I would use Reshuffle()[1] with entity id as the key. It internally does a GroupByKey and sets up windowing such that it does not buffer anything.
[1] : https://github.com/apache/beam/blob/master/sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Reshuffle.java#L51 On Fri, Jul 6, 2018 at 8:01 AM Niels Basjes <ni...@basjes.nl> wrote: > Hi, > > I have an unbounded stream of change events each of which has the id of > the entity that is changed. > To avoid the need for locking in the persistence layer that is needed in > part of my processing I want to route all events based on this entity id. > That way I know for sure that all events around a single entity go through > the same instance of my processing sequentially, hence no need for locking > or other synchronization regarding this persistence. > > At this point my best guess is that I need to use the GroupByKey but that > seems to need a Window. > I think I don't want a window because the stream is unbounded and I want > the lowest possible latency (i.e. a Window of 1 second would be ok for this > usecase). > Also I want to be 100% sure that all events for a specific id go to only a > single instance because I do not want any race conditions. > > My simple question is: What does that look like in the Beam Java API? > > -- > Best regards / Met vriendelijke groeten, > > Niels Basjes >
