Document need for stable hashCode() in WritableComparable
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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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