title: One big table or many small tables
body: <p>I am developing a website (WordPress MU - based). In this website, users can create their own blogs, can fully customize their own blogs (change background, write articles...), add more users to their blogs...</p>
  
  <p>The most common query is to get articles of a blog. 2 different blogs are almost not related.</p>
  
  <p>The information of the blogs can be stored in database in 2 ways:</p>
  
  <ol>
  <li>A few tables containing all the information, each blog is identified
  by blog_id.</li>
  <li>Many groups of tables. Each group of tables contains all information of a blog. More blogs, create more tables.</li>
  </ol>
  
  <p>My questions are:</p>
  
  <ol>
  <li>In term of performance, which one is better?</li>
  <li>WordPress actually uses the second design. If the number of blogs
      is    very large (thousands) then the number of tables can be
  tens
      of    thousands. Does this cause any problem? Is there a limit
  of
      number of    tables of a MySQL database?</li>
  </ol>