[rrd-users] Save and Calculate Percentil

Peter pspiegler at gmx.de
Sun Aug 17 18:57:58 CEST 2014

I use rrdtool to store measurement data in rrd files used by Cacti.
The measurement data have an interval of 50 ms. 
I need Average, Max, 99% and 5% Percentil.
I used the lowest possible step size in the rrd files:1 second.
For Average &  Max I created separate rrd files with RRAs:
1s: for a week , 1 min: for a month , 5 min: for a year
My program now calculate every second the max & avg values and updates the
rrd files.
This works fine, also in Cacti.

Is a solution possible for the percentiles?
The prefered solution would be: based on the 50 ms data.
But a 50 ms step size is not possible. 

And percentiles of small intervals are not so interesting.
I could calculate the percentiles in my program for intervals 
5/10/15/30/60 min, 3/6/12/24 hours 

But how should I define the rrd file and update the rra for this intervals?
Now the RRA are calculated from rrdupdate by the given consolidation
Or can I set each RRA manually?

And Cacti need also a consolition function to create a DEF for rrdgraph  ,
i.e. for MAX
DEF:a="/Data/rrd/DataMax.rrd":"DATAMAX":MAX \
Which RRA use rrdgraph (called by Cacti)?
If rrdgraph use always the  RRA with the smallest matching intervall, so I
can use LAST or MAX (for 99%), MIN (for 5% ).


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