[rrd-users] Re: meaning of "min" and "max" for COUNTER data sources?

[Alex van den Bogaerdt]

On Wed, Jul 07, 2004 at 06:14:13PM +0200, ciaran deignan wrote:

> The RRD documentation "reccomends" setting MIN and MAX values for
> all data-sources when creating the RRD files. But all the examples
> show this with a GUAGE DS-type, where MAX is obviously the biggest value
> the counter can ever hold.

Rates, not datasources.

> How is MAX interpreted for a COUNTER DS-type? Does it represent the
> maximum increment over the previous data-point? What if the previous
> data-point is two "steps" back in time? Is the MAX a maximum per-step
> increment? Or is it configured as a rate directly and multiplied by
> the step interval and the number of steps?

Everything in an RRA is a rate.  DSes are used to compute the rate.

A DS of GAUGE (note: not GUAGE) means the number already _is_ a rate.

For a COUNTER:
If you skip a step or two, and if heartbeat allows to update anyway, the
rate is still computed as (counter_now-counter_then)/(time_now-time_then).

For all DSes:
The resulting rate, after normalization, is checked against min and max.

> For example, I'm just starting to experiment with RRD, and I'm logging
> sysUpTime from SNMP as a sanity check. The rate-of-change of the counter
> is one-second-per-second ;) Should I declare the DS as
> 
>     rrdtool create --step 60 DS:sysUpTime:COUNTER:360:0:60
> or
>     rrdtool create --step 60 DS:sysUpTime:COUNTER:360:0:1
> ???

Is uptime in seconds?  If so, I guess 1 is the appropriate value, however
I would add a few percent to cope with rounding errors.

HTH
Alex
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