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https://issues.apache.org/jira/browse/MAPREDUCE-1288?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12892971#action_12892971
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Owen O'Malley commented on MAPREDUCE-1288:
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{quote}
(2) introduce the concept of group sharing of distributed cache files so as to
avoid repetitive downloads for group shared files also. This may be a complex
solution after all.
{quote}
This would be quite complex to get right. In particular, it is difficult to
determine which group should have access. If we want to improve it, I'd suggest
that we use hardlinks to give each user access to a single copy of the file..
Of course you need to ensure that they do in fact have read access to the
original file. *smile*
> 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: distributed-cache, security, tasktracker
> Affects Versions: 0.21.0
> Reporter: Devaraj Das
> Priority: Critical
> Attachments: MR-1288-bp20-1.patch, MR-1288-bp20-2.patch,
> MR-1288-bp20-3.patch
>
>
> 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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