public function createIndex($name, $table, $columns, $unique = false)
    {
        $description = 'create' . ($unique ? ' unique' : '') . " index $name on $table (" . implode(',', (array)$columns) . ')';
        $cmdPromise = $this->createCommand()->createIndex($name, $table, $columns, $unique)->execute();
        return $this->execPromise($cmdPromise, $description);
    }