[rrd-users] Re: Manipulating and Graphing Data

Alex van den Bogaerdt alex at ergens.op.het.net
Tue Oct 31 01:08:37 MET 2006

On Mon, Oct 30, 2006 at 05:45:44PM -0600, Tony Varriale wrote:

> I am currently polling a qos drop queue and it returns the correct value. 
> The values are getting stored correct and everything looks great.

No, they ("the values") are not stored.

This wrong assumption is probably the foundation of the rest of your
work, so all is flawed.

You don't store numbers in an RRD.  Rates are stored, and they are
not the ones you put in.  See my site, see the tutorials, see the

> GPRINT:a:MAX:"Max\:%8.2lf%s" What I would like to graph as "current" is the 
> (current value - the previous value) in the RRA. This will give me the 
> amount of change since the last interval.  I assumed I could do this via a 
> CDEF but I am not sure how to get the previous value to do the subtraction.

For this, RRDtool has the "DERIVE" counter type.

Alex van den Bogaerdt

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