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

[Mark Easton]

Thanks Tobi - that is perfect. And I am sorry that I am the 1000thst person
to ask this queston! :) 

> -----Original Message-----
> From: Tobias Oetiker [mailto:tobi at oetiker.ch] 
> Sent: Wednesday, November 19, 2008 9:44 AM
> To: Mark Easton
> Cc: rrd-users at lists.oetiker.ch
> Subject: RE: [rrd-users] How Does RRDTool Produce Chart with 
> MANY Data Points
> 
> Tomorrow Mark Easton wrote:
> 
> > 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.
> 
> Mark,
> 
> I think I have understood you perfectly (you are only about 
> to 1000thst person to ask this question). But I guess I have 
> still not reached the point where I am able to explain this 
> to people so that they understand in the first round ...
> 
> If you plit 10'000 points to a chart 1000 pixel wide, then 
> rrdtool does NOT plot every point, but it takes groups of 10 
> points and figures out where to draw the pixel in the graph. 
> The method it uses for this process it the same that was 
> asigned to the RRA unless you add a reduce optino to the DEF 
> line when pulling the data in.
> 
> Since you did not add a reduce option you see the average of 
> 10 point plotted.
> 
> For performance reasons it makes sense to have additional 
> RRAs roughly matching the graph resolutions people will be looking at.
> 
> hope this helps
> tobi
> 
> 
> if you like, I can repeat for you what I wrote yesterday.
> >
> > 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
> > > 9902 / sb: -9900 No virus found in this incoming message.
> > > Checked by AVG - http://www.avg.com
> > > Version: 8.0.175 / Virus Database: 270.9.4/1795 - Release
> > > Date: 11/17/2008 5:24 PM
> > >
> >
> >
> 
> --
> Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, 
> Switzerland http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 
> 9902 / sb: -9900 No virus found in this incoming message.
> Checked by AVG - http://www.avg.com
> Version: 8.0.175 / Virus Database: 270.9.6/1797 - Release 
> Date: 11/18/2008 11:23 AM
>