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  1. Flink
  2. FLINK-9376 Allow upgrading to incompatible state serializers (state schema evolution)
  3. FLINK-9377

Remove writing serializers as part of the checkpoint meta information

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      When writing meta information of a state in savepoints, we currently write both the state serializer as well as the state serializer's configuration snapshot.

      Writing both is actually redundant, as most of the time they have identical information.
      Moreover, the fact that we use Java serialization to write the serializer and rely on it to be re-readable on the restore run, already poses problems for serializers such as the AvroSerializer (see discussion in FLINK-9202) to perform even a compatible upgrade.

      The proposal here is to leave only the config snapshot as meta information, and use that as the single source of truth of information about the schema of serialized state.
      The config snapshot should be treated as a factory (or provided to a factory) to re-create serializers capable of reading old, serialized state.

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              tzulitai Tzu-Li (Gordon) Tai
              tzulitai Tzu-Li (Gordon) Tai
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