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 >>> >>> >>> >>>
