title: Maximum number of paths Map side join can join?
body: <p>What is the maximum number of paths Map side join can actually join?</p>
  
  <p>I have <strong>n</strong> folders - path/to/folder1 , path/to/folder2 , path/to/folder3 ....so on path/to/foldern in HDFS</p>
  
  <p>path/to/folder1 contains 3 files, say part-1,part-2,part-3.Similarly,each of all the remaining folders have 3 files each with same names as in folder1.</p>
  
  <p>I want to join these folders using map side join like below</p>
  
  <p>pathsToJoin &lt;- path/to/folder1 , path/to/folder2 , path/to/folder3 ....so on path/to/folder*<em>n</em>*</p>
  
  <p>String joinStmt = CompositeInputFormat.compose("outer",TextInputFormat,pathsToJoin);</p>
  
  <p>conf.set("mapred.join.expr", joinStmt);</p>
  
  <p>Since there are 3 files in each folder,the job will spawn 3 map tasks (content of all part-1 files joined to one mapper,content of all part-2 files to 2nd mapper and content of all part-3 files to 3rd mapper) but I would like to know what can be the max value of <strong>n</strong> here?</p>