When you use hadoop jar [your_args]
to start your application, actually the real command is java -jar org.apache.hadoop.util.RunJar [your_args]
. So your driver which is used to start the MapReduce job is running in the process RunJar
.
By default mappers and reducers run as separate processes. You can not see it in JVisualVM is because JVisualVM does not have the correct permission. Mappers and reducers are launched under the user mapred
. So if you want to use JVisualVM, you need to use sudo -E -u mapred jvisualvm
.