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Posted to mapreduce-issues@hadoop.apache.org by "Radim Kolar (JIRA)" <ji...@apache.org> on 2012/12/04 17:17:58 UTC

[jira] [Updated] (MAPREDUCE-4827) Increase hash quality of HashPartitioner

     [ https://issues.apache.org/jira/browse/MAPREDUCE-4827?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Radim Kolar updated MAPREDUCE-4827:
-----------------------------------

    Status: Patch Available  (was: Open)
    
> Increase hash quality of HashPartitioner
> ----------------------------------------
>
>                 Key: MAPREDUCE-4827
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4827
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>            Reporter: Radim Kolar
>         Attachments: betterhash1.txt
>
>
> hash partitioner is using object.hashCode() for splitting keys into partitions. This results in bad distributions because hashCode() quality is poor. 
> These hashCode() functions are sometimes written by hand (very poor quality) and sometimes generated from by commons lang code (poor quality). Applying some transformation on top of hashCode() provides better distribution.

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