hysteresis and returning from warning state

[Sam Tilders]

Has there ever been any discussion of hysteresis values?

That is where a service has passed a threshold where it is then in a warning 
state, but when it goes below that threshold it doesn't return to an ok state 
until it passes a second threshold.

For example, monitoring the size of a mail queue. The queue goes to warning 
when there are say 350 messages in the queue.
Because of the nature of a mail queue it might float around this threshold for 
some time. It might even end up in a flapping state.

What if it were to not go back to an ok state unless the size of the queue 
were to go below 300. 

Plugins could have hysteresis values optionally specified on their command 
lines. If it was specified then the previous state would also need to be 
provided so the plugin could determine if the hysteresis value should be 
considered. 

ie: previous state is ok, then hysteresis value is irrelevant.
if the previous state is warning then the hysteresis value should be 
considered if the new state is to be ok.

It's possible this behaviour could be implemented as utility functions dealing 
with absolute values. These functions would determine the returned state 
based on the value, previous state and new state.

-- 
-- Sam


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