Manual:$wgSharedSchema

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

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;
}