title: spark 1.6.3 stuck when union rdd
body: <p>I want union two RDDs, one from RDBMS and one from hdfs.</p>
  
  <p>It work fine when the hdfs file was not exists. And when it's exists, and union the two RDDs. Spark will stuck.</p>
  
  <p>the log:</p>
  
  <pre><code>16/11/24 20:01:29 INFO ShuffleBlockFetcherIterator: Getting 2 non-empty blocks out of 200 blocks
  16/11/24 20:01:29 INFO ShuffleBlockFetcherIterator: Started 0 remote fetches in 1 ms
  16/11/24 20:01:29 INFO ShuffleBlockFetcherIterator: Getting 1 non-empty blocks out of 1 blocks
  16/11/24 20:01:29 INFO ShuffleBlockFetcherIterator: Started 0 remote fetches in 0 ms
  16/11/24 20:01:29 INFO Executor: Finished task 2.0 in stage 5.0 (TID 409). 2074 bytes result sent to driver
  16/11/24 20:01:29 INFO TaskSetManager: Finished task 2.0 in stage 5.0 (TID 409) in 76 ms on localhost (1/3)
  </code></pre>
  
  <p>stop at here.</p>
  
  <p>the code:</p>
  
  <pre><code>val allUserAction = if (exists) {
    val textFile = sc.textFile(historyHDFSFilePath).map { line =&gt;
    //val textFile = sc.textFile("file:///Volumes/disk02/Desktop/part-00000").map { line =&gt;
      val values = line.split(",")
      if (values.length == 13) {
        (values(0).toLong, (values(1), values(2).toLong, values(3).toLong,
          values(4).toInt, values(5).toLong, values(6).toInt, values(7).toBoolean, false, values(8).toBoolean,
          values(9).toBoolean, values(10).toBoolean, values(11).toInt, values(12).toInt))
      } else {
        (0L, ("", 0L, 0L, 0, 0L, 0, false, false, false, false, false, 0, 0))
      }
    }
    textFile.union(registerUserSourceWithOp)
  } else {
    registerUserSourceWithOp
  }.cache()
  
  allUserAction.collect().foreach(println)
  </code></pre>
  
  <p>If I copy the file from hdfs to local machine. and read from it. it work fine.
  How to fix it. THX~</p>