[rrd-users] RRDTool Fetch : Recover data with a different resolution of the RRA

[Ryan Kubica]

rrdtool will provide a 'consolidation on the fly' but not with fetch, only with xport.

use xport just like you would to create a graph (with the graph calls changing to XPORT instead of things like LINE, AREA, etc), and set the width ( max rows ) -- option -m to the number of rows you need between start and end.  You will need to calculate this, but that's easy enough: (( end - start ) / step))

rrdtool does have the mildly annoying feature of wanting to return 10 rows though, so be aware of that when coding your functions and take it into account.


From the docs for rrd xport:
-m|--maxrows rows (default 400 rows)
This works like the -w|--width parameter of rrdgraph. In fact it is exactly the same, but the parameter was renamed to describe its purpose in this module. See rrdgraph documentation for details.




________________________________
From: Steve Shipway <s.shipway at auckland.ac.nz>
To: LE GONIDEC Romain <romain.le-gonidec at cg27.fr>; "'rrd-users at lists.oetiker.ch'" <rrd-users at lists.oetiker.ch>
Sent: Saturday, September 24, 2011 1:03 PM
Subject: Re: [rrd-users] RRDTool Fetch : Recover data with a different resolution of the RRA

RRDTool does not create a consolidation 'on the fly'.  Therefore, if you need a particular average, you need ot add an RRA.

Why is this?

Because, RRDTool is optimised for rolling up averages.  As averages are consolidated, data is lost, so it is quite likely that you cannot mathematically determine an average over a different resolution.  Also, the colsolidation is the 'expensive' part, so by doing this progressivly as theupdates come in the performance is improved.

You specify a resolution in the FECTH or GRAPH because there may be more than one possible resolution at the requested time interval, if you have multiple RRAs that cover it.  If an exact match is not available, RRDTool will use the closest available match.

Hope this helps,

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 LE GONIDEC Romain [romain.le-gonidec at cg27.fr]
Sent: Friday, 23 September 2011 2:47 a.m.
To: 'rrd-users at lists.oetiker.ch'
Subject: Re: [rrd-users] RRDTool Fetch : Recover data with a    different       resolution of the RRA

I am therefore obliged to add an RRA?
RRDtool can not calculate your own?
Why then specify a resolution. Only suffient timestamp.

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