Does Wordpress.com use ONE set of tables for ALL users?

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 crea开发者_如何转开发te 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?

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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.