public function flushCacheNamespaces($ns_array = null)
    {
        if ($ns_array === null) {
            $ns_array = $this->getCacheNamespaces();
        }

        if ($this->flushable_cache instanceof SwatDBCacheNsFlushable) {
            $ns_array = array_unique($ns_array);
            foreach ($ns_array as $ns) {
                $this->flushable_cache->flushNs($ns);
            }
        }
    }