MergeManager.reserve can OutOfMemoryError if more than 10% of max memory is used on non-MapOutputs

The MergeManager does a memory check, using a limit that defaults to 90% of Runtime.getRuntime().maxMemory(). Allocations that would bring the total memory allocated by the MergeManager over this limit are asked to wait until memory frees up. Disk is used for single allocations that would be over 25% of the memory limit.

If some other part of the reducer were to be using more than 10% of the memory. the current check wouldn't stop an OutOfMemoryError.

Before creating an in-memory MapOutput, a check can be done using Runtime.getRuntime().freeMemory(), waiting until memory is freed up if it fails.

12/08/17 10:36:29 INFO mapreduce.Job: Task Id : attempt_1342723342632_0010_r_000005_0, Status : FAILED
Error: org.apache.hadoop.mapreduce.task.reduce.Shuffle$ShuffleError: error in shuffle in fetcher#6
at org.apache.hadoop.mapreduce.task.reduce.Shuffle.run(Shuffle.java:123)
at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:371)
at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:152)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:416)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1232)
at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:147)
Caused by: java.lang.OutOfMemoryError: Java heap space
at org.apache.hadoop.io.BoundedByteArrayOutputStream.<init>(BoundedByteArrayOutputStream.java:58)
at org.apache.hadoop.io.BoundedByteArrayOutputStream.<init>(BoundedByteArrayOutputStream.java:45)
at org.apache.hadoop.mapreduce.task.reduce.MapOutput.<init>(MapOutput.java:97)
at org.apache.hadoop.mapreduce.task.reduce.MergeManager.unconditionalReserve(MergeManager.java:286)
at org.apache.hadoop.mapreduce.task.reduce.MergeManager.reserve(MergeManager.java:276)
at org.apache.hadoop.mapreduce.task.reduce.Fetcher.copyMapOutput(Fetcher.java:327)
at org.apache.hadoop.mapreduce.task.reduce.Fetcher.copyFromHost(Fetcher.java:273)
at org.apache.hadoop.mapreduce.task.reduce.Fetcher.run(Fetcher.java:153)