[rrd-users] Re: Unbelievable fetch

[Alex van den Bogaerdt]

On Fri, Jul 28, 2006 at 12:26:04PM +0200, Olivier Doucet wrote:

> 1/ First, I create my graph with that :
> /usr/local/rrdtool/bin/rrdtool create test.rrd --step 300 --start 1154077200 
> DS:TotalAccesses:DERIVE:300:0:100000000000 RRA:AVERAGE:0.5:1:600 
> RRA:MAX:0.5:1:600

You have set the heartbeat to 300 seconds here.


> 2/ I import values on it :
> rrdtool update test.rrd --template TotalAccesses 1154077202:15543824 
> 1154077502:15559245 1154077802:15574243 1154078105:15591902 
> 1154078403:15609148 1154078702:15627641 1154079002:15645008

update at 1154077202
update at 1154077502, rate (15559245-15543824)/(1154077502-1154077202)
update at 1154077802, rate (15574243-15559245)/(1154077802-1154077502)
update at 1154078105, rate unknown
update at 1154078403, rate (15609148-15591902)/(1154078403-1154078105)
update at 1154078702, rate (15627641-15609148)/(1154078702-1154078403)
update at 1154079002, rate (15645008-15627641)/(1154079002-1154078702)

1154078105 - 1154077802 = 303.  This is more than 300 thus the rate is
unknown.

update at 1154078105 affects these intervals:

a) 1154077800 to 1154078100
b) 1154078100 to 1154078400

these intervals are also affected by other updates:

The update at 1154077802 also affects interval (a)
The update at 1154078403 also affects interval (b)

Interval (a) is built from:
    2/300 times rate (15574243-15559245)/(1154077802-1154077502)
  298/300 times rate unknown

  more than 0.5 is unknown, so the normalized rate is unknown

Interval (b) is built from:
    5/300 times rate unknown
  295/300 times rate (15609148-15591902)/(1154078403-1154078105)

  not more than 0.5 is unknown, so the normalized rate is not unknown

Outcome: (approximately) 57.8724832214

Manually deducted:
interval ending at 1154078100 has rate unknown
interval ending at 1154078400 has rate 57.8724832214

> 1154078100: nan
> 1154078400: 5.7872483221e+01

unknown is the same as 'nan'
57.8724832214 is (approximately) the same as 5.7872483221e+01

HTH
-- 
Alex van den Bogaerdt
http://www.vandenbogaerdt.nl/rrdtool/

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