What I talk about when I talk about NameNode JMX
So I asked an elephant keeper, for a too many under-replicated blocks problem, please check the NameNode status via JMX. He found the JMX returned too verbose, and he was not sure what were the most important JMX metrics. I remember the old naive days when myself just started working on HDFS and troubleshooting NameNode issues, I was also wondering which JMX metrics were majory or general. I don’t keep my list secret so here it is.