[rrd-users] Re: Fetching data from RRA's

[Tobias Oetiker]

Today you sent me mail regarding Re: [rrd-users] Fetching data from RRA's:

*> > 
*> > Since every data point is based on 7200 seconds (2 hours) worth of data.
*> > However, I keep getting the data for the 24 hour RRA. Am I
*> > misunderstanding something?  I did a dump and the data is definitely
*> > there.
*> >   
*> After some keywords from Tobi, I did some testing on this.
*> 
*> > 
*> > what fetch does it firsts selects the RRAs which cover the requested
*> > timespan and THEN selects the one with the requested resolution ... 
*> > 
*> 
*> It seems that this means that the start and end times should be
*> aligned onto exact sample-times. If not, there will be no exact match
*> for the desired RRA and it will select the first that contains the
*> entire requested time span.
*> 
*> So:
*> 
*> TIME=`date +%s`
*> rrdtool fetch some.rrd AVERAGE -r 3600 -e $TIME -s end-1d
*> 
*> is different from
*> 
*> TIME=`date +%s`
*> TIME=$((TIME/3600))
*> TIME=$((TIME*3600))
*> rrdtool fetch some.rrd AVERAGE -r 3600 -e $TIME -s end-1d
*> 
*> <test>
*> [user at home /u]$ rrdtool fetch x.rrd AVERAGE -r3600 -e924555600 -send-2h|wc -l
*>       5
*> [user at home /u]$ rrdtool fetch x.rrd AVERAGE -r3600 -e924555601 -send-2h|wc -l
*>      28
*> </test>
*> 
*> The second line (only a different end-time, by one second...) gives data
*> from another RRA. My guess is that the above assumption is correct.
*> If so, this is not clear from the manual (at least not for two inhabitants
*> of the global village) and it was not obvious to find out.

could it be, that the RRD you were looking at does start at 924555600 or
were these times chosen to be well inside the available data ?

cheers
tobi

*> 
*> Regards,
*> Alex
*> 

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