A bit more information: graphx/translate.go has the handling of WindowingStrategy at pipeline encoding and we only use Non Merging.
Presumably this is something that would need to be fixed when supporting Session windows in BEAM-4152 On Thu, Feb 18, 2021, 10:02 AM Robert Burke <rob...@frantil.com> wrote: > Go has very basic windowing support that is managed entirely by the > runner. Session windowing isn't implemented yet, let alone custom windowfns > which i asume is what would need to specify these things. > > Session windowing is tracked in BEAM-4152 > and Custome windowFns are tracked in BEAM-11100. > > On Wed, Feb 17, 2021, 12:06 PM Kenneth Knowles <k...@apache.org> wrote: > >> Hi all, >> >> Yet another exciting corner of portability, discovered during debugging. >> Some discussion at https://github.com/apache/beam/pull/14001 and >> https://github.com/apache/beam/pull/13998 >> >> **In Java since around the beginning of Beam** >> When a merging WindowFn goes through a GBK/Combine and windows are >> merged, the downstream windowing is changed to "InvalidWindows" which will >> fail any downstream GBK. The user is required to re-window before another >> GBK. >> >> It was to protect a user from this: >> >> 1. User sets keys and chooses session windowing >> 2. User groups/combines by session >> 3. User computes the outputs to produce some new keys >> 4. User groups again >> >> The result usually does not make sense. Because it was forbidden we never >> decided whether things should merge again or not. >> >> **In protos** >> The MergeStatus enum has NON_MERGING, NEEDS_MERGE, and ALREADY_MERGED. It >> is documented that ALREADY_MERGED is for sessions/merging windows after a >> GBK. >> >> This is _maybe_ better. It allows the windows to just be carried along. >> It is a major model change and would require SDK support. But it might >> still not make sense because the chances that two elements have exactly the >> same merging window are very low for something like sessions. It may be >> useful for advanced tricks with merging windows, but noone is doing that >> because no SDK supports it. >> >> **In Python** >> I think nothing is done. The next GBK will merge again. I could be wrong >> - I just read the code very quickly and don't know it that well. >> >> **In Go** >> I didn't even check. Maybe someone can add the status to the thread. >> >> Kenn >> >
