managers. The currentJobs node needs to satisfy the following
> invariant: There is a reference to a job graph with id i IFF the respective
> job graph needs to be recovered by a newly elected job manager leader.
> With this in place, jobs will be recovered from their initial state (as if
> resubmitted). The next step is to backup the runtime state handles of
> checkpoints in a similar manner.
> ---
> This work will be based on [~trohrm...@apache.org]'s implementation of
> FLINK-2291. The leader election service notifies the job manager about
> granted/revoked leadership. This notification happens via Akka and thus
> serially *per* job manager, but results in eventually consistent state
> between job managers. For some snapshots of time it is possible to have a new
> leader granted leadership, before the old one has been revoked its leadership.
> [~trohrm...@apache.org], can you confirm that leadership does not guarantee
> mutually exclusive access to the shared 'currentJobs' state?
> For example, the following can happen:
> - JM 1 is leader, JM 2 is standby
> - JOB i is running (and hence /flink/currentJobs/i exists)
> - ZK notifies leader election service (LES) of JM 1 and JM 2
> - LES 2 immediately notifies JM 2 about granted leadership, but LES 1
> notification revoking leadership takes longer
> - JOB i finishes (TMs don't notice leadership change yet) and JM 1 receives
> final JobStatusChange
> - JM 2 resubmits the job /flink/currentJobs/i
> - JM 1 removes /flink/currentJobs/i, because it is now finished
> => inconsistent state (wrt the specified invariant above)
> If it is indeed a problem, we can circumvent this with a Curator recipe for
> [shared locks|http://curator.apache.org/curator-recipes/shared-lock.html] to
> coordinate the access to currentJobs. The lock needs to be acquired on
> leadership.
> ---
> Minimum required tests:
> - Unit tests for job graph serialization and writing to state backend and
> ZooKeeper with expected nodes
> - Unit tests for job submission to job manager in leader/non-leader state
> - Unit tests for leadership granting/revoking and job submission/restarting
> interleavings
> - Process failure integration tests with single and multiple running jobs
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