[rrd-users] peak after NaN?

[Tobias Oetiker]

Today Nuno Gonçalves wrote:

> I have a rrdtool database created with:
>
> >rrdtool create "$rrdfile" --step 60 DS:pressure:GAUGE:90:0:1100 DS:temperature:GAUGE:90:-50:100 DS:humidity:GAUGE:90:0:100
>
> The samples are entered in 60s steps with:
>
> >rrdtool update "$rrdfile" N:$P:$T:$H
>
> After a computer restart, that made 2 missed samples, I noticed a
> down-peak on the graph and did a rrdtool fetch to check:
>
> >1239617640: 9.9586069400e+02 1.7373722021e+01 5.6504290012e+01
> >1239617700: 9.9586000000e+02 1.7776053280e+01 5.7130494367e+01
> >1239617760: nan nan nan
> >1239617820: nan nan nan
> >1239617880: 9.8159131106e+02 1.9585499172e+01 4.9668510483e+01
> >1239617940: 9.9584083364e+02 2.0126658206e+01 5.0490830009e+01
> >1239618000: 9.9583079547e+02 2.0435340373e+01 5.1061476218e+01
>
> The same samples are also recorded to a text file to I could confirm
> that it was not a sensor problem, the values feed to rrdtool where
> between 996.1-995.8.
>
> In >1239617880: 9.8159131106e+02 1.9585499172e+01 4.9668510483e+01,
> where did come the 981.59?

Hi Nuno,

the first sample after an interval longer than MRHB is used simply
to re-enable data entry. The reason for this is, that rrdtool
associates a 'timespan' with each update, and if the time since the
last update is longer the mrhb then it can't and will thus ignore
the value of the update.

hth
tobi

>
> Thanks,
> Nuno
>
> rrdtool 1.2.30
>
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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