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 <[email protected]>
To: LE GONIDEC Romain <[email protected]>;
"'[email protected]'" <[email protected]>
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
[email protected]
Ph: +64 9 373 7599 ext 86487
________________________________________
From: [email protected]
[[email protected]] on behalf of LE
GONIDEC Romain [[email protected]]
Sent: Friday, 23 September 2011 2:47 a.m.
To: '[email protected]'
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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