[rrd-users] Graphing integer data in Cacti/RRDTool

Tobias Oetiker tobi at oetiker.ch
Thu Jun 12 07:26:19 CEST 2008

Hi Nick,

Yesterday Nick Ellson wrote:

> I have been point to RRD-Tool as the possible cause of an artifact I am
> seeing in my Cacti graphs of a Cisco ASA VPN Connection Count OID.  If I
> understand what it happening, the squarewave looking graphs I had in MRTG
> showing the number of remote users currently logged in, is not possible
> with RRD Tool, because as the 5 min samples are taken, and an integer
> value is retrieved but more that 10 secs past the 5 min sampling window
> then RRD Tool will interpolate the value to what it could have been at the
> 5 min interval.
> Hence I have a very analog looking graph of my VPN User count with my
> current connection count being 3.2 users, with a high today of 9.83.
> Is this something that can be adjusted in some way to allow this OID to be
> treated as an absolute interger?

If you tell rrdtool that you had 5 users from 11:58-12:04 and then
3 users from 12:04 - 12:09. What number should rrdtool write into
the slot from 12:00 - 12:05 ?

I guess, what you want todo, is to lie to rrdtool about the
acquisition time of your data. So instead of 12:04 to 12:09 you
should tell it that the data was for 12:05 to 12:10. But then
again, maybe you want to take the data as exact as it gets and this
is unfortunately 'with comma' if you have fixed sampleing times for
discreet events that happen in analog time.


Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten
http://it.oetiker.ch tobi at oetiker.ch ++41 62 213 9902

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