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https://issues.apache.org/jira/browse/SPARK-7708?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14548282#comment-14548282
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Akshat Aranya commented on SPARK-7708:
--------------------------------------
This happens because the TaskDescription contains a SerializableBuffer, which
has no fields from the point of view of Kryo. It only has a transient var and
a def. When this is serialized by Kryo, it finds no member fields to
serialize, so it doesn't write out the underlying buffer.
> Incorrect task serialization with Kryo closure serializer
> ---------------------------------------------------------
>
> Key: SPARK-7708
> URL: https://issues.apache.org/jira/browse/SPARK-7708
> Project: Spark
> Issue Type: Bug
> Components: Spark Core
> Affects Versions: 1.2.2
> Reporter: Akshat Aranya
>
> I've been investigating the use of Kryo for closure serialization with Spark
> 1.2, and it seems like I've hit upon a bug:
> When a task is serialized before scheduling, the following log message is
> generated:
> [info] o.a.s.s.TaskSetManager - Starting task 124.1 in stage 0.0 (TID 342,
> <host>, PROCESS_LOCAL, 302 bytes)
> This message comes from TaskSetManager which serializes the task using the
> closure serializer. Before the message is sent out, the TaskDescription
> (which included the original task as a byte array), is serialized again into
> a byte array with the closure serializer. I added a log message for this in
> CoarseGrainedSchedulerBackend, which produces the following output:
> [info] o.a.s.s.c.CoarseGrainedSchedulerBackend - 124.1 size=132
> The serialized size of TaskDescription (132 bytes) turns out to be _smaller_
> than serialized task that it contains (302 bytes). This implies that
> TaskDescription.buffer is not getting serialized correctly.
> On the executor side, the deserialization produces a null value for
> TaskDescription.buffer.
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