[collectd] Hit counter in threshold

[Peter Bray]

Hi,

>  1) hysteresis, i. e. something like this:
>     -- 8< --
>       if (value > (threshold + epsilon))
>         status = bad
>       else if (value < (threshold - epsilon))
>         status = good
>       return status
>     -- >8 --
>     This, used right, should provide modest flapping protection.

Just a small comment, hysteresis as used in the satellite control 
systems I've worked with over the last eight years, means N samples 
above/below a threshold to trigger the condition. So for example: if RH 
(Red High) >= 10.0 with hysteresis of 3, then you require at least three 
samples at or above 10.0 to trigger a red high alarm. This also seems to 
match the definition in the MacOSX Desktop Dictionary "the phenomenon in 
which the value of a physical property lags behind changes in the effect 
causing it". And yes we used this a flapping protection on noisy data 
from the satellites (Solar Wing Position Potentiometers come to mind, 
where we could experience HUGE 1 sample spikes in the data)

Others may have a different understanding of hysteresis but I thought I 
mention this understanding as naming is so important to understanding.

Regards,
Peter