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https://issues.apache.org/jira/browse/HIVE-7074?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14025996#comment-14025996
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Gunther Hagleitner commented on HIVE-7074:
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I believe that's unnecessary given HIVE-7121. Once we do a decent job of
hashing the keys the prime number reducer requirement goes away.
> The reducer parallelism should be a prime number for better stride protection
> -----------------------------------------------------------------------------
>
> Key: HIVE-7074
> URL: https://issues.apache.org/jira/browse/HIVE-7074
> Project: Hive
> Issue Type: Improvement
> Components: Statistics
> Reporter: Gopal V
> Assignee: Gopal V
> Attachments: HIVE-7074.1.patch
>
>
> The current hive reducer parallelism results in stride issues with key
> distribution.
> a JOIN generating even numbers will get strided onto only some of the
> reducers.
> The probability of distribution skew is controlled by the number of common
> factors shared by the hashcode of the key and the number of buckets.
> Using a prime number within the reducer estimation will cut that probability
> down by a significant amount.
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