How to set the handler count related parameters?

[sam liu]

Hi,

We have 20 nodes cluster(1 namenode, 1 jobtracker, 18 datanodes).  Each
node has 20 cpu cores and 64 GB memory.

How to set the values for following parameters?

-

*dfs.namenode.handler.count- dfs.datanode.handler.count- *
*mapreduce.jobtracker.handler.count*
- *mapred.child.java.opts*

Thanks very much!