public function getDiff()
    {
        $set = $this->getIndexInfo();
        unset($set['_id_1']);

        $present = array();
        $missing = array();

        foreach ($this->config as $index) {
            if ( !isset($index['options']) ) $index['options'] = array();

            $name = $this->generateIndexKeyFromConfig($index);
            if ( isset($set[$name]) ) {
                $present[$name] = $index;
                unset($set[$name]);
            } else {
                $missing[$name] = $index;
            }
        }

        return array(
            'missing' => $missing,
            'present' => $present,
            'unknown' => $set
        );
    }