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From "Karthik Kambatla (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-4505) Create a combiner bypass path for keys with a single value
Date Wed, 01 Aug 2012 19:08:03 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-4505?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13426827#comment-13426827
] 

Karthik Kambatla commented on MAPREDUCE-4505:
---------------------------------------------

Given the overheads involved, it might not be a bad idea to skip the combiner for more than
just a single value. The threshold for running the combiner can be number of values or a cumulative
size of the values.
                
> Create a combiner bypass path for keys with a single value
> ----------------------------------------------------------
>
>                 Key: MAPREDUCE-4505
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4505
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: performance, task
>            Reporter: Owen O'Malley
>            Assignee: Arun C Murthy
>
> It would help optimize a lot of cases where there aren't a lot of replicated keys if
the framework would bypass the deserialize/combiner/serialize step for keys that only have
a single value.

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