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Re: Identifying missing events in keyed streams


Hi Averell,

I'd go with approach 2). As of Flink 1.6.0 you can delete timers. 

But even if you are on a pre-1.6 version, a ProcessFunction would be the way to go, IMO.
You don't need to register a timer for each event.
Instead, you can register the first timer with the first event and have a state that is updated with the timestamp of the last seen event.
When the timer fires, you check the if you need to raise an alert and register a new timer such that it fires 1 minute after the last seen event (last-seen + 1 minute - (now - last-seen)).

Best, Fabian

Am Do., 4. Okt. 2018 um 16:15 Uhr schrieb Averell <lvhuyen@xxxxxxxxx>:
Hi everyone,

I have a keyed stream which is expecting events every fixed interval (let's
say 1 minute). I want to raise alarms for any key which has received no
events in n-periods. What should be the cheapest way (in term of performance
) to do this?
I thought of some solutions, but don't know which one is the best:
1. Sliding window then count the number of events in each window <<< this
seems quite expensive when n is big.
2. Register a timer for every single event, record the last event timestamp
and check that timestamp when the timer expires. (This would be the best if
there's an option to cancel/modify a timer, but it seems that feature is not
available yet)
3. Session window: i haven't implemented this to verify its feasibility.
Thinking of firing the alarm on every window clear event.
4. CEP. I don't know whether it's possible or not. Haven't found a guide for
defining patterns of missing events.

Could you please give some advices?

Thanks and best regards,
Averell



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