Tzu-Li (Gordon) Tai created FLINK-6363:
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Summary: Document precedence rules of Kryo serializer registrations
Key: FLINK-6363
URL: https://issues.apache.org/jira/browse/FLINK-6363
Project: Flink
Issue Type: Improvement
Components: Documentation, Type Serialization System
Reporter: Tzu-Li (Gordon) Tai
Assignee: Tzu-Li (Gordon) Tai
Currently, there is no documentation / Javadoc mentioning the precedence rules
of Kryo registrations via the register methods in
{{StreamExecutionEnvironment}} / {{ExecutionEnvironment}}.
It is important for the user to be notified of the precedence because the
{{KryoSerializer}} applies the configurations in a specific order that is not
visible from the public API.
For example:
{code}
env.addDefaultKryoSerializer(SomeClass.class, SerializerA.class);
env.addDefaultKryoSerializer(SomeClass.class, new SerializerB());
{code}
from this API usage, it may seem as if {{SerializerA}} will be used as the
default serializer for {{SomeClass}} (or the other way around, depends really
on how the user perceives this).
However, whatever the called order in this example, {{SerializerB}} will always
be used because in the case of defining default serializers, due to the
ordering that the internal {{KryoSerializer}} applies these configurations,
defining serializer instance has a higher precedence than defining with
serializer class.
These methods are also subject to the same issue:
{code}
env.registerType(SomeClass.class, SerializerA.class);
env.registerTypeWithKryoSerializer(SomeClass.class, SerializerA.class);
env.registerTypeWithKryoSerializer(SomeClass.class, new SerializerB());
{code}
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