Manual:$wgSharedDB

Shared DB settings: $wgSharedDB
The name of the shared database.
Introduced in version:1.4.0
Removed in version:still in use
Allowed values:Unspecified
Default value:null

Details edit

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.

This option and its related configuration options may not be compatible with databases other than MySQL. Support for SQLite was added in MediaWiki 1.17. Support for PostgreSQL was added in MediaWiki 1.19.

See Manual:Shared database for usage information.

MediaWiki 1.39 incorrectly gives a deprecation warning during update.php for this config. The warning can be ignored. [1]
  Caution: Renameuser is currently incompatible with $wgSharedDB. See phab:T104830.

See also edit