Manual:$wgAllDBsAreLocalhost

Database settings: $wgAllDBsAreLocalhost
Make all database connections secretly go to localhost.
Introduced in version:	1.13.0 (r32818)
Removed in version:	1.28.0 (Gerrit change 311084; git #5bc9b990)
Allowed values:	(boolean)
Default value:	false
Other settings: Alphabetical | By function

Details

Make all database connections secretly go to localhost. Fool the load balancer thinking there is an arbitrarily large cluster of servers to connect to. Useful for debugging.

For example you might have a configuration like:

$wgLBFactoryConf = array(
 'class' => 'LBFactoryMulti',
 'sectionsByDB' => array(
    'wikidb' => 's1',
 ),
 'sectionLoads' => array(
    's1' => array(
        'localhost'  => 0,
        'somewhereElse'  => 0,
        'place20'  => 300,
        'place21'  => 300,
        'place3'  => 400,
        'place31'  => 400,
    ),
 ),
 'serverTemplate' => array(
    'dbname'      => $wgDBname,
    'user'          => $wgDBuser,
    'password'      => $wgDBpassword,
    'type'          => 'mysql',
    'flags'          => ( $wgDebugDumpSql ? DBO_DEBUG : 0 ) | DBO_DEFAULT,
    'max lag'      => 30,
    'fakeSlaveLag' => 1, // Needed since the "slaves" aren't really slaves
 ),
);
$wgAllDBsAreLocalhost = true;

Which would cause MediaWiki to behave like it had 6 db servers (1 master + 5 slaves), when really you just have the 1 DB on localhost.

See also

• Manual:$wgLBFactoryConf