[jira] [Commented] (FLINK-6388) Add support for DISTINCT into Code Generated Aggregations

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-6388?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15986851#comment-15986851 ] 

ASF GitHub Bot commented on FLINK-6388:
---------------------------------------

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


> Add support for DISTINCT into Code Generated Aggregations
> ---------------------------------------------------------
>
>                 Key: FLINK-6388
>                 URL: https://issues.apache.org/jira/browse/FLINK-6388
>             Project: Flink
>          Issue Type: Sub-task
>          Components: DataStream API
>    Affects Versions: 1.3.0
>            Reporter: Stefano Bortoli
>            Assignee: Stefano Bortoli
>             Fix For: 1.3.0
>
>
> We should support DISTINCT in Code Generated aggrgation functions.



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