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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-4512) Add option for persistent checkpoints
Date Wed, 12 Oct 2016 15:25:20 GMT

    [ https://issues.apache.org/jira/browse/FLINK-4512?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15569028#comment-15569028
] 

ASF GitHub Bot commented on FLINK-4512:
---------------------------------------

Github user StephanEwen commented on the issue:

    https://github.com/apache/flink/pull/2608
  
    +1 to the general approach and the code
    
    Some suggestions for name polishing:
      - How about renaming `DISCARD_ON_CANCELLATION` to `DELETE_ON_CANCELLATION`? That would
sound more explicit like "cleanup" and actual file deletion.
      - Since all checkpoints are persistent (at least in HA), how about calling this `enableExternalizedCheckpoints()`
rather than `enablePersistentCheckpoints()`?
      - I would suggest to drop the method `enablePersistentCheckpoints()` without a cleanup
policy parameter. Whoever enables that feature should explicitly think about what cleanup
policy they want.
    
    For the future, can we get rid of the extra storage location for the externalized checkpoint
metadata? Simply store it as well in the checkpoint directory? That makes it simpler for users
to track and clean up checkpoints manually, if they want to retain externalized checkpoints
across cancellations and terminal failures.
      - Both the config value and the location parameter to the `enablePersistentCheckpoints()`
would be dropped.
      - That would imply that every state backend needs to be able to provide a storage location
for the checkpoint metadata
      - The memory state backend would hence not work with externalized checkpoints, unless
one sets explicitly a parameter `setExternalizedCheckpointsLocation(uri)`.`
    
    Since this is a bigger change, I would suggest a followup pull request for that. The only
change I would make to this pull request (to make transition to the followup smoother) is
to remove the path parameter from the `enablePersistentCheckpoints()` methods and always use
the configuration value (which will be replaced by the state backend's storage location).


> Add option for persistent checkpoints
> -------------------------------------
>
>                 Key: FLINK-4512
>                 URL: https://issues.apache.org/jira/browse/FLINK-4512
>             Project: Flink
>          Issue Type: Sub-task
>          Components: State Backends, Checkpointing
>            Reporter: Ufuk Celebi
>            Assignee: Ufuk Celebi
>
> Allow periodic checkpoints to be persisted by writing out their meta data. This is what
we currently do for savepoints, but in the future checkpoints and savepoints are likely to
diverge with respect to guarantees they give for updatability, etc.
> This means that the difference between persistent checkpoints and savepoints in the long
term will be that persistent checkpoints can only be restored with the same job settings (like
parallelism, etc.)
> Regular and persisted checkpoints should behave differently with respect to disposal
in *globally* terminal job states (FINISHED, CANCELLED, FAILED): regular checkpoints are cleaned
up in all of these cases whereas persistent checkpoints only on FINISHED. Maybe with the option
to customize behaviour on CANCELLED or FAILED.



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