[xymon] Graphing issue with data that only changes once every 24 hours

[Henrik Størner]

In <AANLkTi=OXLO7cVThaCK8vmZNNaumTGXfwTf+oPxuhqAh at mail.gmail.com> Phil Meech <pmeech at gmail.com> writes:

>These figures are currently sent in MB (I need to write a percentile
>calculation), but only once every 24 hours.  This all falls over when
>it comes to trying to graph the data in Xymon as it is not a constant
>feed of data every 300 seconds like other tests.  From the rrdtool
>documentation it seems like the data I am presenting is unsuitable for
>graphing in the normal method.  I've tried just about every data type
>and I only get a line drawn when data is received (else the graph
>drops out on every step without data).

When the RRD file gets created, one of the parameters is how often 
updates should be expected (it's called the "step" value). Xymon
uses 300 seconds for this value. Another parameter is the "heartbeat"
setting, which is the maximum time allowed between updates - if 
updates do not arrive within "heartbeat" seconds, then RRD won't 
show a graph because it believes the data is too sparse to make sense.
Xymon uses a value of 600 seconds for the heartbeat (allowing us to
miss one update and still keep the graph).

All of these settings are fixed when the RRD file is created. So what 
you need to do is re-create the RRD file with settings appropriate
for your data. Something like this would probably work:

rrdtool create mydata.rrd \
	--step 86400 \
	DS:mbytes:GAUGE:192800:0:U \
	RRA:AVERAGE:0.5:1:730

This create an RRD file where updates are expected once a day
(86400 seconds = 24 hours). There is one set of data in it,
called "mbytes" - this is a GAUGE, and it is minimum 0 and
has no upper limit ("U" = undefined). There is only one RRA archive
which holds 730 data-points, so you have room for two years of
data.

You can use "rrdtool info" on your current rrd file to see what
it looks like, in case you are not sure of some of these settings.

Once the RRD file exists, Xymon shouldn't have any problems 
with performing the updates or building graphs.


Regards,
Henrik