----- Original Message -----
From: "Jeff Gilmore" <[email protected]>
To: <[email protected]>
Sent: Wednesday, November 02, 2011 2:31 AM
Subject: [rrd-users] A plague of NaNs
> Hi all,
> I have an application where I read data from electric meters, each into its
> own RRD file storing only watts into a GUAGE. The RRD files are all of
> identical format, with a 60 second heartbeat.
> Most of the meters are read approximately once a minute, but that may vary by
> a few seconds (generally slightly longer than 60 seconds). These meters
> produce RRD files where 90+ percent of the values stored (as shown in the
> "database" section of RRDdump) are NaN.
Generally slightly longer than 60 seconds.
> One of the meters is set to upload data on 30 second intervals (but still
> feeds an RRD file with a 60 second heartbeat). The RRD for that meter has
> almost all of the values stored successfully.
And this one has no problems, 30 seconds being generously lower than 60 seconds.
> Can you help me understand why this might be the case?
As per the documentation:
heartbeat defines the maximum number of seconds that may pass between two
updates of this data source before the value of the data source is assumed to
be *UNKNOWN*.
Unknown, aka NaN.
You told rrdtool that updates further than 60 seconds apart are unreliable and
should be assumed to be unknown.
>
> I assumed that RRDtool's "normalization" process would adjust for the slight
> variations in timestamp between the actual data and the heartbeat interval of
> the RRD, fitting the update into the closest timeslot and adjusting the data
> value accordingly. It sounds like I don't understand it sufficiently,
> despite many hours searching the web on this topic.
It's not a sample rate, it's a heartbeat. If there is no heartbeat within
{$heartbeat} seconds, the subject is dead.
>
> In any case, I have a data source that produces data that is not perfectly
> aligned with the RRD heartbeat. Can you suggest how my application can deal
> with this and still take advantage of the power of RRDTool?
You confuse the step setting with the heartbeat setting. Read the tutorials,
see my site ( http://rrdtool.vandenbogaerdt.nl ) and play/experiment a bit with
settings.
good luck.
HTH
Alex
_______________________________________________
rrd-users mailing list
[email protected]
https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
