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From "Dmitriy V. Ryaboy (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-7151) Document need for stable hashCode() in WritableComparable
Date Sat, 19 Feb 2011 04:51:38 GMT
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
            Priority: Minor


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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