Can someone please explain how does ‘map’ and ‘reduce’ work in HDFS?
Map and Reduce functioning in Hadoop: The Namenode takes the input and divide it into parts and assign them to data nodes. These datanodes process the tasks assigned to them and make a key-value pair and returns the intermediate output to the Reducer. The reducer collects this key value pairs of all the datanodes and combines them and generates the final output. This is how Map and Reduce will work for any size of data volume.