For counter sampling, also called polling, the sFlow agent periodically polls the hardware interface statistics registers, counters, in the switch chip for per port statistics, and stores them in RAM until it is time to send the next message to the sFlow collector. Overall port statistics such as the number of broadcasts, errors, are collected by the sFlow agent.
The agent then includes the statistics in the sFlow datagrams sent to the sFlow collector along with the packet sampling information. From these statistics, the sFlow obtains information about the actual utilization of each port. For instance, information about broadcast to multicast to unicast rations is captured.
When you configure the agent for counter sampling, it sends an sFlow datagram at intervals of a second, at most. The datagram contains a snapshot of the counters cached in RAM from the most recent polling of interface counters.