[rrd-users] Re: Graph data is affected by the size of PNG image

[Alejandro Galue]

Hello Simon,
Thanks for your quick response.

I follow your suggestions. Initially, the start and end steps was:

Tue Nov  1 00:00:00 2006
Tue Dec  5 00:00:00 2006

I changed to:

Tue Nov  1 00:05:00 2006
Tue Dec  5 00:05:00 2006

and put on both DEF:

reduce=MAX:step=300

Now, the small graphs looks much better, but steel shows some differences.

The small one shows some peaks now showed on bigone, and viceversa.

I included on my last response on the list the RRD and the script file. 
This file is about 400K aprox. Please tell me if you need it.

Thanks again, and best regards,

Alejandro Galue.

Simon Hobson wrote:
> Alejandro Galue wrote:
> 
>> Graph 1
>> http://lists.ee.ethz.ch/p/03-g1.png
>>
>> Graph 2
>> http://lists.ee.ethz.ch/p/03-g2.png
>>
>> The real data is showed on "Graph 2" (the big one); but "Graph 1" (the
>> small one) shows non valid data.
>>
>> If you see Graph 1, almost all peaks dissapears from graph.
>>
>> I used "reduce=MAX" on DEF lines but this does not work.
> 
> Graph 1 looks very much like the data from graph 2 reduced to a lower 
> resolution by an averaging function. Chances are that the start & end 
> times for your graphs are causing the RRD tool to select a different 
> set of data from your archive than you were expecting.
> 
> It is a good idea to select your end time as a multiple of the step 
> size for the resolution of the data you want to plot, as in end = end 
> - ( end % step ). Then select your start time as the end time minus 
> the step size times the number of pixels (or should that be "number 
> of pixels - 1" ?).
> 
> 
> If you want to show max values on a graph then you must have a max 
> value aggregation in your rrd. It is impossible to infer the max 
> values from an average !
> 
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-- Attached file removed by Ecartis and put at URL below --
-- Type: image/png
-- Size: 79k (81911 bytes)
-- URL : http://lists.ee.ethz.ch/p/graph-big.png


-- Attached file removed by Ecartis and put at URL below --
-- Type: image/png
-- Size: 44k (45317 bytes)
-- URL : http://lists.ee.ethz.ch/p/graph-small.png


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