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From "Jacob Rideout (JIRA)" <j...@apache.org>
Subject [jira] Created: (MAPREDUCE-1571) OutOfMemoryError during shuffle
Date Sun, 07 Mar 2010 20:18:27 GMT
OutOfMemoryError during shuffle
-------------------------------

                 Key: MAPREDUCE-1571
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1571
             Project: Hadoop Map/Reduce
          Issue Type: Bug
    Affects Versions: 0.20.2, 0.20.1
            Reporter: Jacob Rideout


A OutOfMemoryError can occur when determining if the shuffle can be accomplished in memory

2010-03-06 07:54:49,621 INFO org.apache.hadoop.mapred.ReduceTask:
Shuffling 4191933 bytes (435311 raw bytes) into RAM from
attempt_201003060739_0002_m_000061_0
2010-03-06 07:54:50,222 INFO org.apache.hadoop.mapred.ReduceTask: Task
attempt_201003060739_0002_r_000000_0: Failed fetch #1 from
attempt_201003060739_0002_m_000202_0
2010-03-06 07:54:50,223 WARN org.apache.hadoop.mapred.ReduceTask:
attempt_201003060739_0002_r_000000_0 adding host
hd37.dfs.returnpath.net to penalty box, next contact in 4 seconds
2010-03-06 07:54:50,223 INFO org.apache.hadoop.mapred.ReduceTask:
attempt_201003060739_0002_r_000000_0: Got 1 map-outputs from previous
failures
2010-03-06 07:54:50,223 FATAL org.apache.hadoop.mapred.TaskRunner:
attempt_201003060739_0002_r_000000_0 : Map output copy failure :
java.lang.OutOfMemoryError: Java heap space
       at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.shuffleInMemory(ReduceTask.java:1508)
       at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.getMapOutput(ReduceTask.java:1408)
       at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.copyOutput(ReduceTask.java:1261)
       at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.run(ReduceTask.java:1195)


Ted Yu identified the following potential solution:

I think there is mismatch (in ReduceTask.java) between:
     this.numCopiers = conf.getInt("mapred.reduce.parallel.copies", 5);
and:
       maxSingleShuffleLimit = (long)(maxSize *
MAX_SINGLE_SHUFFLE_SEGMENT_FRACTION);
where MAX_SINGLE_SHUFFLE_SEGMENT_FRACTION is 0.25f

because
     copiers = new ArrayList<MapOutputCopier>(numCopiers);
so the total memory allocated for in-mem shuffle is 1.25 * maxSize

A JIRA should be filed to correlate the constant 5 above and
MAX_SINGLE_SHUFFLE_SEGMENT_FRACTION.

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