title: MapReduce Input/OutPut emits for each key value pair
body: <p>MapReduce basic information for passing and emiting key value pairs.
  I need little bit clarity what we pass and what emits.
  Here my concerns:
  MapReduce Input and OutPut:</p>
  
  <p>1.Map() method-Does it takes single or list of key-value pair and emits what?
  2.For each input key-value pair,what mappers emit ? Same type or different type ? 
  3.For each intermediate key ,what the reducer will emit ? Is there any restriction of type ?
  4.Reducer receives all values assocaited with same key.How the values will be ordered like sorted or orbitarly ordered ? Does that order vary from run to run ?
  5.During shuffle and sort phase,In which order keys and values are presented ?</p>