If you don’t no what is starting and ending point/lines, it’s much difficult to solve those problems. Setup and clean up can resolve it. N number of blocks, by default 1 mapper called to each split. each split has one start and clean up methods. N number of methods, number of lines. Setup is initialize job resources. The purpose of clean up is close the job resources. Map is process the data. once last map is completed, cleanup is initialized. It Improves the data transfer performance. All these block size comparison can do in reducer as well. If you have any key and value, compare one key value to another key value use it. If you compare record level used these setup and cleanup. It open once and process many times and close once. So it save a lot of network wastage during process.
