I want to make a website which will have approximately 10M+ users. My MySQL database will be huge! Because the users will chat, post, share etc.

I will use dreamhost. They can provide me unlimted databases but they told me to keep the database size below 2-3GB. I'm afraid if I use a single database it will exceed 2-3GB in a week or two. 

So the question is - should I create a new database per user?