mesos/spark — pull request #647 by jerryshao (2013-06-13 02:54:09+00:00)
Title: Reduce ZippedPartitionsRDD's getPreferredLocations complexity from O(2^2n) to O(2^n)

ZippedPartitionsRDD's `getPreferredLocations()` complexity is now O(2^2n), which will become a efficiency problem when running iterative job or streaming job that uses previous calculated RDD, for example:

```
var zipRdd = ...
for (i <- 1 to 100)
val newRdd = ...
zipRdd = zipRdd.zipPartitions(f, newRdd)
}
```

This patch reduce complexity from O(2^2n) to originally O(2^n) while keep algorithm the same as before.