Tzu-Li (Gordon) Tai created FLINK-11917:
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Summary: Allow state schema migration from Kryo to POJO / Avro
Key: FLINK-11917
URL: https://issues.apache.org/jira/browse/FLINK-11917
Project: Flink
Issue Type: Improvement
Components: API / Type Serialization System
Reporter: Tzu-Li (Gordon) Tai
In Flink, it has been commonly advertised that users should try to avoid Kryo
for state serialization since it doesn't work out-of-the-box well for schema
evolution stories. Kryo, in the first place, wasn't designed with that in mind.
In light of this, Flink should provide a migration path for state that were
default to be serialized by the {{KryoSerializer}} to other serializers that
now support better schema evolution capabilities, such as {{PojoSerializer}}
and {{AvroSerializer}}.
Essentially, what this means is that in the {{KryoSerializerSnapshot}} class's
{{resolveSchemaCompatibility}} method, we identify if the new serializer is
either {{PojoSerializer}} or {{AvroSerializer}}; if so, we return
{{TypeSerializerSchemaCompatibility.compatibleAfterMigration()}} as the result.
For the user, this would allow them to simply upgrade their state types to be
Avro-generated {{SpecificRecord}} or a qualified POJO.
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