MapReduce is submitted to Yarn for general execution of the process.
Start the application to submit a job (wordcount.jar and the configuration parameters and data slicing planning files in the program) to run the process as runjar
ResouceManager will first start the supervisor process MRAppMasster of the customer-submitted wordcount.jar on a node NodeManager
The mapTask task (yarnChild process) is started by the supervisor process (MRAppMasster) according to the startup rules. If all mapTask tasks run to an end, the MRAppMasster process starts the Reduce Task task (the yarnChild process)
