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From "ASF GitHub Bot (Jira)" <j...@apache.org>
Subject [jira] [Work logged] (MAPREDUCE-7282) MR v2 commit algorithm should be deprecated and not the default
Date Thu, 10 Jun 2021 20:59:01 GMT

     [ https://issues.apache.org/jira/browse/MAPREDUCE-7282?focusedWorklogId=609929&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-609929
]

ASF GitHub Bot logged work on MAPREDUCE-7282:
---------------------------------------------

                Author: ASF GitHub Bot
            Created on: 10/Jun/21 20:58
            Start Date: 10/Jun/21 20:58
    Worklog Time Spent: 10m 
      Work Description: steveloughran commented on pull request #2349:
URL: https://github.com/apache/hadoop/pull/2349#issuecomment-859061589


   Once the manifest committer #2971 is in, the abfs and gcs stores will get something faster
than v1 but with its task failure semantics
   * all treewalking for task attempt listing will be in task commit
   * no dir renames in task commit, just saving of the manifest
   * job commit: parallel load of manifests, merge of list of directories to create, parallel
set of mkdirs and then the parallelized renames. 
   
   In this world, we can just leave people using v1/v2 alone, and for (spark) jobs in azure
and google cloud say "use the manifest committer". 
   Which means I can just close this as a wontfix.


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Issue Time Tracking
-------------------

            Worklog Id:     (was: 609929)
    Remaining Estimate: 0h
            Time Spent: 10m

> MR v2 commit algorithm 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: 3.3.0, 3.2.1, 3.1.3, 3.3.1
>            Reporter: Steve Loughran
>            Priority: Major
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> 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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