# [rrd-users] Re: Combine gauge and counter

Alex van den Bogaerdt alex at ergens.op.het.net
Fri Jan 10 22:15:13 MET 2003

```On Fri, Jan 10, 2003 at 02:26:30PM -0500, PAUL WILLIAMSON wrote:

> I need to combine a gauge value and a counter value in one graph.  I've been
> messing around with how to do it and not being successful.

There's no such thing as graphing values.

*Everything* is a rate.  You tell RRDtool how to compute the rate:

- counter:  rate = (cur_value-last_value)/(cur_time-last-time)
- absolute: rate = (cur_value)/(cur_time-last-time)
- gauge:    rate = cur_value

There's also "derive".  This is like counter, with the difference
being that derive can result in negative rates whereas counter
will process the values as if a counter wrap occured.

MRTG also knows about counter, gauge and absolute.  I'm not sure
but I think MRTG doesn't know about derive.

After the collection phase, the rate is normalized and transfered
to each and every RRA in the RRD (or processed equivalent in MRTG).

vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv

> Next is to graph the rate.  RRDtool doesn't know nor care if the <
> rates were input as counter, absolute, gauge or derive.          <

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Yes, I consider this to be important :)

> I'd like to use MRTG as the collector, but I can obviously write my
> own collector if need be.

Then use MRTG.  One target is gauge, the other target is counter.
You may have to write your own grapher script to combine, say, the
ifInOctets of the 1st target with the ifOutOctets of the 2nd target.

Start by creating and graphing two unrelated targets. When you have
rates available, graph them on one graph.  If this isn't possible
due to their ranges this has nothing to do with counter, gauge or
whatother type of data source type.

HTH
Alex
--
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