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https://issues.apache.org/jira/browse/HBASE-10017?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13837964#comment-13837964
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Roman Nikitchenko commented on HBASE-10017:
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It looks like this partitioner defect also can cause some data loss in 
incremental HFile loading based on HFileOutputFormat configured MR job. This is 
because they use such partitioner to partition records between HFile and 
records might get to wrong region.
Too much effect from too easy to fix issue.



> HRegionPartitioner, rows directed to last partition are wrongly mapped.
> -----------------------------------------------------------------------
>
>                 Key: HBASE-10017
>                 URL: https://issues.apache.org/jira/browse/HBASE-10017
>             Project: HBase
>          Issue Type: Bug
>          Components: mapreduce
>    Affects Versions: 0.94.6
>            Reporter: Roman Nikitchenko
>            Priority: Critical
>         Attachments: HBASE-10017-r1544633.patch, HBASE-10017-r1544633.patch, 
> patchSiteOutput.txt
>
>
> Inside HRegionPartitioner class there is getPartition() method which should 
> map first numPartitions regions to appropriate partitions 1:1. But based on 
> condition last region is hashed which could lead to last reducer not having 
> any data. This is considered serious issue.
> I reproduced this only starting from 16 regions per table. Original defect 
> was found in 0.94.6 but at least today's trunk and 0.91 branch head have the 
> same HRegionPartitioner code in this part which means the same issue.



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