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https://issues.apache.org/jira/browse/SPARK-27237?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16798465#comment-16798465
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Jungtaek Lim commented on SPARK-27237:
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Working on this.
> Introduce State schema validation among query restart
> -----------------------------------------------------
>
> Key: SPARK-27237
> URL: https://issues.apache.org/jira/browse/SPARK-27237
> Project: Spark
> Issue Type: Improvement
> Components: Structured Streaming
> Affects Versions: 3.0.0
> Reporter: Jungtaek Lim
> Priority: Major
>
> Even though Spark structured streaming guide page clearly documents that "Any
> change in number or type of grouping keys or aggregates is not allowed.",
> Spark doesn't do anything when end users try to do it, which would end up
> with indeterministic outputs or unexpected exceptions.
> Even worse, if the query doesn't crash by chance it could write the new
> messed values to state which completely breaks state unless end users roll
> back to specific batch via manually editing checkpoint.
> The restriction is clear, the number of columns, and data type for each must
> not be modified among query runs. We can store schema of state along with
> state, and verify whether the (maybe) new schema is compatible if state
> schema is modified.
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