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

Tobias Oetiker tobi at oetiker.ch
Mon Nov 16 23:21:10 CET 2009


Today Marc MERLIN wrote:

> http://gargamel.merlins.org/cacti/graph.php?action=properties&local_graph_id=39&rra_id=0&view_type=tree&graph_start=1258302354&graph_end=1258315217
> and just in case my data samples were somehow bad (and I checked the source,
> they're not), the same thing happened at the same time on another data
> source at the same exact times:
> http://gargamel.merlins.org/cacti/graph.php?action=properties&local_graph_id=40&rra_id=0&view_type=tree&graph_start=1258302354&graph_end=1258315217
> There is just no way it's a concidence.
> Also I noticed that what shows up is a data sample with twice the value it
> should have and then the next sample is pretty much 0.
> The graph definitions are in the links and the rrd was created like so:
> /usr/bin/rrdtool create /var/lib/cacti/rra/housepower_21.rrd --step 120  \
> DS:HouseNoAC:DERIVE:600:-1000000000:1000000000 DS:House:DERIVE:600:-1000000000:1000000000 \
> DS:PGE:DERIVE:600:-1000000000:1000000000 DS:AC:DERIVE:600:-1000000000:1000000000 \
> DS:PV:DERIVE:600:-1000000000:1000000000 \
> RRA:AVERAGE:0.5:1:2628000 RRA:AVERAGE:0.5:1440:10950  RRA:AVERAGE:0.5:5:3153600 \
> RRA:AVERAGE:0.5:30:525600 RRA:AVERAGE:0.5:120:131400 \
> RRA:MAX:0.5:1440:10950 RRA:MAX:0.5:30:525600 RRA:MAX:0.5:120:131400 \
> I'm just trying to understand what could make these data problems possible.
> My original data on disk (before it was fed to the rrd) is correct.
> Even if there was a time delay in when the data was given, rrdtool knows how to interpolate
> data to make things right, so I don't get it.
> Any ideas?

you are talking about 'original' data, are you feeding the data to
rrdtool INCLUDING the collection time, or are you just using N: the
graph looks as if there was some bad case of jitter at work ...

two samples being 'faked' into one slot ...

> 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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