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From "Scott Chen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-1764) FairScheduler locality delay may put heavy pressure on Jobtracker
Date Thu, 13 May 2010 22:57:45 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1764?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12867300#action_12867300

Scott Chen commented on MAPREDUCE-1764:


Matei and I had some discussion and we have also looked the code.
In JobInProgress, there is such a HashMap of node->[tasks] and rack->[tasks] exists.
It is not clear to me why this is so slow.

I agree with your point that we should not leave the slots idle especially in the case that
cluster is full of jobs.

> 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
> 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
> 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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