Github user liancheng commented on the pull request:
https://github.com/apache/spark/pull/3640#issuecomment-66319557
The current design of this PR is derived from some background knowledges.
I'd like to provide a brief summary here for future reference.
As mentioned in the PR description, different from Hive 0.12.0, in Hive
0.13.1 UDF/UDAF/UDTF (aka Hive function) objects should only be initialized
once on the driver side and then serialized to executors. However, not all
function objects are serializable (e.g. `GenericUDF` doesn't implement
`Serializable`). Hive 0.13.1 solves this issue with Kryo or XML serializer.
Several utility ser/de methods are provided in class `o.a.h.h.q.e.Utilities`
for this purpose. In this PR we chose Kryo for efficiency. The Kryo serializer
used here is created in Hive. Spark Kryo serializer wasn't used because there's
no available `SparkConf` instance.
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