Hive SQL 和 MR 异常之 reduce拉取数据失败

主要错误：

2016-12-23 09:43:10,656 INFO [fetcher#6] org.apache.hadoop.mapreduce.task.reduce.ShuffleSchedulerImpl: assigned 7 of 7 to hadoopserver04:13562 to fetcher#6
2016-12-23 09:43:10,656 INFO [fetcher#10] org.apache.hadoop.mapreduce.task.reduce.Fetcher: fetcher#10 - MergeManager returned status WAIT ...
2016-12-23 09:43:10,656 INFO [fetcher#10] org.apache.hadoop.mapreduce.task.reduce.ShuffleSchedulerImpl: hadoopserver10:13562 freed by fetcher#10 in 1455ms
2016-12-23 09:43:10,657 INFO [fetcher#10] org.apache.hadoop.mapreduce.task.reduce.ShuffleSchedulerImpl: Assigning hadoopserver10:13562 with 2 to fetcher#10
2016-12-23 09:43:10,657 INFO [fetcher#10] org.apache.hadoop.mapreduce.task.reduce.ShuffleSchedulerImpl: assigned 2 of 2 to hadoopserver10:13562 to fetcher#10
2016-12-23 09:43:10,657 WARN [main] org.apache.hadoop.mapred.YarnChild: Exception running child : org.apache.hadoop.mapreduce.task.reduce.Shuffle$ShuffleError: error in shuffle in fetcher#9
	at org.apache.hadoop.mapreduce.task.reduce.Shuffle.run(Shuffle.java:134)
	at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:376)
	at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:163)
	at java.security.AccessController.doPrivileged(Native Method)
	at javax.security.auth.Subject.doAs(Subject.java:422)
	at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1671)
	at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:158)
Caused by: java.lang.OutOfMemoryError: Java heap space
	at org.apache.hadoop.io.BoundedByteArrayOutputStream.(BoundedByteArrayOutputStream.java:56)
	at org.apache.hadoop.io.BoundedByteArrayOutputStream.(BoundedByteArrayOutputStream.java:46)
	at org.apache.hadoop.mapreduce.task.reduce.InMemoryMapOutput.(InMemoryMapOutput.java:63)
	at org.apache.hadoop.mapreduce.task.reduce.MergeManagerImpl.unconditionalReserve(MergeManagerImpl.java:305)
	at org.apache.hadoop.mapreduce.task.reduce.MergeManagerImpl.reserve(MergeManagerImpl.java:295)
	at org.apache.hadoop.mapreduce.task.reduce.Fetcher.copyMapOutput(Fetcher.java:514)
	at org.apache.hadoop.mapreduce.task.reduce.Fetcher.copyFromHost(Fetcher.java:336)
	at org.apache.hadoop.mapreduce.task.reduce.Fetcher.run(Fetcher.java:193)

主要错误信息：Error: org.apache.Hadoop.mapreduce.task.reduce.Shuffle$ShuffleError: error in shuffle in fetcher#43

解决办法：限制reduce的shuffle内存使用

                Hive：set mapreduce.reduce.shuffle.memory.limit.percent=0.1;

                MR：job.getConfiguration().setStrings("mapreduce.reduce.shuffle.memory.limit.percent", "0.1");

原理分析：reduce会在map执行到一定比例启动多个fetch线程去拉取map的输出结果，放到reduce的内存、磁盘中，然后进行merge。当数据量大时，拉取到内存的数据就会引起OOM，所以此时要减少fetch占内存的百分比，将fetch的数据直接放在磁盘上。

     mapreduce.reduce.shuffle.memory.limit.percent：每个fetch取到的map输出的大小能够占的内存比的大小。默认是0.25。因此实际每个fetcher的输出能放在内存的大小是reducer的Java heap size*0.9*0.25。