title: How can i sort large csv file without loading to memory
body: <p>I have 20GB+ csv file like this:</p>
  
  <pre><code>**CallId,MessageNo,Information,Number** 
  1000,1,a,2
  99,2,bs,3
  1000,3,g,4
  66,2,a,3
  20,16,3,b
  1000,7,c,4
  99,1,lz,4 
  ...
  </code></pre>
  
  <p>I must order this file by CallId and MessageNo as asc. (One way is load database->sort->export)</p>
  
  <p>How can i sort this file without loading all lines to memory in c#? (like line by line using streamreader)</p>
  
  <p>Do you know a library for solution?
  i wait your advice,
  thanks</p>