[rrd-users] Re: MIN and MAX work as designed and there are good reasons for

[Cristian Ghezzi]

It really has to do with the nature of the data you are monitoring.

I'm monitoring the response time of some COBOL programs that run on a 
mainframe and are called from an internet application.
For every call made to some program, I can compute the response time.
I know exactly how many calls are made, when they are made, and how many 
milliseconds each lasts.
I want to plot a graph that shows how quick the programs run when the 
application is online.
A good graph is one that shows the maximum response time in the last 10 
seconds, so that I could see if some of the programs gets stuck or is 
unusually slow.
In order to do this, I collect data for 10 seconds, keep the maximum 
value, and feed it to a rrdtool GAUGE.
The value I store in the database IS the maximum value within the 10 
seconds, as I have the knowledge of all the data-values at any point in 
time.
I was expecting to be able to feed the computed value to rrdtool at any 
point in the step, but I was getting incorrect results which led to my 
first email.
Now I just feed the values step-aligned, and everything is fine.

Don't you think my case could be better handled by the tool?


Thank you for your answer

Cristian



Tobias Oetiker wrote:

> Cristian,
>
> the reason for MIN and MAX only recording the 're-binned' values is
> that anything else is pure randomnes, assuming your queries are not
> 100% equidistant ... this especially so with counters. For gauge
> datasources min and max are illusions anyway, as you are
> reading the data at some  point in time and have no knowledge of the
> data-values at any other  point ...
>
> so your quest should not be trying to change the way min/max
> behave, but rather understanding why it works the
> way it works ...
>
> cheers
> tobi
>
>  
>

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