[jira] [Created] (MAPREDUCE-7282) MR v2 commit algorithm is dangerous, should be deprecated and not the default

["Steve Loughran (Jira)" <ji...@apache.org>]

Steve Loughran created MAPREDUCE-7282:
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             Summary: MR v2 commit algorithm is dangerous, should be deprecated and not the default
                 Key: MAPREDUCE-7282
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-7282
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: mrv2
    Affects Versions: 3.1.3, 3.2.1, 3.3.0, 3.3.1
            Reporter: Steve Loughran


The v2 MR commit algorithm moves files from the task attempt dir into the dest dir on task commit -one by one

It is therefore not atomic

# if a task commit fails partway through and another task attempt commits -unless exactly the same filenames are used, output of the first attempt may be included in the final result
# if a worker partitions partway through task commit, and then continues after another attempt has committed, it may partially overwrite the output -even when the filenames are the same

Both MR and spark assume that task commits are atomic. Either they need to consider that this is not the case, we add a way to probe for a committer supporting atomic task commit, and the engines both add handling for task commit failures (probably fail job)

Better: we remove this as the default, maybe also warn when it is being used




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