[rrd-users] bug - no way to retrieve an RRA that is a multiple of another

[Jo Rhett]

So I'm looking at the fetch algorhithm for determining the RRA to  
use, and it appears that selection of an RRA that is a multiple of  
another is impossible unless you expand the time range to a period  
where both don't have data.

Example:

RRA - 5 minute average, 30,000 entries
RRA - 30 minute average, 3,000 entries
RRA - 2 hour average, 300 entries

So let's say that I want to get the 30 minute average for yesterday  
noon to today noon only:

All three of the following queries return the exact same result (5  
minute average)

rrdtool fetch datafile.rrd AVERAGE ds0 -s end-1d -e 12:00 -r 300
rrdtool fetch datafile.rrd AVERAGE ds0 -s end-1d -e 12:00 -r 1800
rrdtool fetch datafile.rrd AVERAGE ds0 -s end-1d -e 12:00 -r 7200

Dropping the "-r" or using an off time naturally returns the 1-minute  
values for the same period.

Obviously I could get the 5-minute average if I wanted it by using -e  
12:05 but there's no 30 minute average that isn't also a 5 minute  
average.

-- 
Jo Rhett
senior geek
Silicon Valley Colocation

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