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From "Miklos Szegedi (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-5686) DefaultContainerExecutor random working dir algorigthm skews results
Date Fri, 21 Oct 2016 00:48:58 GMT

    [ https://issues.apache.org/jira/browse/YARN-5686?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15593533#comment-15593533
] 

Miklos Szegedi commented on YARN-5686:
--------------------------------------

+1 (non-binding) It looks good to me. Thank you, [~vrushalic]!

> DefaultContainerExecutor random working dir algorigthm skews results
> --------------------------------------------------------------------
>
>                 Key: YARN-5686
>                 URL: https://issues.apache.org/jira/browse/YARN-5686
>             Project: Hadoop YARN
>          Issue Type: Bug
>            Reporter: Miklos Szegedi
>            Assignee: Vrushali C
>            Priority: Minor
>         Attachments: YARN-5686.001.patch, YARN-5686.002.patch
>
>
> {code}
> long randomPosition = RandomUtils.nextLong() % totalAvailable;
>     ...
>     while (randomPosition > availableOnDisk[dir]) {
>       randomPosition -= availableOnDisk[dir++];
>     }
> {code}
> The code above selects a disk based on the random number weighted by the free space on
each disk respectively. For example, if I have two disks with 100 bytes each, totalAvailable
is 200. The value of randomPosition will be 0..199. 0..99 should select the first disk, 100..199
should select the second disk inclusively. Random number 100 should select the second disk
to be fair but this is not the case right now.
> We need to use 
> {code}
> while (randomPosition >= availableOnDisk[dir])
> {code}
> instead of
> {code}
> while (randomPosition > availableOnDisk[dir])
> {code}



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