[jira] [Created] (MAPREDUCE-6076) Zero map split input length combine with none zero map split input length will cause MR1 job hung.

[zhihai xu (JIRA)]

zhihai xu created MAPREDUCE-6076:
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             Summary: Zero map split input length combine with none zero  map 
split input length will cause MR1 job hung. 
                 Key: MAPREDUCE-6076
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-6076
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: mrv1
            Reporter: zhihai xu
            Assignee: zhihai xu


Zero map split input length combine with none zero map split input length will 
cause MR1 job hung. 
This problem may happen when use HBASE input split(TableSplit).
HBASE split input length can be zero for unknown regions or non-zero for known 
regions in the following code:
{code}
// 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;
    }
  }
{code}
The TableSplit length come from RegionSizeCalculator.getRegionSize.

The job hung is because in MR1,
If these zero split input length map tasks are scheduled and completed before 
all none zero split input length map tasks are scheduled,
Scheduling new map task in JobProgress.java will be failed to pass the 
TaskTracker resources check at.
{code}
// 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. 
    }
{code}
The resource calculation is at
{code}
// 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);
      }
    }
  }
{code}
You can see in the calculation:
completedMapsInputSize will be a very small number and inputSize * 
          completedMapsOutputSize  will be a very big number
For example, completedMapsInputSize = 1; inputSize = 100MBytes and  
completedMapsOutputSize=100MBytes,
The estimate will be 5000TB which will be more than most task tracker disk 
space size.

So I think if the map split input length is 0, it means the split input length 
is unknown and it is reasonable to use map output size as input size for the 
calculation in ResourceEstimator. I will upload a fix based on this method.



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