[rrd-users] Re: problem

Stephan Harren sh at abovenet.de
Wed Sep 3 15:38:02 MEST 2003

> I created an RRA
> rrdtool create test.rrd -s 5 \
> DS:getal:GAUGE:60:U:U \
> RRA:LAST:0.5:1:50 \
> RRA:LAST:0.5:2:20

Did you insert this values with or without timestamp? The point is, that your 
rrd accepts one value every 5 seconds, and one value gets unknown, if you 
don't insert something for 60 seconds. As you see, the first value you 
inserted was 979 (just once). So every five seconds, it's 979 because there 
is no new value but the old one is valid, (because it has been inserted 
during the last 60 seconds).

As you see, taking care of step and heartbeat is very important. 607.8 comes 
from 4 times 515 plus 979 divided by 5, which means the last input that has 
been made was 979, but through the next 4 datapoints there was just 1 input 
made, which now becomes valid for calculation since then. Again the problem 
is the step/heartbeat ratio is the problem.


10 - 979
15 - No Input
20 - No Input
25 - No Input
30 - 515

leads to 

10 - 979
15 - 979
20 - 979
25 - 979

because at 25, 20, 15 there was no input, but there is a known and still valid 

30 - 6.087

Internally (not in the table, above of it, if you use rrdtool fetch) there is 
the last input at 10 still saved. Now there is a new input at 30. As they are 
both valid (because of heartbeat 60),there is a rate calculated which leads 
to this confusing result.

And so on ...

If you insert one value every five seconds with the exact timestamp, this 
won't happen, but if I was you, I would work on the step/heartbeat ratio. You 
can find a lot about this on the rrdtool homepage.

Hope this helps and did not lead to any further confusion. And by the way, I 
hope that I'm right .... ;-)) (Tobi, correct me if I'm wrong)

Best regards,

Stephan Harren
Manager Site Operations
Phone +49 69 90554 153
Fax +49 69 90554 111
Cell +49 173 7011126

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