title: mongodb - many documents in one collection vs many collection
body: <p>I'm using mongodb as database storage. </p>
  
  <p>my web app has to collect user responses.</p>
  
  <p>a user response is a document in mongodb (or a row in sql). length of a document is about 10~200.</p>
  
  <p>user responses are categorized(to only one category). for each category, number of user response is between 100~5000. if two document is in same category, the have same length. (or they have same columns in sql)</p>
  
  <p>a category can be dynamically created/deleted by request of admins.</p>
  
  <p>currently, my data structue is</p>
  
  <pre><code>category collection
  {_id, 'name' : 'c1', 'somevalue' : '123'}
  {_id, 'name' : 'c2', 'somevalue' : '23'}
  {_id, 'name' : 'c3', 'somevalue' : '143'}
  {_id, 'name' : 'c4', 'somevalue' : '153'}
  ...
  
  'c1' collection
  { userresponse1 }
  { userresponse2 }
  { userresponse3 }
  ...
  
  'c2' collection
  { userresponse1 }
  { userresponse2 }
  { userresponse3 }
  ...
  
  'c3' collection
  { userresponse1 }
  { userresponse2 }
  { userresponse3 }
  ...
  
  'cN' collection
  { userresponse1 }
  { userresponse2 }
  { userresponse3 }
  ..
  </code></pre>
  
  <p>Is this a wise decision? I'm worried about possibility of something going bad by assigning a collection for each category. will there be some performance issues if I have many collections? should I merge my collections and give the userresponses some identifiers instead? </p>