I think it is very good for me to understand Hadoop in detail if I can debug the real working mechanism of namenode and datanode in either pseudo-distributed or fully-distributed mode.
I think that apaceh hadoop team or.. any major developers of hadoop, hdfs or mapreduce can do this, but there is no document mentioning this method.
Every document mentioned how we can debug mapreduce with eclipse in local environment. This meanse LocalJopRunner is running and we can see that how LocalJobRunner run.
Thanks.