Manual:$wgSharedDB

Details
The name of the shared database.

Shared database for multiple wikis. Commonly used for storing a user table for single sign-on (actually not real SSO, since the user may still have to log in into each wiki separately, but at least registration has to be done only once). The server for this database must be the same as for the main database. From 1.13 on you may use $wgSharedPrefix to specify a separate prefix for this database.

*NOTE* This option and its related configuration options may not be compatible with databases other than MySQL.

See Manual:Shared database for usage information.