Erik Krogen commented on MAPREDUCE-6870:

Given its rarity and that the worst case scenario is {{(expected execution 
time) + (single mapper execution time)}} I would consider it not a severe 
issue, which leans me towards compatibility. However the current behavior is 
pretty confusing for an average user, so, tough call.

We would like to backport this to older release lines, in which case we 
definitely need to maintain compatibility and thus have default = false. As for 
trunk I am on the fence.

> Add configuration for MR job to finish when all reducers are complete (even 
> with unfinished mappers)
> ----------------------------------------------------------------------------------------------------
>                 Key: MAPREDUCE-6870
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-6870
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>    Affects Versions: 2.6.1
>            Reporter: Zhe Zhang
>            Assignee: Peter Bacsko
>             Fix For: 3.0.0-beta1
>         Attachments: MAPREDUCE-6870-001.patch, MAPREDUCE-6870-002.patch, 
> MAPREDUCE-6870-003.patch, MAPREDUCE-6870-004.patch, MAPREDUCE-6870-005.patch, 
> MAPREDUCE-6870-006.patch, MAPREDUCE-6870-007.patch
> Even with MAPREDUCE-5817, there could still be cases where mappers get 
> scheduled before all reducers are complete, but those mappers run for long 
> time, even after all reducers are complete. This could hurt the performance 
> of large MR jobs.
> In some cases, mappers don't have any materialize-able outcome other than 
> providing intermediate data to reducers. In that case, the job owner should 
> have the config option to finish the job once all reducers are complete.

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