Job will fail randomly

[Liu-Delin]

We have two arguments to set memory when run shifu stats.

1. -Dmapreduce.map.memory.mb=4096
2. -Dmapreduce.map.java.opts="-Xms3700m -Xmx3700m -server -XX:MaxPermSize=64m -XX:PermSize=64m -XX:+UseParallelGC -XX:+UseParallelOldGC -XX:ParallelGCThreads=8 -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCTimeStamps"

It means that the worker has 4096MB and JVM has 3700MB memory. But sometimes it will fail due to physical memory is not enough, and we can set less JVM memory to avoid this issue.