[rrd-users] Save and Calculate Percentil

[Rafal Gwizdala]

Oops, I think I didn't really understand your question...
The answer should be: store your percentiles separately (in separate DS-es)
and choose the aggregation function that makes most sense in your case, for
example the average.


On Sun, Aug 17, 2014 at 8:19 PM, Rafal Gwizdala <rafal.gwizdala at gmail.com>
wrote:

> There's no 'percentile' consolidation function and it can't be derived
> from other statistical functions available in rrdtool, so i think it would
> be better to calculate the percentiles before storing them in RRD.
> This would of course require storing the data for extended periods of
> time, and to calculate 24h percentile you'd have to store 24 h worth of
> samples, which could be difficult.
> Here's a link to some approximate method which doesn't require you to
> store all samples because it's based on histograms. And histograms are an
> 'additive' measure, so you can add 24 hourly histograms together to
> calculate a daily percentile.
> http://techblog.molindo.at/2009/11/efficiently-tracking-response-time-percentiles.html
>
> I'm also doing some percentile calculations for app performance data, but
> I'm using a different approach: a fixed time window of 5 minutes and I
> calculate multiple measures for that period: average, median, 95th, 98th
> and 99th percentile. These measures are then writtend to a RRD file every
> minute.
>
>
>
> On Sun, Aug 17, 2014 at 6:57 PM, Peter <pspiegler at gmx.de> wrote:
>
>> Hi,
>> 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
>> function.
>> 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% ).
>>
>>
>> Peter
>>
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>> --
>> View this message in context:
>> http://rrd-mailinglists.937164.n2.nabble.com/Save-and-Calculate-Percentil-tp7582357.html
>> Sent from the RRDtool Users Mailinglist mailing list archive at
>> Nabble.com.
>>
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>
>
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