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Date: Tue, 11 May 2010 17:09:43 -0400 (EDT)
From: "Scott Chen (JIRA)" <jira@apache.org>
To: mapreduce-issues@hadoop.apache.org
Subject: [jira] Commented: (MAPREDUCE-1764) FairScheduler locality delay may
 put heavy pressure on Jobtracker
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    [ https://issues.apache.org/jira/browse/MAPREDUCE-1764?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12866336#action_12866336 ] 

Scott Chen commented on MAPREDUCE-1764:
---------------------------------------

One option is to cache the searched result for each TT. So next time we directly skip the TT without the allowed locality level.
What do you think?

> FairScheduler locality delay may put heavy pressure on Jobtracker
> -----------------------------------------------------------------
>
>                 Key: MAPREDUCE-1764
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1764
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>    Affects Versions: 0.22.0
>            Reporter: Scott Chen
>            Assignee: Dmytro Molkov
>             Fix For: 0.22.0
>
>
> FairScheduler locality delay feature holds the scheduling of jobs until it gets good locality.
> This greatly improves the locality of the tasks. Reduce the cost of traffic.
> We have observed the following problem on FairScheduler locality delay:
> We have some machines have older data and some newly added machines do not have important data.
> When these machines send heartbeat, JT scans tasks to find jobs has the right locality.
> Often time, these machines will scan all of the tasks of all the jobs and do not get any tasks.
> Scanning all the tasks on the JT is very costly. This makes JT very slow.
> And these machines often time do not get scheduled. This hurts the cluster utilization.
> Any ideas?

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