[TACHYON-220] WIP Comments describing issues and possible solutions 

Some initial comments to help improve the performance of master info. From what I gather there is locking on stack local objects that are never really put back into the map. I would appreciate suggestions before implementing it, hence the WIP tag.
Ok perhaps using wrong terminology for copy. Once you do Inode inode= hashmap.get("someKey") change inode as much as you like but the value of "somekey" in the map is not overwritten until you do a hashmap.put("somekey",inode) . That's the point ,whey are we sync'ing to update inode and do all sorts of operations blocking the thread when it is on the stack and not shared between threads. Forget the lose terminology of "copy", there is just an overhead. If the map is concurrent we can do whatever we like to inode and only need sync when we put it back in to the shared map.

 HashMap<String , String > s= new ConcurrentHashMap();
    s.put("Hello","World");
    String p=s.get("Hello");
    p="Bye"; //some other operations
    System.err.println(s.get("Hello"));

Always prints "Hello World".  This is why its no point modifying p in a sync block! When we are ready to share state with other threads.

s.put(p); //synchronized!