[rrd-users] weird behaviour of rrd graph

Tobias Oetiker tobi at oetiker.ch
Tue Sep 28 22:14:25 CEST 2010

Today Alex van den Bogaerdt wrote:

> > every night the yearly graph is generated and looks ok:
> > http://umweltsuen.de/tmp/power-1y-ok.png
> >
> > there is only one exception:
> > from time to time, the resolution of the graph changes, and it looks like
> > this:
> > http://umweltsuen.de/tmp/power-1y-wrong.png
> > (this happened twice now, after more than 1 1/2 months without problems)
> > maybe someone has an explanation, what`s causing this effect and how to
> > avoid it ?
> Yeah, it has to do with resolution, with availability of data, with the best
> match on what you ask, not what you want to ask, but actually do ask.
> RRDtool has a choice which RRA to use, and it chooses one you don't like.
> But for some reason that RRA is actually a closer match to what you ask than
> the other which is used in all other cases.
> To avoid: determine from which RRA you want the data to be displayed. Set
> your end time to a time which is on a boundary, a whole multiple of
> step*steps, a duration of a CDP.

also note that recent rrdtool versions have become more 'stable' in
their choices ... by only looking to the past and not to the
present since all RRAs by definition cover the present to the best
of their abilities ...


> Alex
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> rrd-users at lists.oetiker.ch
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Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 9902 / sb: -9900

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