tzulitai opened a new pull request #6931: [FLINK-9808] [state-backends] Migrate state when necessary URL: https://github.com/apache/flink/pull/6931 ## What is the purpose of the change This PR is based on #6930. Only the last commit is relevant. This PR adds the procedure of migrating state (i.e., reading state bytes with the restored prior serializer, and then re-writing the deserialized object with the new serializer). - This should only ever occur in the RocksDB state backend, since the restore / snapshotting of heap-based backends are already a migration process by nature. This is identified by a result of `TypeSerializerSchemaCompatibility.compatibleAfterMigration()` on the state serializer's compatibility check. - For heap-based backends, we only need to check that the new state serializer isn't incompatible. This is identified by a result of `TypeSerializerSchemaCompatibility.incompatible()` on the state serializer's compatibility check. ## Brief change log - Add `migrateSerializedValue` to `AbstractRocksDBStateValue` - Use the new method to iterate through RocksDB bytes when state migration is necessary - Adapt heap-based backends to check fail when new serializers are incompatible. - Add a `StateMigrationTestBase` that verifies serializers are being used as expected for a restore procedure ## Verifying this change The main new test coverage that covers this is in the `StateMigrationTestBase` class. ## Does this pull request potentially affect one of the following parts: - Dependencies (does it add or upgrade a dependency): (yes / **no**) - The public API, i.e., is any changed class annotated with `@Public(Evolving)`: (yes / **no**) - The serializers: (**yes** / no / don't know) - The runtime per-record code paths (performance sensitive): (**yes** / no / don't know) - Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (**yes** / no / don't know) - The S3 file system connector: (yes / **no** / don't know) ## Documentation - Does this pull request introduce a new feature? (**yes** / no) - If yes, how is the feature documented? (not applicable / docs / **JavaDocs** / not documented)
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