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From "Devaraj Das (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-1288) DistributedCache localizes only once per cache URI
Date Fri, 11 Dec 2009 07:19:18 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1288?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12789153#action_12789153
] 

Devaraj Das commented on MAPREDUCE-1288:
----------------------------------------

All I am saying is that irrespective of the file being public or not, in the current codebase,
we localize the file exactly once per TaskTracker. On a given tasktracker, users cannot share
the same hdfs file as a distributed cache file.. 
What I thought earlier was that the same file would be localized twice in such a case (in
their respective private directories).

> DistributedCache localizes only once per cache URI
> --------------------------------------------------
>
>                 Key: MAPREDUCE-1288
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1288
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: security, tasktracker
>    Affects Versions: 0.21.0
>            Reporter: Devaraj Das
>            Priority: Blocker
>             Fix For: 0.21.0
>
>
> As part of the file localization the distributed cache localizer creates a copy of the
file in the corresponding user's private directory. The localization in DistributedCache assumes
the key as the URI of the cachefile and if it already exists in the map, the localization
is not done again. This means that another user cannot access the same distributed cache file.
We should change the key to include the username so that localization is done for every user.

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