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https://issues.apache.org/jira/browse/MAPREDUCE-4893?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13536590#comment-13536590
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Bikas Saha commented on MAPREDUCE-4893:
---------------------------------------
Test passes when run locally. Trying again.
> MR AppMaster can do sub-optimal assignment of containers to map tasks leading
> to poor node locality
> ---------------------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-4893
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4893
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Reporter: Bikas Saha
> Assignee: Bikas Saha
> Fix For: 3.0.0
>
> Attachments: MAPREDUCE-4893.1.patch
>
>
> Say the MR AppMaster asks the RM for 3 containers on nodes n1, n2 and n3.
> There are 10 node n1-n10 in the same rack. The RM can give it allocated
> containers in the list order n5, n2, n1. The way AM map->container assignment
> happens, the AM will try to assign node local maps to n5, failing which it
> will assign rack local maps to n5. These rack local maps could be node local
> on n2 and n1 and would have been assigned to containers on n1 and n2 if the
> AM had not made an early rack local match for them on n5. This can lead to
> poor locality.
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