[jira] [Commented] (FLINK-16193) Improve error messaging when a key is assigned to the wrong key group range

["Seth Wiesman (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-16193?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17041272#comment-17041272 ] 

Seth Wiesman commented on FLINK-16193:
--------------------------------------

[~aljoscha]

This is tricky because key group ranges are not validated in one place but all over the codebase, at low-level places around the state backends. I _think_ we could simply include a check at AbstractStreamOperator#setKeyContextElement and throw an exception there. This seems safe to me but I want to double check.

> Improve error messaging when a key is assigned to the wrong key group range
> ---------------------------------------------------------------------------
>
>                 Key: FLINK-16193
>                 URL: https://issues.apache.org/jira/browse/FLINK-16193
>             Project: Flink
>          Issue Type: Improvement
>          Components: API / DataStream
>    Affects Versions: 1.11.0
>            Reporter: Seth Wiesman
>            Priority: Major
>
> Occasionally, users may run into an exception that reads something like:
>  
> java.lang.IllegalArgumentException: Key group 45 is not in KeyGroupRange{startKeyGroup=0, endKeyGroup=42}
>  
> This may be caused by a number of issues including:
> 1) Unstable hash and equals methods on their key objects
> 2) Improper use of DataStreamUtils#reinterpretAsKeyedStream
>  
> Key group ranges are a fairly low level detail that most users will be unfamiliar with when working with Flink. We should offer more comprehensive error messaging that outlines likely causes and solutions.
>  



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