apache/spark — pull request #499 by jegonzal (2014-04-23 06:02:12+00:00)
Title: SPARK-1577: Enabling reference tracking by default in GraphX KryoRegistrator.

We had originally disabled reference tracking by default however this now seems to create serious issues in the spark-shell where even the following benign block of code will fail:

```scala
class A(a: String) extends Serializable
val x = sc.parallelize(Array.fill(10)(new A("hello")))
x.collect
```