What is MapReduce ? MapReduce is one of the most important and major component in Hadoop ecosystem. Whenever we are having a large set of data then in the case of the huge data set will be divided into smaller pieces and processing will be done on them in parallel in MapReduce. Multiple number of working nodes will be there on which this small pieces of this data sets will be assigned and processing would be done in parallel then the results will be obtained in the form of lists. MapReduce tests list as input and produces lists as output. This is the main purpose of MapReduce. ➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖ CAP Theorem | Consistency in NoSQL DBs Introduction to NoSQL | NoSQL Databases