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From "Hudson (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-7151) Document need for stable hashCode() in WritableComparable
Date Fri, 25 Feb 2011 06:12:38 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7151?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12999227#comment-12999227
] 

Hudson commented on HADOOP-7151:
--------------------------------

Integrated in Hadoop-Common-trunk-Commit #511 (See [https://hudson.apache.org/hudson/job/Hadoop-Common-trunk-Commit/511/])
    HADOOP-7151. Document need for stable hashCode() in WritableComparable. Contributed by
Dmitriy V. Ryaboy.


> Document need for stable hashCode() in WritableComparable
> ---------------------------------------------------------
>
>                 Key: HADOOP-7151
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7151
>             Project: Hadoop Common
>          Issue Type: Bug
>            Reporter: Dmitriy V. Ryaboy
>            Assignee: Dmitriy V. Ryaboy
>            Priority: Minor
>             Fix For: 0.23.0
>
>         Attachments: HADOOP-7151.patch, HADOOP-7151.patch
>
>
> When a Writable is used as a key, HashPartitioner implicitly assumes that hashCode()
will return the same value across different instances of the JVM. This is not a guaranteed
behavior in Java, and Object's default hashCode() does not in fact do this, which can lead
to subtle bugs. This requirement should be explicitly called out.
> In addition the sample MyWritable in the javadoc for WritableComparable does not implement
hashCode() and thus has a bug. That should be fixed.

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