[rrd-users] 95th percentile per day,week,or month

[Steve Shipway]

I don't believe this is currently possible in a single pass, though it is a rather interesting idea...

The 'percent' RPN function, which calculates percentiles, is only available in a VDEF and so works on the entire visible dataset to give a single value.  You will also have the issue that you would need to extend the underlying RRAs to provide data at the best possible resolution for the entire graph width.  If you try to calculate a percentile using the 1-day granularity RRAs then you'll get artificially flattened values.

You could manage it by adding an additional manual calculation.

Create a new RRD file to hold the percentiles this should have 'last' RRAs, and a very large heartbeat and step (1 month for the step so as not to average, and with 'LAST' type RRAs so you can update it daily).  Run a periodic job (daily or monthly) to calculate the 95th percentile from the main RRD for the last calendar month, and store the value into the new RRD.

Then you can graph over both RRDs with the new one providing the 95th percentile lines.

Until RRDTool provides a percentile type CF for RRAs, or a percentile RPN function allowing a time window to be specified,  this is the best you can do.  Maybe we can ask for these new features in RRDTool 2.x :)

Steve

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


________________________________________
From: rrd-users-bounces+s.shipway=auckland.ac.nz at lists.oetiker.ch [rrd-users-bounces+s.shipway=auckland.ac.nz at lists.oetiker.ch] on behalf of KENNETH D MILLER II [kdm193 at psu.edu]
Sent: Thursday, 31 January 2013 10:30 a.m.
To: rrd-users at lists.oetiker.ch
Subject: [rrd-users] 95th percentile per day,week,or month

Is there a way to graph a 95th percentile per day, week or month?  If I create a yearly interface graph, can i draw a flat line for each month's 95th percentile instead of one for the whole timespan?  I have added a modified png as an example here:
http://www.personal.psu.edu/kdm193/rrdtool/95thgraph.png


Thanks,
Ken

Systems Design Specialist
Network Development Engineering
Penn State University


Co-Chair Internet2 Performance Working Group
SuperComputing SCinet Measurement Team Member

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