[rrd-users] Question about averaging daily ; but with 5 min. steps

Jean-Yves Avenard jyavenard at gmail.com
Tue Dec 15 13:49:47 CET 2009


2009/12/15 Simon Hobson <linux at thehobsons.co.uk>:
> Actually, the problem is VERY different from the usual
> multiply/divide by some value to get 'real' units.

YES !!
FINALLY !!!!!!!!!

> The problem is about doing a calculation that MUST be done on a 5
> minute sample period, in a graph where the resolution is 1day
> (86400). The calculation is such that doing the same sums over
> anything but a 5 minute sample period does NOT produce the right
> answer.


It's exactly what you said

I was going insane for a moment ; asking a question and being told
something entirely irrelevant and along the line "this is not the
right question".

> That is the danger of reading the first few lines and thinking it's
> the same question we've seen many times before.

Yes, it is indeed.

> Back to the question, if it's just a matter of getting the right
> value to print in the legend, then one route (I think) would be to do
> two runs through rrdtool. The first would generate no graph, just do
> the calculations at a resolution of 5 mins and output the answers.
> The values can then be included in the script that generates the
> graph on a second run.

That sounds like the simplest way... I had hoped to achieve the same
from within an RRD RPN expression. I almost achieved it but I guess
RRD is missing some key RPN commands, in particular modify values of a
previous run...

I guess the 1st run would feed data in a temporary RRD file, and the
2nd would work from it ... or is there a way for RRD to be fed all
data on the command line directly?

Because performance-wise, running a cron at 5 minutes interval will do
the job and it will be much fast to graph...

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