[rrd-users] Percentile consolidation

[Steve Shipway]

Percentiles cannot be calculated incrementally; you need the entire dataset to deduce them whereas mean, max, min only require the last calculation result and possibly the number of samples so far.  Hence you cannot have the percentile as a CF

However the RRDTool RPN functions include a percentile calculator, so you can still deduce this on the fly as you graph using the available samples.  You would need to be careful to ensure that the data series over which you are aggregating is of maximum granularity though if you want to ensure maximum accuracy

Steve

Steve Shipway
University of Auckland ITS
UNIX Systems Design Lead
s.shipway at auckland.ac.nz<mailto:s.shipway at auckland.ac.nz>
Ph: +64 9 373 7599 ext 86487

________________________________
From: rrd-users [rrd-users-bounces+s.shipway=auckland.ac.nz at lists.oetiker.ch] on behalf of Pablo Chacin [pchacin at sensefields.com]
Sent: Saturday, 24 October 2015 11:43 p.m.
To: rrd-users at lists.oetiker.ch
Subject: [rrd-users] Percentile consolidation

Greetings

Been able to pre-calculate an store certain data percentiles, like media an 95 percentile is a common requirement for any metrics database, as these aggregation functions are much more stable and representative of data than the average or maximun values.

I saw that the mean was recently included as an consolidation function in rrdtool, but still there's no possible to calculate other arbitrary percentiles. Interestingly, percentiles have been available when retrieving data for graphs or reporting.

Is there any compiling reason not to include percentiles as consolidation functions? Is there any plan to do so in the future?

Regards


---------------------------
Pablo Chacin
CTO
SenseFields SL
Tlf (+34) 93 250 45 98
Gran Via 674, principal 1º
08010 Barcelona, Spain
http://www.sensefields.com<http://www.sensefields.com/>


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