The MysqlUpdater class has the Mysql update list and mysql-specific update functions. The class contains the protected function getCoreUpdateList, which gets an array of updates to perform on the database. In the file, the contents of this array are organized sequentially by MediaWiki version number. There are 'addTable', 'addField', 'addIndex', 'dropTable', 'dropField', 'dropIndex', etc. elements which specify what is being changed and the sql files that implement the changes.

A number of maintenance scripts are run by the updater, usually in the format of $task = $this->maintenance->runChild( 'UpdateFoo' );