[rrd-users] Things not adding up

Jared Watkins jared at jaredwatkins.com
Tue Apr 5 19:57:40 CEST 2011

On 4/5/11 11:39 AM, "Simon Hobson" <linux at thehobsons.co.uk> wrote:

>Jared Watkins wrote:
>>I'm most interested in the max values for this data and if you add
>>up all the individual max values you get a value that's 120.15
>>greater than the total printed on the graph both visually and in the
>In general you cannot add max values. Consider this (contrived)
>scenario. You have four data sets, and get PDP values like this :
>  A  B  C  D
>10  0  0  0
>  0 10  0  0
>  0  0 10  0
>  0  0  0 10
>Now it's clear to see that at no time does the combined set of values
>exceed 10. Now lets consolidate those into one MAX CDP :

In this case I don't think your argument is relevant.  I'm only storing
in/out bits for a single device in each rrd file... so I wouldn't store a
sum across devices in any one rrd. The problem appears when I read all
these separate files for the aggregate graph. Also.. if you manually add
up the displayed average and current values they do agree with the printed
totals.. only the max values are coming out wrong. Also.. it's off by a
rather odd amount. 

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