Github user bowenli86 commented on the issue:
https://github.com/apache/flink/pull/5500
@tillrohrmann @kl0u Thanks for reviewing, guys
As @pnowojski mentioned, we three decided to expose timer keys in
`ProcessFunction` in [FLINK-8560](https://github.com/apache/flink/pull/5481).
Exposing timer keys in `KeyedBroadcastProcessFunction` extends that design. I
think we should get this PR into 1.5.0 so we don't need to do the [complicated
refactoring for FLINK-8560](https://github.com/apache/flink/pull/5481) to
support backward compatibility
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