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https://issues.apache.org/jira/browse/HADOOP-3651?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12608751#action_12608751
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Devaraj Das commented on HADOOP-3651:
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Runping, can you tell us whether there was more than one job simulataneously
active in the cluster?
I don't think that the load factor calculation is affecting this. If you take a
cluster with 200 tasktrackers and a job with 200 reducers (and that is the only
job in the cluster), then it is guaranteed (as per the load factor code) that
no more than one reduce task will be assigned to a tasktracker. Of course, if
you have things like lost trackers then some tasktrackers will run more than
one.
> 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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