[rrd-users] How to get MAX/MIN of non-rates?

Tony Mountifield tony at mountifield.org
Tue Apr 2 16:06:18 CEST 2013

In article <kj5777$r4h$1 at softins.clara.co.uk>,
Tony Mountifield <tony at mountifield.org> wrote:
> In article <37C388565C9E4EC88E23BAA2021C1435 at DESK>,
> Alex van den Bogaerdt <alex at vandenbogaerdt.nl> wrote:
> > > Now, because the value was 5 for a fifth of the period, the average value
> > > stored is 1, which is fine. However, the MAX table also has a value 1 
> > > stored,
> > > instead of the value 5 that I expected.
> > >
> > > It appears the CF for MAX doesn't apply to values within a period, but 
> > > only
> > > when periods are consolidated into longer periods.
> > 
> > > I write values with their timestamps as and when they change, and had 
> > > expected
> > > RRD to keep the highest value written within the period as the stored MAX
> > > value for the period.
> > 
> > You could set step equal to 1 (i.e. one second) and then consolidate 300 of 
> > those steps in your first RRA, the one with the lowest number of seconds per 
> > bucket.
> > 
> > In other words: instead of step==300 and steps_per_CDP==1, you set step==1 
> > and steps_per_CDP==300.
> > 
> > Please try and get back.
> Interesting! I hadn't thought of that. It sounds promising - thanks!
> I'll let you know how I get on - although it won't be until next week.

I've just tried it in a test setup, and it works perfectly. Of course,
I also needed to scale up the steps per CDP by 300 for the longer-term
RRAs in the file too.

I tried both with and without an additional RRA with steps_per_CDP of 1,
to see if it made any difference, but it works fine without, which is great.

Thanks for the idea.

One question, just out of interest: when an RRD file is defined with multiple
RRAs of different resolutions and time durations, are the lower-resolution
RRAs calculated using the data from the higher-resolution ones, or are all
of them calculated independently, from just the input values as they arrive?

Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org

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