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From StephanEwen <...@git.apache.org>
Subject [GitHub] flink issue #2608: [FLINK-4512] [FLIP-10] Add option to persist periodic che...
Date Wed, 12 Oct 2016 15:24:58 GMT
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).


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