[rrd-users] Adding an element to a graph

[Cole Tuininga]

On 3/1/07, Alex van den Bogaerdt <alex at ergens.op.het.net> wrote:
> On Thu, Mar 01, 2007 at 11:12:17AM -0500, Cole Tuininga wrote:
>
> > CDEF:placeholder=0
> > or, if necessary
> > CDEF:placeholder=0,0,+
> >
> > So that I can do a:
> >
> > LINE:placeholder#0000FF:Blah
> >
> > However, these don't seem to work.  It's not enough to simply add in
> > an "extra" item to the legend without graphing the data - this may be
> > the only item.  In that scenario, no graph would be generated, so
> > there would be no legend to add to.  :)
>
> Provided that your CDEF works, why would a graph not be created if you
> use LINE ?

I think I didn't explain myself well.  :)  Let me give it another shot.

Let's say my calling program was requesting a graph for dataset "A"
where "A" is formed by the potential aggregation of zero or more rrd
files and should have a label of "Dataset A".  In all cases where the
number of rrd files is >= 1, there is no problem.  I generate the DEF
lines, aggregate them with CDEFs, and then display them with LINE's or
AREA's as appropriate.  No problem.

The issue is that there are times where there are no rrd files
containing data pertinent to dataset A.  In this scenario, I would
still like to have a graph created, and to have "Dataset A" in the
legend.  The problem is that I can't seem to find a way to do this
when there are no rrd files to use as a source.  Just having a
constant value of 0 would be fine.  I can't just use an HRULE because
(correct me if I'm wrong) but that would not add the label into the
legend.

Does this help to make what I'm trying to do more clear?

-- 
Cole Tuininga
http://www.tuininga.org/