Occasionally when running jobs, Hadoop fails to clean up the
"_temporary" directories it has left behind. This only appears to
happen when a task is killed (aka a speculative execution), and the
data that task has outputted so far is not cleaned up. Is this a known
issue in hadoop? Is the data from that task guaranteed to be duplicate
data of what was outputted by another task? Is it safe to just delete
this directory without worrying about losing data?