[jira] Commented: (HADOOP-9) mapred.local.dir temp dir. space allocation limited by smallest area

["Paul Baclace (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-9?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12928463#action_12928463 ] 

Paul Baclace commented on HADOOP-9:
-----------------------------------

You're welcome, Owen!   (I wrote the roulette selection patch.)


> mapred.local.dir  temp dir. space allocation limited by smallest area
> ---------------------------------------------------------------------
>
>                 Key: HADOOP-9
>                 URL: https://issues.apache.org/jira/browse/HADOOP-9
>             Project: Hadoop Common
>          Issue Type: Bug
>         Environment: all
>            Reporter: Paul Baclace
>            Assignee: Ari Rabkin
>            Priority: Minor
>             Fix For: 0.19.0
>
>         Attachments: hadoop9.patch
>
>
> When mapred.local.dir is used to specify multiple  temp dir. areas, space allocation limited by smallest area because the temp dir. selection algorithm is "round robin starting from a randomish point".   When round robin is used with approximately constant sized chunks, the smallest area runs out of space first, and this is a fatal error. 
> Workaround: only list local fs dirs in mapred.local.dir with similarly-sized available areas.
> I wrote a patch to JobConf (currenly being tested) which uses df to check available space (once a minute or less often) and then uses an efficient roulette selection to do allocation weighted by magnitude of available space. 

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