Multiple snmp requests for the same MIB OID

[ahof]

When cacti poll a device, it sends multiple (atleast 2) snmp requests for the same MIB OID. It produce a high CPU load on a network device.

Were can I set set the counter to send only one request to the device.
Is it also possible to ping the device for availablity and 5min interval for snmp. Because, when you use ping for availability, the graphs don't functioning anymore.