title: MemoryError when I merge two Pandas data frames
body: <p>I searched almost all over the internet and somehow none of the approaches seem to work in my case. </p>
  
  <p>I have two large csv files (each with a million+ rows and about 300-400MB in size). They are loading fine into data frames using the <em>read_csv</em> function without having to use the <em>chunksize</em> parameter.
  I even performed certain minor operations on this data like new column generation, filtering, etc.</p>
  
  <p>However, when I try to merge these two frames, I get a <strong>MemoryError</strong>. I have even tried to use SQLite to accomplish the merge, but in vain. The operation takes forever. </p>
  
  <p>Mine is a Windows 7 PC with 8GB RAM. The Python version is 2.7</p>
  
  <p>Thank you.</p>
  
  <p>Edit: I tried chunking methods too. When I do this, I don't get MemoryError, but the RAM usage explodes and my system crashes.</p>