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https://issues.apache.org/jira/browse/MAPREDUCE-6076?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14289763#comment-14289763
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Ray Chiang commented on MAPREDUCE-6076:
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+1 (non-binding). Code looks fine to me and the test passes in my tree.
> 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
> Attachments: MAPREDUCE-6076.branch-1.000.patch
>
>
> 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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