[rrd-users] rrdtool fetch: problems with resolution (returned data doesn't match param)

[manuel aldana]

hi,

I want to fetch data from rrd in several time resolution steps. I 
followed http://oss.oetiker.ch/rrdtool/doc/rrdfetch.en.html.

But it doesn't give back data in the precision I request (either 600 or 
900 seconds). It simply gives back 5 minutes increments. If I set 1200 
sec as precision it the suddenly jumps to 30 minutes (1800 sec).

I am sure I misunderstand something about the --resolution parameter.

fetch script:
===
# static base time for easier testing/play-around
TIME=1299093300
  RRDRES=900

rrdtool fetch 
/var/lib/munin/localdomain/localhost.localdomain-cpu-idle-d.rrd AVERAGE 
-r $RRDRES -e $(($TIME/$RRDRES*$RRDRES)) -s e-2h | awk '{print $0;print 
strftime("%Y/%m/%d-%H:%M",$1)}'


returned data (get 5 minute increments instead of 900 sec = 15 minutes):
===
2011/03/02-18:20
1299086700: -nan
2011/03/02-18:25
1299087000: -nan
2011/03/02-18:30
....
2011/03/02-20:05
1299093000: 1.9164289439e+02
2011/03/02-20:10
1299093300: 1.8967866452e+02
2011/03/02-20:15
1299093600: -nan
2011/03/02-20:20

What is the right way to get the right resolutions back? I am using 
rrdtool 1.3.8.

-- 
  manuel aldana
  aldana at gmx.de
  software-engineering blog: http://www.aldana-online.de