[jira] [Commented] (FLINK-1419) DistributedCache doesn't preserver files for subsequent operations

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-1419?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14300784#comment-14300784 ] 

ASF GitHub Bot commented on FLINK-1419:
---------------------------------------

Github user fhueske commented on the pull request:

    https://github.com/apache/flink/pull/339#issuecomment-72390974
  
    +1, will merge. Thanks @zentol & @tillrohrmann!


> DistributedCache doesn't preserver files for subsequent operations
> ------------------------------------------------------------------
>
>                 Key: FLINK-1419
>                 URL: https://issues.apache.org/jira/browse/FLINK-1419
>             Project: Flink
>          Issue Type: Bug
>    Affects Versions: 0.8, 0.9
>            Reporter: Chesnay Schepler
>            Assignee: Chesnay Schepler
>
> When subsequent operations want to access the same files in the DC it frequently happens that the files are not created for the following operation.
> This is fairly odd, since the DC is supposed to either a) preserve files when another operation kicks in within a certain time window, or b) just recreate the deleted files. Both things don't happen.
> Increasing the time window had no effect.
> I'd like to use this issue as a starting point for a more general discussion about the DistributedCache. 
> Currently:
> 1. all files reside in a common job-specific directory
> 2. are deleted during the job.
>  
> One thing that was brought up about Trait 1 is that it basically forbids modification of the files, concurrent access and all. Personally I'm not sure if this a problem. Changing it to a task-specific place solved the issue though.
> I'm more concerned about Trait #2. Besides the mentioned issue, the deletion is realized with the scheduler, which adds a lot of complexity to the current code. (It really is a pain to work on...) 
> If we moved the deletion to the end of the job it could be done as a clean-up step in the TaskManager, With this we could reduce the DC to a cacheFile(String source) method, the delete method in the TM, and throw out everything else.
> Also, the current implementation implies that big files may be copied multiple times. This may be undesired, depending on how big the files are.



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