protected function execute(InputInterface $input, OutputInterface $output)
   {
        $pool = $input->getArgument('pool');

        try {
            $this->memcache = $this->getContainer()->get('memcache.'.$pool);

            $output->writeln($this->memcache->flush()?'<info>OK</info>':'<error>ERROR</error>');
        } catch (ServiceNotFoundException $e) {
            $output->writeln("<error>pool '$pool' is not found</error>");
        }
   }