Relationship between heap sizes and mapred.child.java.opt configuration

I'm learning about Hadoop configuration. What is the connection between the datanode/ tasktracker heap sizes and the mapre.child.java.opts? Does one have to be exceeded to another?

Re: Relationship between heap sizes and mapred.child.java.opt configuration

mapred.child.java.opts are referring to the settings for the JVMs spawned by the TaskTracker. This JVMs will actually run the tasks (mappers and reducers) The heap sizes for TaskTrackers and DataNodes are unrelated to those. They run in their own JVMs each. Kai Am 25.11.2013 um 15:52 schrieb

Re: Relationship between heap sizes and mapred.child.java.opt configuration

Thanks for the reply. So what is the purpose of heap sizes for tasktrackers and datanodes then? In other words, if I want to speed up the map/reducing cycle, can I just minimize the heap size and maximize the mapred.child.java.opts? or will the minimizing heap sizes causing out of memory