Zero map split input length combine with none zero map split input length may cause MR1 job hung sometimes.

// TableSplit.java
public long getLength() {
    return length;
  }

// RegionSizeCalculator.java
public long getRegionSize(byte[] regionId) {
    Long size = sizeMap.get(regionId);
    if (size == null) {
      LOG.debug("Unknown region:" + Arrays.toString(regionId));
      return 0;
    } else {
      return size;
    }
  }

// findNewMapTask
    // Check to ensure this TaskTracker has enough resources to 
    // run tasks from this job
    long outSize = resourceEstimator.getEstimatedMapOutputSize();
    long availSpace = tts.getResourceStatus().getAvailableSpace();
    if(availSpace < outSize) {
      LOG.warn("No room for map task. Node " + tts.getHost() + 
               " has " + availSpace + 
               " bytes free; but we expect map to take " + outSize);

      return -1; //see if a different TIP might work better. 
    }

// in ResourceEstimator.java
protected synchronized long getEstimatedTotalMapOutputSize()  {
    if(completedMapsUpdates < threshholdToUse) {
      return 0;
    } else {
      long inputSize = job.getInputLength() + job.desiredMaps(); 
      //add desiredMaps() so that randomwriter case doesn't blow up
      //the multiplication might lead to overflow, casting it with
      //double prevents it
      long estimate = Math.round(((double)inputSize * 
          completedMapsOutputSize * 2.0)/completedMapsInputSize);
      if (LOG.isDebugEnabled()) {
        LOG.debug("estimate total map output will be " + estimate);
      }
      return estimate;
    }
  }
protected synchronized void updateWithCompletedTask(TaskStatus ts, 
      TaskInProgress tip) {

    //-1 indicates error, which we don't average in.
    if(tip.isMapTask() &&  ts.getOutputSize() != -1)  {
      completedMapsUpdates++;

      completedMapsInputSize+=(tip.getMapInputSize()+1);
      completedMapsOutputSize+=ts.getOutputSize();

      if(LOG.isDebugEnabled()) {
        LOG.debug("completedMapsUpdates:"+completedMapsUpdates+"  "+
                  "completedMapsInputSize:"+completedMapsInputSize+"  " +
                  "completedMapsOutputSize:"+completedMapsOutputSize);
      }
    }
  }