[rrd-users] FetchData Doubt

Simon Hobson linux at thehobsons.co.uk
Thu Jun 23 09:16:20 CEST 2011

mini priyanka wrote:

>I have an RRD with following archieves
>RRA:AVERAGE:0.5:1:1440"; // 1 Day Data
>"RRA:AVERAGE:0.5:5:2016"; // 7 Day Data
>"RRA:AVERAGE:0.5:60:720";  // 1 Month Data
>When I fetchdata for recent timestamp i.e for last two weeks I get 
>large number of timesamples with data in it.
>But when i try to fetch data say for example from last month till 
>last week, everything is NaN.
>Can I decide from archive the data to be fetched?

You can specify the resolution you want to fetch :
>--resolution|-r resolution (default is the highest resolution)
>the interval you want the values to have (seconds per value). 
>rrdfetch will try to match your request, but it will return data 
>even if no absolute match is possible. NB. See note below.

But see the important note further down the page :
>In order to get RRDtool to fetch anything other than the finest 
>resolution RRA both the start and end time must be specified on 
>boundaries that are multiples of the desired resolution. ...

So it seems that if you don't get your start and end time spot on, 
you won't get the resolution you want. It further seems that if you 
do get it wrong, then it uses the highest resolution data even if 
that doesn't cover the period you asked for.
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
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