[HADOOP-2486] Dropping records at reducer. InMemoryFileSystem NPE.

• Type: Bug
• Status: Closed
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: 0.14.3
• Fix Version/s: 0.15.2
• Assignee: Devaraj Das
• Reporter: Koji Noguchi
• Created: 22/Dec/07 06:38
• Updated: 08/Jul/09 16:52
• Resolved: 26/Dec/07 08:40

Description

Note: I'm really not sure if this is a bug in my code or in mapred.

With my mapreduce job without combiner, I sometimes see # of total Map output records != # of total Reduce input records. What's weird to me is, when I rerun my code with exact same input, usually I get an expected #map output recs == #reduce output recs.

Both jobs finish successfully. No failed tasks. No speculative execution.

I ran separate linecount mapred jobs on both the input and the output to see if the counters are reporting the correct number.

When I looked at all the 513 reducer counter, I found single reducer with different counts for the two runs.
Only error stood out in that reducer userlog is,

 
2007-12-22 00:19:07,640 INFO org.apache.hadoop.mapred.ReduceTask: task_200712220008_0003_r_000024_0 done copying task_200712220008_0003_m_000288_0 output from qqq856.ppp.com.
2007-12-22 00:19:07,640 INFO org.apache.hadoop.mapred.ReduceTask: task_200712220008_0003_r_000024_0 Copying task_200712220008_0003_m_000327_0 output from qqq887.ppp.com.
2007-12-22 00:19:07,640 ERROR org.apache.hadoop.mapred.ReduceTask: Map output copy failure: java.lang.NullPointerException
	at org.apache.hadoop.fs.InMemoryFileSystem$RawInMemoryFileSystem$FileAttributes.access$300(InMemoryFileSystem.java:366)
	at org.apache.hadoop.fs.InMemoryFileSystem$RawInMemoryFileSystem$InMemoryFileStatus.(InMemoryFileSystem.java:380)
	at org.apache.hadoop.fs.InMemoryFileSystem$RawInMemoryFileSystem.getFileStatus(InMemoryFileSystem.java:283)
	at org.apache.hadoop.fs.FileSystem.isDirectory(FileSystem.java:423)
	at org.apache.hadoop.fs.ChecksumFileSystem.rename(ChecksumFileSystem.java:386)
	at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.copyOutput(ReduceTask.java:716)
	at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.run(ReduceTask.java:637)

2007-12-22 00:19:07,641 INFO org.apache.hadoop.mapred.ReduceTask: task_200712220008_0003_r_000024_0 done copying task_200712220008_0003_m_000228_0 output from qqq801.ppp.com.
2007-12-22 00:19:07,641 INFO org.apache.hadoop.mapred.ReduceTask: task_200712220008_0003_r_000024_0 Copying task_200712220008_0003_m_000337_0 output from qqq841.ppp.com.

Could this error be somehow related to my having different # of records?