apache/incubator-spark — pull request #359 by ScrapCodes (2014-01-08 11:05:48+00:00)
Title: We clone hadoop key and values by default and reuse objects if asked to.

We try to clone for most common types of writables and we call WritableUtils.clone otherwise intention is to optimize, for example for NullWritable there is no need and for Long, int and String creating a new object with value set would be faster than doing copy on object hopefully.