Hi Mans, For understanding the difference between FIRE and FIRE_AND_PURGE it's helpful to look at the cases where it really makes a difference. In my opinion this only makes a difference when you have event-time windowing and when you have multiple firing for the same window (i.e. multiple firings for the window [12:00,13:00) for a key x). You have this either when you have late data or when you have a custom trigger that can fire speculatively. Let's look at the first case and see where FIRE/FIRE_AND_PURGE act differently.
Assume we have window assigner = "tumbling windows of 10 ms" and allowed lateness 5 ms. We get this data: event1, ts = 1 watermark, ts = 11 event2, ts = 2 What we get from this is a firing when the watermark arrives with the window contents (event1) for window [0, 9). Then, when event2 arrives we get a second firing (because the default event-time trigger will FIRE when late data arrives for a window) for window [0, 9) with contents (event1, event2) if our trigger returns FIRE or with contents (event2) if our trigger returns FIRE_AND_PURGE. If we had allowed lateness 0 ms we wouldn't have the second firing for the late event and we wouldn't see a difference between FIRE and FIRE_AND_PURGE. This can be extended to the second case of a custom trigger that might fire early (based on the count of events in the window or processing time). I hope this helps. Aljoscha > On 20. Nov 2017, at 11:18, Stefan Richter <s.rich...@data-artisans.com> wrote: > > Hi, > >> >> "In the first case, it is a new window without the previous elements, in the >> second case the window reflects the old contents plus all changes since the >> last trigger." >> >> I am assuming the first case is FIRE and second case is FIRE_AND_PURGE - I >> was thinking that in the first case (FIRE), there would be elements from >> previous window since we did not purge and the second case it would have >> only new elements since it was purged. Am I missing something ? >>> > > No, with first case, I meant the „truly new window case“ and the second case > is „another triggering of the previous (non-purged) window“. So the second > case is a simple FIRE without PURGE. > > Best, > Stefan
