[rrd-users] Re: Fw: rrd 1.2.15 stores UNKNOWN as zero

Tobias Oetiker tobi at oetiker.ch
Sun Aug 13 17:53:12 MEST 2006

Hi Wilfred,

I looked at your report again, the 'problem' you see is that you
are skimming a border case ... rrdtool does handle subsecond
resolution for updates (and N is a subsecond timestamp), but if
this does get mixed with unknown data, then rrdtool can not
'remember' subsecond unknown resolution. This means that only
partially known seconds get to be fully known seconds in the final
analysis ... this again leads to lower values for border cases ...
check out my demo:


$R create unknown-0-1.rrd   \
            --step 10 \
            --start 1000000000 \
            DS:DS1:GAUGE:30:0:100   \
            RRA:AVERAGE:0.5:1:5 \

$R updatev unknown-0-1.rrd 1000000005:15
$R updatev unknown-0-1.rrd 1000000011.1:U
$R updatev unknown-0-1.rrd 1000000016.9:U
$R updatev unknown-0-1.rrd 1000000021.1:15

return_value = 0
return_value = 0
[1000000010]RRA[AVERAGE][1]DS[DS1] = 1.5000000000e+01
return_value = 0
return_value = 0
[1000000020]RRA[AVERAGE][1]DS[DS1] = 1.1625003750e+01

for the first step we know only half the seconds (5) but they are
all known so we get 15 as a result

for the second step we know 3.1 seconds (16.9 to 20) so here the
average should be 15 as wel. but since unknown seconds get rounded
down, we get

  15*3.1/4 = 11.6

hope this helps
Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten
http://tobi.oetiker.ch tobi at oetiker.ch ++41 62 213 9907

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