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From "Paul Baclace (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-9) mapred.local.dir temp dir. space allocation limited by smallest area
Date Sat, 06 Nov 2010 05:28:43 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-9?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12928934#action_12928934
] 

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

Ari,

This issue was originally NUTCH-181 before Hadoop was split off.  I wrote a patch Dec. 29
2005 and used it at archive.org Jan-Feb 2006.  Looking at my old notes, I created this issue
on Jan. 11 2006, and prepared the patch on Feb. 28 2006, but it was either lost in a Jira
transition or the attachment somehow failed.  

When I looked at your patch yesterday, it was similar enough to what I remembered (5 years
ago) that I thought it must be a revision of the patch I did.  Today I found my source and
2005-2006 work notes and it is clear that you implemented the change without seeing mine.

Thanks for doing it in same "roulette-y" spirit of my lost 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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