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Date: Wed, 30 Dec 2009 21:10:29 +0000 (UTC)
From: "Tom White (JIRA)" <jira@apache.org>
To: mapreduce-issues@hadoop.apache.org
Subject: [jira] Commented: (MAPREDUCE-1287) HashPartitioner calls hashCode()
 when there is only 1 reducer
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    [ https://issues.apache.org/jira/browse/MAPREDUCE-1287?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12795447#action_12795447 ] 

Tom White commented on MAPREDUCE-1287:
--------------------------------------

Any reason that the old partitioner uses {{1 - numPartitions}} and the new one uses {{partitions - 1}}? It shouldn't make any difference since the partitioner is not actually used in the zero partition case, but it would be good to make the code consistent.

> Clearly, any application that depends on the partitioner for correctness can be rewritten, but is it worth calling out?

I think so - put a comment in the release notes.

> HashPartitioner calls hashCode() when there is only 1 reducer
> -------------------------------------------------------------
>
>                 Key: MAPREDUCE-1287
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1287
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>    Affects Versions: 0.22.0
>            Reporter: Ed Mazur
>            Assignee: Ed Mazur
>            Priority: Minor
>             Fix For: 0.22.0
>
>         Attachments: M1287-4.patch, MAPREDUCE-1287.2.patch, MAPREDUCE-1287.3.patch, MAPREDUCE-1287.patch
>
>
> HashPartitioner could be optimized to not call the key's hashCode() if there is only 1 reducer.

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