Hi Dongwon, On Sat, Aug 22, 2020 at 2:46 PM Dongwon Kim <eastcirc...@gmail.com> wrote:
> Hi all, > > I'm using Beam 2.23.0 with FlinkRunner and a part of my unbounded pipeline > looks like below: > >> p.apply(WithKeys.of(...).withKeyType(...)) // (A) >> .apply(Window.into(FixedWindows.of(...))) // (B) > > .apply(Combine.perKey(new MyCombinFn())) // (C) > > .apply(ParDo.of(new MyDoFn())) // (D) > > > What I want to do is > (1) to group data by key (A) and window (B), > (2) to do some aggregation (C) > (3) to perform the final computation on each group (D) > > I've noticed that a ValueState for a particular key is NULL whenever a new > window for the key is arriving, which gives me a feeling that Beam seems to > support only per-key+window state, not per-key state, after windowing. > > I usually work with Flink DataStream API and Flink supports both per-key > state and per-key+window state [1]. > > Does Beam support per-key states, not per-key+window states, after > windowing (D)? If I miss something, please correct me. > You understand correctly - Beam does not include per-key state that crosses window boundaries. If I understand your goal correctly, you can achieve the same effect by copying the window metadata into the element and then re-windowing into the global window before (D). Kenn > > [1] > https://ci.apache.org/projects/flink/flink-docs-stable/dev/stream/operators/windows.html#using-per-window-state-in-processwindowfunction > > Best, > > Dongwon > >
