[SPARK-2148] Document custom class as key needing equals() AND hashcode()

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.0.0
• Fix Version/s: 1.0.1, 1.1.0
• Component/s: Documentation
• Assignee: Andrew Ash
• Reporter: Andrew Ash
• Created: 15/Jun/14 17:01
• Updated: 16/Jun/14 06:33
• Resolved: 16/Jun/14 06:33

Description

Several support requests on user@ have been tracked down to using a custom class as the key in a groupByKey() or reduceByKey() that has a custom equals() method but not the corresponding custom hashCode() method.

Let's add a note in the documentation that custom keys need both equals() and hashCode() overridden, never just equals()

The right place for this addition might be as a sub-section or note in http://spark.apache.org/docs/latest/programming-guide.html#working-with-key-value-pairs

It should probably include a link to http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#hashCode()