Manual:$wgSharedSchema

Shared DB settings: $wgSharedSchema
The table schema for the shared database
Introduced in version:	1.23.0 (Gerrit change 173063; git #I291e770)
Removed in version:	Still in use
Allowed values:	(boolean)
Default value:	`false`
Other settings: Alphabetical \| By function

Details

If set to false, it'll fallback to the value of $wgDBmwschema . This fallback is set in Setup.php .

// Set default shared schema
if ( $wgSharedSchema === false ) {
	$wgSharedSchema = $wgDBmwschema;
}