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From Will Benton <wi...@redhat.com>
Subject Re: Kryo serialization for closures: a workaround
Date Wed, 28 May 2014 20:13:06 GMT
This is an interesting approach, Nilesh!

Someone will correct me if I'm wrong, but I don't think this could go into ClosureCleaner
as a default behavior (since Kryo apparently breaks on some classes that depend on custom
Java serializers, as has come up on the list recently).  But it does seem like having a function
in Spark that did this for closures more transparently (to be called explicitly by clients
in problem cases) could be pretty useful.


best,
wb


----- Original Message -----
> From: "Nilesh" <nilesh@nileshc.com>
> To: dev@spark.incubator.apache.org
> Sent: Saturday, May 24, 2014 10:32:57 AM
> Subject: Kryo serialization for closures: a workaround
> 
> Suppose my mappers can be functions (def) that internally call other classes
> and create objects and do different things inside. (Or they can even be
> classes that extend (Foo) => Bar and do the processing in their apply method
> - but let's ignore this case for now)
> 
> Spark supports only Java Serialization for closures and forces all the
> classes inside to implement Serializable and coughs up errors when forced to
> use Kryo for closures. But one cannot expect all 3rd party libraries to have
> all classes extend Serializable!
> 
> Here's a workaround that I thought I'd share in case anyone comes across
> this problem:
> 
> You simply need to serialize the objects before passing through the closure,
> and de-serialize afterwards. This approach just works, even if your classes
> aren't Serializable, because it uses Kryo behind the scenes. All you need is
> some curry. ;) Here's an example of how I did it:
> 
> def genMapper(kryoWrapper: KryoSerializationWrapper[(Foo => Bar)])
> (foo: Foo) : Bar = {    kryoWrapper.value.apply(foo)}val mapper =
> genMapper(KryoSerializationWrapper(new Blah(abc)))
> _rdd.flatMap(mapper).collectAsMap()object Blah(abc: ABC) extends (Foo =>
> Bar) {    def apply(foo: Foo) : Bar = { //This is the real function }}
> Feel free to make Blah as complicated as you want, class, companion object,
> nested classes, references to multiple 3rd party libs.
> 
> KryoSerializationWrapper refers to  this wrapper from amplab/shark
> <https://github.com/amplab/shark/blob/master/src/main/scala/shark/execution/serialization/KryoSerializationWrapper.scala>
> 
> Don't you think it's a good idea to have something like this inside the
> framework itself? :)
> 
> 
> 
> --
> View this message in context:
> http://apache-spark-developers-list.1001551.n3.nabble.com/Kryo-serialization-for-closures-a-workaround-tp6787.html
> Sent from the Apache Spark Developers List mailing list archive at
> Nabble.com.

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