一. 问题描述

今天跑一个MR任务，数据量不大，跑了半个小时左右，遇到了超时的报错

报错信息:

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:136) at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:377) at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:174) 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:1875) at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:168) Caused by: java.lang.OutOfMemoryError: Java heap space at org.apache.hadoop.io.BoundedByteArrayOutputStream.<init>(BoundedByteArrayOutputStream.java:56) at org.apache.hadoop.io.BoundedByteArrayOutputStream.<init>(BoundedByteArrayOutputStream.java:46) at org.apache.hadoop.mapreduce.task.reduce.InMemoryMapOutput.<init>(InMemoryMapOutput.java:60) at org.apache.hadoop.mapreduce.task.reduce.MergeManagerImpl.unconditionalReserve(MergeManagerImpl.java:313) at org.apache.hadoop.mapreduce.task.reduce.MergeManagerImpl.reserve(MergeManagerImpl.java:303) at org.apache.hadoop.mapreduce.task.reduce.Fetcher.copyMapOutput(Fetcher.java:532) at org.apache.hadoop.mapreduce.task.reduce.Fetcher.copyFromHost(Fetcher.java:342) at org.apache.hadoop.mapreduce.task.reduce.Fetcher.run(Fetcher.java:198)

二. 解决方案

调整参数即可

mapreduce.reduce.shuffle.memory.limit.percent=0.1 # 默认是0.25 可以在代码里面设置，也可以在mapred-site.xml文件配置,这个参数的意思是说reduce每次fetceh数据的时候，达到reduce jvm内存的百分之多少的时候，就把数据写入到磁盘