[Xymon] Which RRD data type?

[Nelis, Wim]

On Tue, Oct 18, 2011 at 1:09 AM, Ward, Martin <Martin.Ward at colt.net> wrote:
> > I would like to have this graphed such that I can see the difference in each 5 minute interval.

> Isn't this what the COUNTER type is for?
There is a difference between what's been asked and what COUNTER does. The latter delivers the change per unit of time, thus the difference is divided by the interval length. The former is just the difference. As far as I know that is not possible with RRD. It would be possible if the length of the interval is available in an (rrdtool) variable, allowing one to compute (CDEF) and show the difference by multiplying the value with the length of the interval.

I once needed this feature to show the number of denied license requests. The total number of denied requests is in this case an important metric. There no nice solution I know of, even using a script which computes the difference (and handles counter wraps, and detects counter resets)  does not help. The computed value is presented to RRD as type GAUGE. However, for this type of measurement, you'll need another consolidation function, which could be called 'SUM'. The CF AVERAGE does um the values, but divides the result by the ratio of the interval lengths. This ratio is not available when generating a graph.

Regards,
  Wim Nelis.




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