[rrd-users] Can't understand rrd way of storing data

[Benoit Giannangeli]

Hi,

I've just discovered rrd and it seems to be the perfect tool for
collecting statistical data. Anyway I don't really get how rrd does to
collect data.
I just want to get exact values at exact times.

Here is an example:

rrdtool create test.rrd --start 1217401440 --step 20
                        DS:messages:GAUGE:40:U:U
			DS:processed:GAUGE:40:U:U
			DS:msize:GAUGE:40:U:U
			RRA:AVERAGE:0.99:1:6

rrdtool update test.rrd 1217401462:5.0:U:U
rrdtool update test.rrd 1217401463:5.0:U:U
rrdtool update test.rrd 1217401470:7.0:U:U
rrdtool update test.rrd 1217401471:3.0:U:U
rrdtool update test.rrd 1217401490:1.0:1.0:4181320.0  # Got 4181320.0
at time 1217401490 so why is it stored at 1217401480 ?
rrdtool update test.rrd 1217401496:2.0:U:U
rrdtool update test.rrd 1217401497:8.0:U:U
rrdtool update test.rrd 1217401535:1.0:1.0:1.3855684E7
rrdtool update test.rrd 1217401548:1.0:1.0:4181310.0
rrdtool update test.rrd 1217401560:1.0:1.0:1457203.0
rrdtool update test.rrd 1217401562:4.0:U:U
rrdtool update test.rrd 1217401563:6.0:U:U

rrdtool fetch test.rrd AVERAGE --start 1217401420 --end 1217401560

1217401440:  NaN  NaN  NaN
1217401460:  +5.0000000000E00  NaN  NaN	  # I got nothing within
1217401440 and 1217401460, so why 5 is stored ?
1217401480:  +3.8000000000E00  +1.0000000000E00  +4.1813200000E06
1217401500:  +1.3250000000E00  +1.0000000000E00  +1.0924058545E07
1217401520:  +1.3250000000E00  +1.0000000000E00  +1.0924058545E07
1217401540:  +1.0000000000E00  +1.0000000000E00  +1.1437090500E07
1217401560:  +1.0000000000E00  +1.0000000000E00  +2.5468458000E06
1217401580:  NaN  NaN  NaN

I don't understand why I get values such as 1.3 for messages or
2.54E06 for msize...

Anyway, why is it so hard to store value as they are ?

-- 
Benoit Giannangeli

http://www.giann.fr