title: How to reduce number of mappers, when I am running hive query?
body: <p>I am using hive , </p>
  
  <p>I have 24 json files with total size of 300MB (in one folder), so I have created one external table(i.e table1)  and I loaded the data(i.e 24 files ) Into external table.</p>
  
  <p>When I am running select query on top of that external table(i.e table1), I observed 3 mappers and 1 reducer is running.</p>
  
  <p>After that I have created one more external table(i.e table2).</p>
  
  <p>I have compressed the my input files (folder which contains 24 files ).</p>
  
  <p>Example  : BZIP2 </p>
  
  <p>So it compress the data but 24 files created  with extension “.BZiP2”
  (i.e..file1.bzp2,…..file24.bzp2).</p>
  
  <p>After that , I have  load the my compressed files into my external table .</p>
  
  <p>Now, when I am running select query , it is taking 24 mappers and 1 reducer. And observed CPU time is taking more time when compared to uncompressed data(i.e files) .</p>
  
  <p>How can I reduce number of mappers, if data is in compressed format(i.e table2 select query )?  </p>
  
  <p>How can I reduce CPU time  , if data is in compressed format(i.e table2 select query )? How CPU time will affect performance?      </p>