[rrd-users] Debugging graph smoothing or bad data samples? interpolation bug?

Tobias Oetiker tobi at oetiker.ch
Tue Nov 17 22:25:48 CET 2009

Hi Marc,

Today Marc MERLIN wrote:

> On Tue, Nov 17, 2009 at 06:50:40AM +0100, Tobias Oetiker wrote:
> > Hi Marc,
> >
> > > Does that make any sense to you?
> >
> > not entirely, I can only say that irregular data arrival times are
> > rrdtools forte ... have you tried to write the data into a logfile
> > (including the timestamp) and then recreate the phaenomenon by hand ?
> I have all the data in a logfile already, this is where I read it from :)
> (script writes to logfile, cacti polls logfile from cron and feeds to
> rrdtool).
> I have another script that will dump the entire logfile, generate a log list
> of rrdtool update statements and I can recreate the entire rrd from scratch
> after erasing it and replaying all the events.

ah ... in that case it is clear ... sometimes, you have one update
in the file and sometimes two by the time cacti comes around ...a
very bad case of jitter ... you should realy make it so that cacti
can trigger the data accqusition ...


> Is that what you meant?
> If so, it'll fix it for sure, the data looks good, but of course I won't be
> exercising the same code in rrdtool update since the rebuild way recreates
> the rrd by sending time/data tuples that are all exactly 2mn apart.
> I'm not too sure how else I can recreate whatever may have happened here.
> Can you explain in more details what you had in mind?

> Thanks,
> Marc

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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