JingsongLi commented on issue #1438:
URL: https://github.com/apache/iceberg/issues/1438#issuecomment-692425245


   Hi, I think there are two cases:
   1. Restoring Flink job from checkpoint/savepoint state.
   2. Flink cluster upgraded with existing user applications.
   
   In Flink, for serializing checkpoint state:
   - For known objects, such as POJO, List, etc., Flink uses handwritten 
serializers.
   - For unknown objects, Flink uses Kryo serializer. [1]
   
   So actually, Flink not use Java serialization to serialize checkpoint state. 
So I think case 1 may not be a valid problem. (If Iceberg objects are good to 
upgrade using Kryo)
   
   Case 2 is indeed a problem, From another perspective, can we consider 
customizing the Java serializer of `RowDataTaskWriterFactory`?
   
   
[1]https://ci.apache.org/projects/flink/flink-docs-master/dev/types_serialization.html#general-class-types


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