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https://issues.apache.org/jira/browse/FLINK-11947?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16850497#comment-16850497
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Congxian Qiu(klion26) commented on FLINK-11947:
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[~cresny] I'm interested in this issue, and wanna give a fix for this. I'm
happy [~tzulitai] will shepherd the effort.
> Support MapState key / value schema evolution for RocksDB
> ---------------------------------------------------------
>
> Key: FLINK-11947
> URL: https://issues.apache.org/jira/browse/FLINK-11947
> Project: Flink
> Issue Type: Improvement
> Components: API / Type Serialization System, Runtime / State Backends
> Reporter: Tzu-Li (Gordon) Tai
> Priority: Critical
>
> Currently, we do not attempt to perform state schema evolution if the key or
> value's schema of a user {{MapState}} has changed when using {{RocksDB}}:
> https://github.com/apache/flink/blob/953a5ffcbdae4115f7d525f310723cf8770779df/flink-state-backends/flink-statebackend-rocksdb/src/main/java/org/apache/flink/contrib/streaming/state/RocksDBKeyedStateBackend.java#L542
> This was disallowed in the initial support for state schema evolution because
> the way we did state evolution in the RocksDB state backend was simply
> overwriting values.
> For {{MapState}} key evolution, only overwriting RocksDB values does not
> work, since RocksDB entries for {{MapState}} uses a composite key containing
> the map state key. This means that when evolving {{MapState}} in this case
> with an evolved key schema, we will have new entries.
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