问题
is it possible to detect the absence of a certain event type within a given time window without using any other event types in Esper?
Thanx ;)
回答1:
You can take a look at the solution patterns here for some ideas: http://www.espertech.com/esper/solution-patterns#absence-1
Here is an adapted example of detecting an absence of an event, after it has been fired once:
select * from pattern [every EventX -> (timer:interval(10 sec) and not EventX)];
This will fire only once, if after an EventX is received, no other EventX arrives within 10 seconds...
This example:
select * from pattern [every (timer:interval(10 sec) and not EventX)];
Will fire every 10 seconds if no EventX has been receive during that time (and keep firing like this forever).
回答2:
Outer joins are also a good way to detect the absence of an event.
来源：https://stackoverflow.com/questions/31796373/esper-detect-absence-of-a-certain-event