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https://issues.apache.org/jira/browse/HADOOP-3019?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12578915#action_12578915
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Doug Cutting commented on HADOOP-3019:
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> Should this be a part of examples like sort?

I guess  it could live with the examples, but I was thinking that this would be 
more like mapred/lib.  The sampler should be generic enough that folks won't 
have to modify it to find it useful: it should work for different key/value 
types and for sequencefile and text data.

> want input sampler & sorted partitioner
> ---------------------------------------
>
>                 Key: HADOOP-3019
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3019
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: mapred
>            Reporter: Doug Cutting
>
> The input sampler should generate a small, random sample of the input, saved 
> to a file.
> The partitioner should read the sample file and partition keys into 
> relatively even-sized key-ranges, where the partition numbers correspond to 
> key order.
> Note that when the sampler is used for partitioning, the number of samples 
> required is proportional to the number of reduce partitions.  10x the 
> intended reducer count should give good results.

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