[jira] [Commented] (MAPREDUCE-5288) ResourceEstimator#getEstimatedTotalMapOutputSize suffers from divide by zero issues

["Fengdong Yu (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAPREDUCE-5288?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13672980#comment-13672980 ] 

Fengdong Yu commented on MAPREDUCE-5288:
----------------------------------------

This was fixed in hadoop-1.1.2 stable release.
if we determine completedMapsInputSize is zero, then job's map tasks MUST be zero, so the estimated output size is zero. 
below is the code:
{code}
  long getEstimatedMapOutputSize() {
    long estimate = 0L;
    if (job.desiredMaps() > 0) {
      estimate = getEstimatedTotalMapOutputSize()  / job.desiredMaps();
    }
    return estimate;
  }
{code}
                
> ResourceEstimator#getEstimatedTotalMapOutputSize suffers from divide by zero issues
> -----------------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-5288
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5288
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: mrv1
>    Affects Versions: 1.2.0
>            Reporter: Harsh J
>            Assignee: Karthik Kambatla
>
> The computation in the above mentioned class-method is below:
> {code}
>       long estimate = Math.round(((double)inputSize * 
>           completedMapsOutputSize * 2.0)/completedMapsInputSize);
> {code}
> Given http://docs.oracle.com/javase/6/docs/api/java/lang/Math.html#round(double), its possible that the returned estimate could be Long.MAX_VALUE if completedMapsInputSize is determined to be zero.
> This can be proven with a simple code snippet:
> {code}
> class Foo {
>     public static void main(String... args) {
>         long inputSize = 600L + 2;
>         long estimate = Math.round(((double)inputSize *
>                               1L * 2.0)/0L);
>         System.out.println(estimate);
>     }
> }
> {code}
> The above conveniently prints out: {{9223372036854775807}}, which is Long.MAX_VALUE (or 8 Exbibytes per MapReduce).

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