[rrd-users] weird behaviour of rrd graph

Alex van den Bogaerdt alex at vandenbogaerdt.nl
Tue Sep 28 22:07:29 CEST 2010

> 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.


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