Minor Description
Currently every worker will start up a thread to communicate with every other workers. Hadoop RPC is used for communication. For instance if there are 400 workers, each worker will create 400 threads. This ends up using a lot of memory, even with the option
-Dmapred.child.java.opts="-Xss64k".
It would be good to investigate using frameworks like Netty or custom roll our own to improve this situation. By moving away from Hadoop RPC, we would also make compatibility of different Hadoop versions easier.
