Tzu-Li (Gordon) Tai created FLINK-6025:
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Summary: User code ClassLoader not used when KryoSerializer
fallbacks to serialization for copying
Key: FLINK-6025
URL: https://issues.apache.org/jira/browse/FLINK-6025
Project: Flink
Issue Type: Bug
Components: Type Serialization System
Reporter: Tzu-Li (Gordon) Tai
Reported in ML:
http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/AWS-exception-serialization-problem-td12063.html
This is a known Kryo issue with its {{JavaSerializer}}:
https://github.com/EsotericSoftware/kryo/pull/483.
It happens when a {{Throwable}} is to be copied by the {{KryoSerialzer}}. Since
we use the {{JavaSerializer}} for throwables, and {{JavaSerializer}} doesn't
support copying, the {{KryoSerializer}} fallbacks to use de-/serialization for
the throwable. The problem is that on deserialization, the classloader that the
{{ObjectInputStream}} uses may be overriden, and doesn't specifically uses
Kryo's configured classloader (i.e., the user code class loader), and results
in {{ClassNotFoundException}}.
Generally, this may happen if the user also registers to use the
{{JavaSerializer}} for their types.
To fix the problem for {{Throwable}} serializing in the {{KryoSerializer}}, we
could either consider registering our own {{JavaSerializer}} that fixes this
problem, or wait for the Kryo fix to be released (to be fixed in Kryo 4.0.1
release).
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