[HADOOP-9124] SortedMapWritable violates contract of Map interface for equals() and hashCode()

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 1.1.1, 2.0.2-alpha
• Fix Version/s: 1.2.0, 2.0.3-alpha, 0.23.7
• Component/s: io
• Target Version/s: 1.2.0
• Hadoop Flags: Reviewed
• Assignee: Surenkumar Nihalani
• Reporter: Patrick D. Hunt
• Created: 08/Dec/12 00:55
• Updated: 15/Feb/13 13:12
• Resolved: 07/Feb/13 10:43

Description

This issue is similar to HADOOP-7153. It was found when using MRUnit - see MRUNIT-158, specifically https://issues.apache.org/jira/browse/MRUNIT-158?focusedCommentId=13501985&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13501985

–
o.a.h.io.SortedMapWritable implements the java.util.Map interface, however it does not define an implementation of the equals() or hashCode() methods; instead the default implementations in java.lang.Object are used.

This violates the contract of the Map interface which defines different behaviour for equals() and hashCode() than Object does. More information here: http://download.oracle.com/javase/6/docs/api/java/util/Map.html#equals(java.lang.Object)

The practical consequence is that SortedMapWritables containing equal entries cannot be compared properly. We were bitten by this when trying to write an MRUnit test for a Mapper that outputs MapWritables; the MRUnit driver cannot test the equality of the expected and actual MapWritable objects.

Issue Links

• blocks: HADOOP-9154 SortedMapWritable#putAll() doesn't add key/value classes to the map
• is related to: HADOOP-7153 MapWritable violates contract of Map interface for equals() and hashCode()
• relates to: MRUNIT-158 withOutput doesn't generate useful information with MapWritable on error