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https://issues.apache.org/jira/browse/MAPREDUCE-1892?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13016899#comment-13016899
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Hudson commented on MAPREDUCE-1892:
-----------------------------------
Integrated in Hadoop-Mapreduce-trunk #643 (See
[https://hudson.apache.org/hudson/job/Hadoop-Mapreduce-trunk/643/])
> RaidNode can allow layered policies more efficiently
> ----------------------------------------------------
>
> Key: MAPREDUCE-1892
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-1892
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Components: contrib/raid
> Reporter: Ramkumar Vadali
> Assignee: Ramkumar Vadali
> Fix For: 0.22.0
>
> Attachments: MAPREDUCE-1892.patch, MAPREDUCE-1892.patch
>
>
> The RaidNode policy file can have layered policies that can cover a file more
> than once. To avoid processing a file multiple times (for RAIDing), RaidNode
> maintains a list of processed files that is used to avoid duplicate
> processing attempts.
> This is problematic in that a large number of processed files could cause the
> RaidNode to run out of memory.
> This task proposes a better method of detecting processed files. The method
> is based on the observation that a more selective policy will have a better
> match with a file name than a less selective one. Specifically, the more
> selective policy will have a longer common prefix with the file name.
> So to detect if a file has already been processed, the RaidNode only needs to
> maintain a list of processed policies and compare the lengths of the common
> prefixes. If the file has a longer common prefix with one of the processed
> policies than with the current policy, it can be assumed to be processed
> already.
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