[rrd-users] consolidation or no consolidation?
qzy at imind.hu
Mon Jul 16 14:42:17 CEST 2007
On Mon, 16 Jul 2007, Simon Hobson wrote:
> KOZMAN Balint wrote:
> >Well, on the presentation side (regarding rrdgraph) I can ensure, that
> >number of values to be presented will fit. To be more precise, I have a
> >worker thread somewhere which inserts recently collected data to the rrd
> >on a 10 sec period, having only 1 DS in the rrd. Now, when drawing a graph
> >of the last 1 minute of this DS, all I have is exactly 6 entries in the
> >rrd. Thus I'd like to see those values on the graph, and not something
> >that just compares to them somehow. Obviously when graphing a month-long
> >period, I would like to see consolidated data as that's the only thing I
> >can expect.
> >So what parameters should I use during rrd creation to get this? A small
> >example would help a lot.
> You need an rrd with a step size of 10 AND you must feed it data
> points with timestamps exactly divisible by 10 - about 10 s is not
> good enough, it has to be EXACTLY 10s. You need a consolidation
> function in the rrd with ONE step per consolidated step - is matters
> little which you use as min, avg, and max are the same for one single
> value.. If you then graph that rra with start and end times which are
> themselves exactly divisible by 10s AND number of pixels exactly
> equal to number of samples AND end time which is no later than last
> complete step time AND the start time is within the range stored by
> the hi-res rra THEN you should get exactly the same values out as you
> put in.
> What is happening if you meet all these requirements is that you will
> avoid normalisation (input data already matches database time slots)
> and avoid consolidation (or more technically perform null
> consolidation) by having a CF that is only one sample long.
Thanks for this great explanation, it really helped a lot!
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