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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