[rrd-users] Graphing Sparse Data

Simon Hobson linux at thehobsons.co.uk
Wed May 14 17:19:00 CEST 2008

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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