[jira] [Commented] (SPARK-19938) java.lang.ClassCastException: cannot assign instance of scala.collection.immutable.List$SerializationProxy to field

["Igor Kamyshnikov (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-19938?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17200272#comment-17200272 ] 

Igor Kamyshnikov commented on SPARK-19938:
------------------------------------------

[~rdblue], my analysis shows the different root cause of the problem:
https://bugs.openjdk.java.net/browse/JDK-8024931
https://github.com/scala/bug/issues/9777

It's about circular references among the objects being serialized:

RDD1.dependencies_ = Seq1[RDD2]
RDD2.dependences_ = Seq2[RDD3]
RDD3 with some Dataset/catalyst magic can refer back to the Seq1[RDD2]

Seq are instances of scala.collection.immutable.List which uses writeReplace, giving an instance of 'SerializationProxy'. The serialization of RDD3 puts a reference to the Seq1's SerializationProxy. When the deserialization works, it reads that reference to SerializationProxy earlier than the 'readResolve' method is called (see the JDK bug reported).

> java.lang.ClassCastException: cannot assign instance of scala.collection.immutable.List$SerializationProxy to field
> -------------------------------------------------------------------------------------------------------------------
>
>                 Key: SPARK-19938
>                 URL: https://issues.apache.org/jira/browse/SPARK-19938
>             Project: Spark
>          Issue Type: Bug
>          Components: Tests
>    Affects Versions: 2.0.2
>            Reporter: srinivas thallam
>            Priority: Major
>




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