title: MongoDB -- large number of documents
body: <p>This is related to my <a href="https://stackoverflow.com/questions/10191077/mongodb-large-number-of-databases">last question</a>.</p>
  
  <p>We have an app where we are storing large amounts of data per user. Because of the nature of data, previously we decided to create a new database for each user. This would have required a large no. of databases (probably millions) --  and as someone <a href="https://stackoverflow.com/questions/10191077/mongodb-large-number-of-databases#comment13082493_10191077">pointed out in a comment</a>, that this indicated wrong design.</p>
  
  <p>So we changed the design and now we are thinking about storing each user's entire information in one collection. This means one collection exactly maps to one user. Since there are 12,000 collections available per database, we can store 12,000 users per DB (and this limit could be increased).</p>
  
  <p>But, now my question is -- is there any limit on the no. of documents a collection can have. Because of the way we need to store data per user, we expect to have a huge (tens of millions in extreme cases) no. of document per documents. Is that OK for MongoDB and design-wise?</p>
  
  <p>EDIT</p>
  
  <p>Thanks for the answers. I guess then it's OK to use large no of documents per collection.</p>
  
  <p>The app is a specialized inventory control system. Each user has a large no. of little pieces of information related to them. Each piece of information has a category and some related stuff under that category. Moreover, no two collections need to see each other's data -- hence an index that touch more than one collection is not needed.</p>