[HADOOP-7021] MapWritable NullPointerException

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 0.20.1, 0.21.0
• Component/s: io
• Labels: BB2015-05-RFC

Environment

Hadoop 0.20.1, Centos

• Release Note: Found a NullPointerException with MapWritable. The root cause is the counter newClasses in AbstractMapWritable is allowed to get out of sync with the id to class mapping tables when addToMap(Class) is called.
• Assignee: John Lee
• Reporter: John Lee
• Created: 05/Nov/10 14:02
• Updated: 28/May/15 18:21

Description

We have encountered a NullPointerException when we use MapWritable with custom Writable objects.

The root cause is the counter newClasses in AbstractMapWritable is allowed to get out of sync with the id to class mapping tables when addToMap(Class) is called. We have a patch to AbstractMapWritable.addToMap(Class) that handles the case when newClasses gets out of sync with the id to class mapping tables and adds a serialization optimization to minimize the number of class names to write out per MapWritable object.