Github user andrewor14 commented on the pull request:

    https://github.com/apache/spark/pull/1197#issuecomment-47140832
  
    I'd argue that (b) is also an urgent issue.
    
    Yes, for the particular case of not being able to talk to the master, an 
exception is thrown (though after a long timeout). Now consider the case in 
which you can talk to the master, but there are no workers. Then in the normal 
case, a simple Spark job leads to the following:
    ```
    >>> sc.parallelize(range(100)).count()
    14/06/25 11:26:12 INFO SparkContext: Starting job: count at <stdin>:1
    14/06/25 11:26:12 INFO DAGScheduler: Got job 0 (count at <stdin>:1) with 2 
output partitions (allowLocal=false)
    14/06/25 11:26:12 INFO DAGScheduler: Final stage: Stage 0(count at 
<stdin>:1)
    14/06/25 11:26:12 INFO DAGScheduler: Parents of final stage: List()
    14/06/25 11:26:12 INFO DAGScheduler: Missing parents: List()
    14/06/25 11:26:12 INFO DAGScheduler: Submitting Stage 0 (PythonRDD[1] at 
RDD at PythonRDD.scala:40), which has no missing parents
    14/06/25 11:26:12 INFO DAGScheduler: Submitting 2 missing tasks from Stage 
0 (PythonRDD[1] at RDD at PythonRDD.scala:40)
    14/06/25 11:26:12 INFO TaskSchedulerImpl: Adding task set 0.0 with 2 tasks
    14/06/25 11:26:27 WARN TaskSchedulerImpl: Initial job has not accepted any 
resources; check your cluster UI to ensure that workers are registered and have 
sufficient memory
    14/06/25 11:26:42 WARN TaskSchedulerImpl: Initial job has not accepted any 
resources; check your cluster UI to ensure that workers are registered and have 
sufficient memory
    14/06/25 11:26:57 WARN TaskSchedulerImpl: Initial job has not accepted any 
resources; check your cluster UI to ensure that workers are registered and have 
sufficient memory
    ...
    ```
    Now imagine all the WARN messages go away. This will continue indefinitely 
and is basically a hang. I think this is more serious than a user experience 
issue and deserves a hot fix.


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