求救CDH5.3.0跑mapreduce,报错误

求救CDH5.3.0跑mapreduce,报错误如下，能搞定的话可长期做我们的顾问，非常感谢！：
map可以成功完成，但reduce报错，详情见附件日志。
Error: org.apache.hadoop.mapreduce.task.reduce.Shuffle$ShuffleError: error in shuffle in fetcher#4
        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:168)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:415)
        at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1642)
        at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:163)
Caused by: java.lang.NoClassDefFoundError: Ljava/lang/InternalError
        at org.apache.hadoop.io.compress.snappy.SnappyDecompressor.decompressBytesDirect(Native Method)
        at org.apache.hadoop.io.compress.snappy.SnappyDecompressor.decompress(SnappyDecompressor.java:239)：

解决办法：
修改mapred-site.xml配置中的mapreduce.reduce.shuffle.memory.limit.percent参数
[mw_shl_code=bash,true]<property>
   <name>mapreduce.reduce.shuffle.memory.limit.percent</name>
  <value>0.25</value>
  <description>Expert: Maximum percentage of the in-memory limit that a
  single shuffle can consume</description>
</property>
[/mw_shl_code]


这个值默认是0.25，适当的减小这个值。