[rrd-users] Graphing Sparse Data

Laack,Jacob C JLaack at alegent.org
Wed May 14 17:33:23 CEST 2008

The RRD data is compiled in 4 hour, 24 hour, 1 week, 1 month and 1 year durations.  The data is plotted about every 6 hours rather than at specific times.  That's just how nagios works.  All of my graphs for the above durations are blank.  If I force a check (manually get a data point) a couple times, I get a small pixel or two long line.  But the next day, my graphs have no dots or lines afterwards even though 2 or 3 points of data are in there somewhere.

I thought about your last paragraph...  If my checks are 6 hours apart and my shortest RRD is 4 hours, wouldn't that pretty much keep the RRD's empty most of the time?  If that is a stupid question, my goal would be to simply draw lines between the points.

I'm going to make my polling interval 2 hours and see what kind of graphs I get.  Thanks for your insight.

-----Original Message-----
From: rrd-users-bounces at lists.oetiker.ch [mailto:rrd-users-bounces at lists.oetiker.ch] On Behalf Of Simon Hobson
Sent: Wednesday, May 14, 2008 10:19 AM
To: rrd-users at lists.oetiker.ch
Subject: Re: [rrd-users] Graphing Sparse Data

Laack,Jacob C wrote:

>I am monitoring many services with Nagios and the data ends up in
>RRDs which I graph using pnp.  (I promise this is an rrd question.)
>One type of service is only checked every 6 hours (instead of the
>normal 5 minutes) so only 4 pieces of data are put into the RRD file
>a day.  rrdgraph shows empty graphs for 4 and 24 hours since the
>data is so sparse.  Would it be possible to use CDEF (or some other
>rrdgraph magic) so that if the current plot point contains no data,
>it looks ahead into the RRD file and uses that data?

Lets clarify what you mean/want ...

Firstly, if we assume you are sampling at midnight, 6am, midday, and
6pm, and you are graphing at 3pm - what do you get ? what do you want

If you are getting a graph that shows some data at midnight, 6am, and
midday - but gaps in between, then that's a matter of adjusting your
rrd to allow for the sampling you are doing.

If your graph shows blocks from midnight to 6am, 6am to midday, but
you want something drawn from midday to 3pm - then you can't have it
as the period midday to 6pm has not happened yet and so cannot be

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