[rrd-users] How Does RRDTool Produce Chart with MANY Data Points

[Mark Easton]

Hi Tobi,

I think you have missed my point.  Please ignore the ave, max, min stuff I
spouted on about (I edited my post online).

The RRA I am using in my graph has no consolidation. It presents for one
month, about 40,000 points (60 second readings from my sensor - my step is
60). ie

RRA:AVERAGE:0.5:1:40320   (I assume that AVERAGE, MAX, MIN of 1 value will
all be the same??)

My question is that when I ask RRDTool to produce a graph for this does it
just plot all 40320 points or does it do some optimisations based on the
size of the graphic being produced? For 12 months, it would need to plot
524,000 odd points.

Cheers,
Mark

> -----Original Message-----
> From: Tobias Oetiker [mailto:tobi at oetiker.ch] 
> Sent: Tuesday, November 18, 2008 7:53 PM
> To: Robert Easton
> Cc: rrd-users at lists.oetiker.ch
> Subject: Re: [rrd-users] How Does RRDTool Produce Chart with 
> MANY Data Points
> 
> Hi Robert,
> 
> Yesterday Robert Easton wrote:
> 
> >
> > Hi,
> >
> > If I ask RRDTool to plot a chart with 10,000 data points it does so 
> > very fast. What is RRDTool doing in the code? It appears to 
> me that it 
> > is averaging or smoothing the data. Is that right?
> >
> > I was actually plotting readings from a temperature sensor 
> taken every 
> > minute for one week. So that is 60 x 24 x 7 = 10080 data 
> points. In a 
> > patrticular day the temperature might have a min of 8 and a 
> max of 24, 
> > but the resulting chart did not manage to show that min and 
> that max 
> > in a particular day.
> >
> > So what does it do?
> 
> rrdtool uses the same consolidation function that was defined 
> in the RRA to further consolidate the data so that it matches 
> the resoltion of the graph ... if you want to see min and 
> max, setup additional rras with MIN and MAX consolidation functions
> 
> OR
> 
> use the reduce option in the DEF line to override the reduce 
> function with MIN or MAX respectively.
> 
> cheers
> tobi
> 
> >
> > Thanks,
> > Mark
> >
> 
> --
> Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, 
> Switzerland http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 
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