[HADOOP-7151] Document need for stable hashCode() in WritableComparable

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 0.23.0
• Hadoop Flags: Reviewed
• Assignee: Dmitriy V. Ryaboy
• Reporter: Dmitriy V. Ryaboy
• Created: 19/Feb/11 04:51
• Updated: 15/Nov/11 00:50
• Resolved: 24/Feb/11 18:06

Description

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.