Github user fhueske commented on the issue:
https://github.com/apache/flink/pull/3783
Thanks for this PR @huawei-flink!
I think I made a mistake when I suggested to use the code-gen'd functions
with registered `MapState` to compute distinct window aggregations. Originally,
I thought it would be possible to register state (i.e., the `MapState` for the
distinct values) in an `AggregateFunction` (which is used for the grouped
window aggregates). However, that's unfortunately not possible as I learned
today. All state of an `AggregateFunction` must be contained in the accumulator.
What does this mean? We cannot use the current approach of registering
`MapState` in the code-gen'd function for group windowed aggregates. So we
would need another approach for that.
However, we can still use your code for distinct over windows
(`ProcessFunction` can obviously register state) once the API supports to
define DISTINCT aggregates.
I'll try to have a closer look at this PR soon.
Best, Fabian
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