[rrd-users] Simple DEF Arithmetic

Chris Mason chris at netnix.org
Tue Aug 6 17:20:09 CEST 2013

Hi Jonan,

But when looking at a year, you may have consolidated the individual
> numbers into larger buckets - where the max-values are kept.
> Lets just create an example where two values are "joined" (timeslot
> increased to contain 2 values) - so we reduce the buckets to 5.
> Most people have maybe 2 weeks of data with full resolution, and then
> consolidate this to larger buckets (from minutes to hours) - and then after
> a few months of them  - go up to some even larger buckets (hours to days).
> With the same max, we would then have:
> A2:    3  5   6  4  4
> B2:    6  8   4  3  1
> And our new max-array of the sum would be:
> AB2:  9 13 10 7 5
> Where the max-value is 13 - and not 12 as above.

I see what you are saying, but this would change the MAX of A2 and MAX of
B2 between different bucket sizes.
But, if A and B both return the same MAX value for a 1 year resolution and
a 1 month resolution graph then doesn't this imply they aren't being


1M MAX of A: 749.807 M
1Y MAX of A: 749.807 M

1M MAX of B: 1744.822 M
1Y MAX of B: 1744.822 M

I'm not sure what you want to accomplish.
> If you are trying to look on some bandwidth-numbers you should probably
> not use max anyway - as even a very short peak would offset your hole
> yearly-data.

I am measuring link utilisation and we graph MAX as opposed to AVERAGE as
this gives us more accurate information on peak utilisation. They are
generally very high capacity links which don't produce bursty graphs.

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