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https://issues.apache.org/jira/browse/FLINK-16555?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17061342#comment-17061342
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Lu Niu commented on FLINK-16555:
--------------------------------

Is someone working on this? If not, could you assign it to me? I used to work 
on presto and now move to flink. I think this task would be great to help me 
understand flink type system. 

> Preflight check for known unstable hashCodes.
> ---------------------------------------------
>
>                 Key: FLINK-16555
>                 URL: https://issues.apache.org/jira/browse/FLINK-16555
>             Project: Flink
>          Issue Type: Improvement
>          Components: API / DataStream, API / Type Serialization System
>            Reporter: Stephan Ewen
>            Priority: Critical
>              Labels: usability
>             Fix For: 1.11.0
>
>
> Data types can only be used as keys, if they have a stable hash code 
> implementation that is deterministic across JVMs. Otherwise, the keyBy() 
> operations will result in incorrect data routing.
> We should eagerly check the key type information for known cases types with 
> unstable hash code, such as
> * arrays
> * enums
> * anything that does not override Object.hashCode



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