[MAPREDUCE-969] NullPointerException during reduce freezes job

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Duplicate
• Affects Version/s: 0.20.2
• Component/s: jobtracker, task, tasktracker
• Assignee: Todd Lipcon
• Reporter: Todd Lipcon
• Created: 10/Sep/09 23:45
• Updated: 02/Nov/09 23:49
• Resolved: 02/Nov/09 23:49

Description

We experienced several jobs stuck in Reduce on a cluster. All of the stuck reduce tasks had a similar were stuck at "Need another 2 map output(s) where 0 is already in progress" despite all of the mappers having completed, and 0 scheduled. The stuck reducers had experienced the following exception early in the shuffle:

java.lang.NullPointerException
at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:768)
at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.getMapCompletionEvents(ReduceTask.java:2747)
at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.run(ReduceTask.java:2670)

Will attach more information and logs momentarily.