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https://issues.apache.org/jira/browse/MAPREDUCE-1764?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12867424#action_12867424
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Joydeep Sen Sarma commented on MAPREDUCE-1764:
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it seems better to find out why the index is not helping (assuming it's
actually being used) rather than adding another cache on top ..
> 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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