Hi Dongwon Kim, That's an interesting question.
I don't have a solution blueprint for you, but a few ideas that should help to solve the problem. I would start with a separate job first and later try to integrate it with the other job. You could implement a Trigger that fires when a new window is created and when the window is closed. A ProcessWindowFunction would emit a +1 if the window was created and a -1 when the window is closes. Session windows are a bit special, because you also need to handle the case of merging windows, i.e., two opened windows can be merged and only one (the merged) window is closed. So would need to emit a -2 if a merged window was closes (assuming only two windows were merged). In order to do that, you'd need to carry the merging information forward. The Trigger.onMerge method cannot trigger the window function, but it could store the merging information in state that is later accessed. Hope this helps, Fabian 2018-02-20 9:54 GMT+01:00 Dongwon Kim <eastcirc...@gmail.com>: > Hi, > > It could be a totally stupid question but I currently have no idea how to > get the number of active session windows from a running job. > > Our traffic trajectory application (which handles up to 10,000 tps) uses > event-time session window on KeyedStream (keyed by userID). > > Should I write another Flink job for the purpose? > > Cheers, > > Dongwon Kim
