[rrd-users] Re: Having problems with rrd graphs... help please

[Fernando Nieto]

Hello Alex and everybody, 

I've been using MRTG + RRDtool for more than 3 years, and later I have
developed some applications using RRDtool. It has been one month ago when
I've been awared of some behaviour I can't understand. I see you have a deep
knowlegde about rrdtool behaviour as you has made several contributions. I
trust you can help me to clarify my mind.

I'm polling for data from external sources and storing it into rrds every 5
minutes. I have GAUGE DS's and one AVERAGE RRA with steps=1. When I update
the rrd database I always force the timestamp to the last step multiple
(maybe the perl code it's clearer: $now=time(); $ts=$now-$now%$STEP).

Then if I receive the values 1,3,1,5,1 for one DS at t0, t1, t2, t3... my
rrd will store exactly those values:

             AVERAGE RRA  	MAX RRA
	10:00  	1		  1
	10:05  	3		  3
	10:10  	1		  1
	10:15  	5		  5
	10:20  	1 		  1

and these are also the values I get when I use rrdtool fetch. With steps=1,
the RRA will store exactly the same values even if I use AVERAGE, MAX, MIN
or LAST.

When I graph these data I think I should see the same info as when I fetch
it, even if my graph is 400x100 or 600x200. 

You have told me this behaviour makes sense, I'd like to know how RRDtool
works in order to calculate the graph output, and how graph dimesions or
x-axis time range can affect to its calculation. Could you help with this?
Any reference will be welcome.

Thanks so much. 
Fernando 


> -----Mensaje original-----
> De: rrd-users-bounce at list.ee.ethz.ch 
> [mailto:rrd-users-bounce at list.ee.ethz.ch] En nombre de Alex 
> van den Bogaerdt
> Enviado el: jueves, 06 de mayo de 2004 9:40
> Para: rrd-users at list.ee.ethz.ch
> Asunto: [rrd-users] Re: Having problems with rrd graphs... help please
> 
> On Thu, May 06, 2004 at 09:26:27AM +0200, Fernando Nieto wrote:
> 
> > Please check the images i'm sending, both are completely 
> > equivalent, that is, the same rrd, the same time span... the only 
> > difference is the graph height and width. I expected to get the same
> > graph but, as you can see, they are difference, both the graph and 
> > the legend values. Could somebody tell me if that's possible to happen 
> > and why?
> 
> 500 pixels or 600 pixels, that means the time span per 
> interval is different.  A different time span per interval 
> _may_ mean a different RRA is selected.
> 
> Just calculate what RRDtool would do.  I think it makes sense.
> 
> Alex
> --
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