[rrd-users] How Does RRDTool Produce Chart with MANY Data Points
tobi at oetiker.ch
Tue Nov 18 07:52:45 CET 2008
Yesterday Robert Easton wrote:
> 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
use the reduce option in the DEF line to override the reduce
function with MIN or MAX respectively.
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
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