[rrd-users] VDEF MINIMUM

Oliver oliver341 at live.co.uk
Fri Aug 12 11:44:52 CEST 2011

Yes, but only by a tenth of a unit, but enough to make me investigate. When 
I did testing and found that it was possible for the last 10,000 seconds to 
have a much higher minimum than the last 15,000 seconds I lost confidence in 
the function and moved to fetch-ing and parsing.

The DEF is the same, DEF:noise=noise.rrd:noise:AVERAGE .

-----Original Message----- 
From: Alex van den Bogaerdt
Sent: Friday, August 12, 2011 9:59 AM
To: rrd-users at lists.oetiker.ch
Subject: Re: [rrd-users] VDEF MINIMUM

Are you saying that there is a discrepancy between what MIN and MAX
report, vs. what can be seen on the graph?

If so: are you sure you use the same (C)DEF to get min and max from?

> Hi Alex,
> Thanks for that, I'll study this some more.
> For now I'm doing it the "messy" way, i.e. fetch-ing all the data into an
> array, sorting it numerically ascending and then taking the first and last
> values of the array as minimum and maximum values plotted on the graph.
> As I say it's not as clean as using an rrdtool function directly to
> extract
> min/max, but it seems to give results which correlate exactly to the
> minimum
> and maximum points plotted on the graphs which is the main thing.
> Thanks,
> Oliver.
> -----Original Message-----
> From: Alex van den Bogaerdt
> Sent: Thursday, August 11, 2011 11:05 PM
> To: Oliver
> Cc: rrd-users at lists.oetiker.ch
> Subject: Re: [rrd-users] VDEF MINIMUM
> bottom paragraph of my reply, "... the other ..." is the relevant part
> then. You want to display a certain amount of RRA rows in less the amount
> of pixel columns, so RRDtool is going to do some on the fly consolidation.
> Try an end time which is n*60, try to display 400*60 seconds, do so in 400
> pixel columns.
> GPRINT last, min, average, max.
> Now try the same, except that you display 400*30 seconds.
> This part of the tool has had more than its fair share of problems in the
> past, I seem to recall an off by one error or two, and other problems.
> There could be differences between the various RRDtool versions, but all
> versions will have some form of on the fly consolidation, where multiple
> RRA rows will be combined into one pixel row.
> Once you understand the relatively easy n*30 vs. n*60 case, try to figure
> out what the tool does with n*40, n*50 and so on.
> GPRINTing the time component of the first and last sample on the graph may
> also be interesting.
> cheers,
> Alex 

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