[jira] Commented: (HADOOP-3651) When assigning tasks to trackers, the job tracker should try to balance the number of tasks among the available trackers

["Amar Kamat (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-3651?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12609594#action_12609594 ] 

Amar Kamat commented on HADOOP-3651:
------------------------------------

Runping,
I tried to reproduce this by running a job with N trackers and N reducers (N = 8,28) and all the reducers were on different host. Is there any other way/setting to reproduce this?

> When assigning tasks to trackers, the job tracker should try to balance the number of tasks among the available trackers
> ------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-3651
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3651
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: mapred
>    Affects Versions: 0.17.0
>            Reporter: Runping Qi
>
> I encounter a number of situations like this:
> A job tracker has 200 task trackers, each with 2 mapper slots and reducer slots.
> When a job with 200 or fewer reducers was submitted to the job tracker,
> one normally each task tracker will run one reducer.
> Unfortunately, it seems that only  about 1/3 of trackers have one reducer, and 1/3 trackers don't have reducer, and 1/3 have 2 reducers!

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