Question

Does wp.com create a new set of tables for each new blog, or are all blog data stored in one set of tables (with a layout like: http://codex.wordpress.org/Database_Description)?

Would it ever be a good idea to create a set of tables for each blog in MySQL, or will MySQL be able to handle large numbers of blogs each with their comments/tags/categories/posts stored in one set of tables?

Answer 1

For how WordPress does it, have a look at WordPress MU

I imagine at a quick guess there’s a shared user table and each blog gets it’s own DB as the relations between objects only apply within a individual blog.

Edit: From the MU FAQ:

WordPress MU creates tables for each
blog, which is the system we found
worked best for plugin compatibility
and scaling after lots of testing and
trial and error. This takes advantage
of existing OS-level and MySQL query
caches and also makes it infinitely
easier to segment user data, which is
what all services that grow beyond a
single box eventually have to do.