Does WordPress MultiSite use separate MySql databases?

Question

I ask because I cannot find the options from a plug-in I created on my second blog.

Adding this plug-in to the main site and the options show up.

I am confused because there is a column in wp_options table blog_id and I was expecting there to be more than one value there.

Answer 1

WordPress MU uses one database and each blog gets his own tables with the blog id in the prefix, so once you install a network installation your database should have these tables:

• wp_1_categories
• wp_1_comments
• wp_1_link2cat
• wp_1_links
• wp_1_options
• wp_1_post2cat
• wp_1_postmeta
• wp_1_posts
• wp_blogs
• wp_blog_versions
• wp_registration_log
• wp_signups
• wp_site
• wp_sitecategories
• wp_sitemeta
• wp_usermeta
• wp_users

And every new site you set up will create separate tables for example:

• wp_2_categories
• wp_2_comments
• wp_2_link2cat
• wp_2_links
• wp_2_options
• wp_2_post2cat
• wp_2_postmeta
• wp_2_posts

Answer 2

Although WordPress MU requires just a single database, as seen on WordPress Codex, you can always use different databases if you prefer to.

Plugins such as Multi-DB allow you to do so, and although this wouldn't be much needed for a small-medium network, it would be interesting for large setups.