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From "Bikas Saha (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (MAPREDUCE-4893) MR AppMaster can do sub-optimal assignment of containers to map tasks leading to poor node locality
Date Wed, 30 Jan 2013 04:31:14 GMT

     [ https://issues.apache.org/jira/browse/MAPREDUCE-4893?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Bikas Saha updated MAPREDUCE-4893:
----------------------------------

    Attachment: MAPREDUCE-4893.3.patch

Fixed. While refactoring, I did not notice the || clause in the first if() condition that
covers this case. Attached new patch.
                
> 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, MAPREDUCE-4893.2.patch, MAPREDUCE-4893.3.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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