Relative alerts in chronograf

chronograf
kapacitor
time-series
#1

I have the following Question concerning relative alerts.

Assume I have a “descending” time sequence with one data element per 0.5 seconds. Every 8 seconds I want to check if the data elements received in the last 10 seconds have descreased more than a value x, e.g. something like:

20 20 21 19 19 19 20 19 17 20 19 19 19 8 8 8 7 7 7 8 8 9 7 8 8 8 8
Should I define the following values in the generated TICKscript:
period=10s
every=8s
shift=10s
crit=-x
If I do so - how often will this rule be executed? Every 10 s?

Thanks

#2

I @kpeckert,

Great question! The difference between period and every can be a bit confusing (it’s bitten me several times as well!). In general, the idea is that period is the span of time over which you want to evaluate data while every is how often you want to do this. So in your example above, the script would evaluate 10 seconds worth of data every 8 seconds, so the rule would be executed every 8 seconds.

If this wasn’t clear enough, feel free to ask follow-up questions!

Best Regards,
dg

#3

Ok - thanks.

Thus “every” defines how often the script will run and “period” defines the length of the evaluation interval. “Shifts” defines the delay I want to use to compare data.
Is it true that in case shift>period I will never get an alert?