Using last values for graph when not able to poll.

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Using last values for graph when not able to poll.

#1 Post by tapufd » Fri Aug 20, 2004 5:03 pm

MRTG has the option unknaszero = Log unknown data as zero instead of the default behaviour of repeating the last value seen. Be careful with this, often a flat line in the graph is much more obvious than a line at 0.

Cacti always uses this option: unknown data = zero . For Cpu-load is this interesting, but for volume-usage it seems for me more interesting that you can choose to let cacti use the last seen value. So if the server is temporarely inaccessible, the graph of the volume-usage doesn't has gaps.

Checked cacti, but couldn't find this option.

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#2 Post by pvd » Wed Oct 06, 2004 2:21 am

personally, having written a data gatherer that did just this by mistake, for remote disk space/useage, I would have spotted a disk with Zero size, but one that was 3G and not growing it just looked normal, until quota threw me off and I learnt to add up.

I can see where this might be useful, but it needs to be optional, In my world data is data and not measuring it should be "nothing" not the last known value.

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yes, sometimes messes up the things, sometimes is very usefu

#3 Post by totoforte » Tue Jan 25, 2005 9:38 am

here.. i have a optical fiber connection, with 10mbits/s metropolitan bandwidth, and only 512kbits/s outside the network bandwidth. so i want to generate graphs for the outside traffic, and i set a max value of 512kbits to remove the spikes. all is fine, but when someone transfers from the metropolitan are leaves holes in my graph.
in this situation i would like to set a repeat last value seen behaviour, is not hard to implement it.
if someone can give me some directions(variable, functions) to modify in order to alter the behaviour, i`ll appreciate that.

thank you

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Re: Using last values for graph when not able to poll.

#4 Post by zyndarius » Thu Sep 15, 2011 7:07 am

First of all, excuse me for reviving a very old topic, but:

Is there any information about this? The possibility of configuring cacti to graph the unknown data = last value seen?

I would greatly appreciate any kind of feedback related to this.

Thanks in advance.

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Re: Using last values for graph when not able to poll.

#5 Post by gandalf » Fri Sep 16, 2011 4:24 pm

We do not have plans to fake wrong values into rrd files, not even as an option.
RRDTool itself has no option to do so as well.
So I fear, that you will have to do this on your own

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Re: Using last values for graph when not able to poll.

#6 Post by TheWitness » Sat Oct 29, 2011 6:41 am

For things that 'might' be gappy, simply increase the heartbeat, and your problems will be solved.

Code: Select all

[email protected]:~# rrdtool tune
RRDtool 1.4.3  Copyright 1997-2009 by Tobias Oetiker <[email protected]>
               Compiled Mar 26 2011 03:16:40

Usage: rrdtool [options] command command_options
 * tune -  Modify some basic properties of an RRD

        rrdtool tune filename
                [--heartbeat|-h ds-name:heartbeat]
                [--data-source-type|-d ds-name:DST]
                [--data-source-rename|-r old-name:new-name]
                [--minimum|-i ds-name:min] [--maximum|-a ds-name:max]
                [--deltapos scale-value] [--deltaneg scale-value]
                [--failure-threshold integer]
                [--window-length integer]
                [--alpha adaptation-parameter]

                [--beta adaptation-parameter]
                [--gamma adaptation-parameter]
                [--gamma-deviation adaptation-parameter]
                [--aberrant-reset ds-name]

RRDtool is distributed under the Terms of the GNU General
Public License Version 2. (

For more information read the RRD manpages
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