code: protected function _initMultiDbResources()
      {
          $registry = $this->getPluginResource('multidb');
          if (!$registry) {
              return;
          }
  
          //
          // options in configs/application
          $options = $registry->getOptions();
  
          foreach ($options as &$connection) {
              if ('db://' === substr($connection['dbname'], 0, 5)) {
                  $connection = array_replace(
                      $connection,
                      $this->_parseDsn($connection['dbname'])
                  );
              }
          }
  
          Zend_Registry::set('multidb', $registry->setOptions($options));
      }
docs: Initialize multidb resources.