apache/incubator-spark — pull request #220 by rxin (2013-12-01 02:11:56+00:00)
Title: Memoize preferred locations in ZippedPartitionsBaseRDD

so preferred location computation doesn't lead to exponential explosion.

This was a problem in GraphX where we have a whole chain of RDDs that are ZippedPartitionsRDD's, and the preferred locations were taking eternity to compute.

(cherry picked from commit e36fe55a031d2c01c9d7c5d85965951c681a0c74)
Signed-off-by: Reynold Xin