[rrd-users] rrdtool doesn't detect integer overflow

[Alex van den Bogaerdt]

On Wed, Aug 22, 2007 at 04:10:55PM +0400, Oleg Derevenetz wrote:

> Aha, so updating with value U at T-1 will not cause wrap when updating with value 0 at T. Really I guess something like that. 


The rate is calculated like this:

       delta(value)   CurrentValue - PreviousValue
rate = ------------ = ----------------------------
       delta(time)     CurrentTime - PreviousTime

For viewers still not using a fixed width font:

Rate equals delta(value) divided by delta(time)
which equals (CurrentValue-PreviousValue) divided by
(CurrentTime-PreviousTime).


If "PreviousValue" is unknown, then so is "CurrentValue - PreviousValue".
If this number is unknown, then dividing it by 1 (one second) also
results in unknown.  The rate is thus unknown, not a huge number
which you currently suffer from.

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