damccorm opened a new issue, #20436:
URL: https://github.com/apache/beam/issues/20436

   The Go SDK currently retains an arbitrary timestamp per key per bundle when 
performing a lifted combine. 
   However, depending on the windowing strategy, a prefered time could be 
specified.
   
https://github.com/apache/beam/blob/a5b2046b10bebc59c5bde41d4cb6498058fdada2/model/pipeline/src/main/proto/beam_runner_api.proto#L901
   
   The code in question for the Go SDK:
   
https://github.com/apache/beam/blob/master/sdks/go/pkg/beam/core/runtime/exec/combine.go#L395
   
   At present this implementation is "correct", as the default output time is 
Unspecified, and there's no user mechanism to configure a windowing strategy to 
this granularity.
   
   So there are a few parts to this.
   1. Propagate the windowing strategy information to exec.LiftedCombine 
somehow and implement the correct output. This can be done whether or not 2 is 
implemented.
   2. Provide a trigger configuration for beam.WindowInto, so this can be 
configured on the user side. This is significantly more work.
   
   This matters only when using windows that are not the Global Window, and 
when using a Lifted Combine, which commonly only happens in batch contexts. 
However, since Beam is a unified model, the windowing features should work 
correctly in both execution modes of a Go SDK pipeline.
   
   
   
   
   
   Imported from Jira 
[BEAM-10302](https://issues.apache.org/jira/browse/BEAM-10302). Original Jira 
may contain additional context.
   Reported by: lostluck.


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