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From "Bryan Duxbury (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-5160) Hadoop reduce scheduler sometimes leaves machines idle
Date Tue, 03 Feb 2009 03:57:59 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-5160?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12669865#action_12669865

Bryan Duxbury commented on HADOOP-5160:

It seems like it should be easy enough to pass out reduce tasks to a machine one at a time.
Even with speculative execution on, this should improve the distribution of tasks.

> Hadoop reduce scheduler sometimes leaves machines idle
> ------------------------------------------------------
>                 Key: HADOOP-5160
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5160
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>            Reporter: Nathan Marz
> I have a MapReduce application with number of reducers equal to the number of machines
in the cluster (and with speculative execution turned off). However, Hadoop schedules multiple
reduces to run on single machines and leaves other machines idle. This causes contention and
seriously slows down the job. Hadoop should employ the simple heuristic of utilizing as many
machines as possible when scheduling reduces.

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