flush_all (MemCache)

    # File lib/active_support/vendor/memcache-client-1.7.4/memcache.rb, line 497
      def flush_all(delay=0)
        raise MemCacheError, 'No active servers' unless active?
        raise MemCacheError, "Update of readonly cache" if @readonly

        begin
          delay_time = 0
          @servers.each do |server|
            with_socket_management(server) do |socket|
              logger.debug { "flush_all #{delay_time} on #{server}" } if logger
              if delay == 0 # older versions of memcached will fail silently otherwise
                socket.write "flush_all#{noreply}\r\n"
              else
                socket.write "flush_all #{delay_time}#{noreply}\r\n"
              end
              break nil if @no_reply
              result = socket.gets
              raise_on_error_response! result
              result
            end
            delay_time += delay
          end
        rescue IndexError => err
          handle_error nil, err
        end
      end