protected void checkIsClosed() throws StreamingException {
    if (isTxnClosed.get()) {
      throw new StreamingException("Transaction" + toString() + " is closed()");
    }
  }
once any operation on this batch encounters a system exception
(e.g. IOException on write) it's safest to assume that we can't write to the
file backing this batch any more.  This guards important public methods
streaming/src/java/org/apache/hive/streaming/AbstractStreamingTransaction.java