May 26, 2021 Hadoop
The MRUnit unit tests the Mapper and Reducer classes run independently in memory, and the PipelineMapReduceDriver single thread runs.
LocalJobRunner runs on a single thread, and only one Reducer can start conf.set ("mapred.job.tracker," "local"); c onf.set("fs.default.name", "file:////"); FileSystem fs = FileSystem.getLocal(conf);
MiniMRCluster, MiniYarnCluster, MiniDFSCluster Multithreaded