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From "Alan Gates (JIRA)" <j...@apache.org>
Subject [jira] Assigned: (PIG-871) Improve distribution of keys in reduce phase
Date Tue, 21 Sep 2010 20:30:34 GMT

     [ https://issues.apache.org/jira/browse/PIG-871?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Alan Gates reassigned PIG-871:

    Assignee: Thejas M Nair

> Improve distribution of keys in reduce phase
> --------------------------------------------
>                 Key: PIG-871
>                 URL: https://issues.apache.org/jira/browse/PIG-871
>             Project: Pig
>          Issue Type: Improvement
>    Affects Versions: 0.3.0
>            Reporter: Ankur
>            Assignee: Thejas M Nair
> The default hashing scheme used to distribute keys in reduce phase sometimes results
in an uneven distribution of keys resulting in 5 - 10 % of reducers being overloaded with
data. This bottleneck makes the PIG jobs really slow and gives users a bad impression.
> While there is no bullet proof solution to the problem in general, the hashing can certainly
be improved for better distribution. The proposal here is to evaluate and incorporate other
hashing schemes that give high avalanche and more even distribution. We can start by evaluating
MurmurHash which is Apache 2.0 licensed and freely available here - http://www.getopt.org/murmur/MurmurHash.java

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