title: Is it possible to know the serial number of the block of input data on which map function is currently working?
body: <p>I am a novice in Hadoop and here I have the following questions:</p>
  
  <p>(1) As I can understand, the original input file is split into several blocks and distributed over the network. Does a map function always execute on a block in its entirety? Could there be more than one map functions executing on data in a single block?</p>
  
  <p>(2) Is there any way that it can be learned, from within the map function, which section of the original input text the mapper is currently working on? I would like to get something like a serial number, for instance, for each block starting from the first block of the input text.</p>
  
  <p>(3) Is it possible to make the splits of the input text in such a way that each block has a predefined word count? If possible then how?</p>
  
  <p>Any help would be appreciated.</p>