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https://issues.apache.org/jira/browse/FLINK-37524?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17937852#comment-17937852
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Yue Ma commented on FLINK-37524:
--------------------------------

[~Yanfei Lei] Thanks very much for your reply.

Yes, as you mentioned , ForStKeyedStateBackend implement 
`tryRegisterKvStateInformation` and will updateRestoredStateMetaInfo if 
restored from checkpoint.

But the main problem is that the `StateSerializer` information in `newMetaInfo` 
is not used in the constructor of `AbstractKeyedState`. Instead, it directly 
used the information in StateDescriptor as the `StateSerializer`. 
[https://github.com/apache/flink/blob/c151909d5a0d3568178c1a984da76b39d7e94dee/flink-runtime/src/main/java/org/apache/flink/runtime/state/v2/AbstractKeyedState.java#L57
 . 
|https://github.com/apache/flink/blob/c151909d5a0d3568178c1a984da76b39d7e94dee/flink-runtime/src/main/java/org/apache/flink/runtime/state/v2/AbstractKeyedState.java#L57]Therefore,
 the old State Serializer in Checkpoint is not actually used. 
I'm not sure if I expressed myself clearly.

> State Serializer in ForState should restore from oldStateInfo in Checkpoint
> ---------------------------------------------------------------------------
>
>                 Key: FLINK-37524
>                 URL: https://issues.apache.org/jira/browse/FLINK-37524
>             Project: Flink
>          Issue Type: Bug
>          Components: Runtime / State Backends
>    Affects Versions: 2.0.0
>            Reporter: Yue Ma
>            Priority: Major
>             Fix For: 2.1.0
>
>
> Currently, when creating using ForStKeyedStateBackend create a new State , 
> *_AbstractKeyedState_* will directly use the serializer in 
> _*StateDescriptor*_ regardless of whether it is restored from a Checkpoint.
> However, this may cause data to be unable to be restored when the last 
> serializer changes (for example, the class registration order in 
> *_KryoSerializer_* has changed, for specific cases, please refer to 
> {*}_StateBackendTestBase#testKryoRestoreResilienceWithDifferentRegistrationOrder_{*}).
>  Therefore, when creating a State from a Checkpoint, oldStateInfo should be 
> used as the new State's Serializer.



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