I think one "edge" case which is not handled would be that the first event (by event-time) arrives late, then a wrong "started-window" would be reported.
Rafi On Thu, Feb 20, 2020 at 12:36 PM Manas Kale <manaskal...@gmail.com> wrote: > Is the reason ValueState cannot be use because session windows are always > formed by merging proto-windows of single elements, therefore a state store > is needed that can handle merging. ValueState does not provide this > functionality, but a ReducingState does? > > On Thu, Feb 20, 2020 at 4:01 PM Manas Kale <manaskal...@gmail.com> wrote: > >> Hi Till, >> Thanks for your answer! You also answered the next question that I was >> about to ask "Can we share state between a Trigger and a Window?" Currently >> the only (convoluted) way to share state between two operators is through >> the broadcast state pattern, right? >> Also, in your example, why can't we use a ValueStateDescriptor<Boolean> >> in the Trigger? I tried using it in my own example but it I am not able >> to call the mergePartitionedState() method on a ValueStateDescriptor. >> >> Regards, >> Manas >> >> >> >> On Tue, Feb 18, 2020 at 7:20 PM Till Rohrmann <trohrm...@apache.org> >> wrote: >> >>> Hi Manas, >>> >>> you can implement something like this with a bit of trigger magic. What >>> you need to do is to define your own trigger implementation which keeps >>> state to remember whether it has triggered the "started window" message or >>> not. In the stateful window function you would need to do something >>> similar. The first call could trigger the output of "window started" and >>> any subsequent call will trigger the evaluation of the window. It would >>> have been a bit easier if the trigger and the window process function could >>> share its internal state. Unfortunately, this is not possible at the moment. >>> >>> I've drafted a potential solution which you can find here [1]. >>> >>> [1] >>> https://gist.github.com/tillrohrmann/5251f6d62e256b60947eea7b553519ef >>> >>> Cheers, >>> Till >>> >>> On Mon, Feb 17, 2020 at 8:09 AM Manas Kale <manaskal...@gmail.com> >>> wrote: >>> >>>> Hi, >>>> I want to achieve the following using event time session windows: >>>> >>>> 1. When the window.getStart() and last event timestamp in the >>>> window is greater than MIN_WINDOW_SIZE milliseconds, I want to emit a >>>> message "Window started @ timestamp". >>>> 2. When the session window ends, i.e. the watermark passes >>>> lasteventTimestamp + inactivityPeriod, I want to emit a message "Window >>>> ended @ timestamp". >>>> >>>> It is guaranteed that all events are on time and no lateness is >>>> allowed. I am having difficulty implementing both 1 and 2 simultaneously. >>>> I am able to implement point 1 using a custom trigger, which checks if >>>> (lastEventTimestamp - window.getStart()) > MIN_WINDOW_SIZE and triggers a >>>> customProcessWindowFunction(). >>>> However, with this architecture I can't detect the end of the window. >>>> >>>> Is my approach correct or is there a completely different method to >>>> achieve this? >>>> >>>> Thanks, >>>> Manas Kale >>>> >>>> >>>> >>>>
