I've got a PR up to completely remove the v2 commit algorithm https://github.com/apache/hadoop/pull/2320
That may seem overkill, but while *we* know there's a small window of risk (task attempt 1 failing partway through a nonatomic commit), that's not known/appreciated by others. The patch removes the v2 codepath from FileOutputCommitter, making it a lot less complicated, and when v2 is requested, a warning is printed and the option ignored. Overkill? Maybe. But it guarantees correctness
