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https://issues.apache.org/jira/browse/MAPREDUCE-4733?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13480298#comment-13480298
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Hadoop QA commented on MAPREDUCE-4733:
--------------------------------------
{color:green}+1 overall{color}. Here are the results of testing the latest
attachment
http://issues.apache.org/jira/secure/attachment/12550053/MAPREDUCE-4733.patch
against trunk revision .
{color:green}+1 @author{color}. The patch does not contain any @author
tags.
{color:green}+1 tests included{color}. The patch appears to include 5 new
or modified test files.
{color:green}+1 javac{color}. The applied patch does not increase the
total number of javac compiler warnings.
{color:green}+1 javadoc{color}. The javadoc tool did not generate any
warning messages.
{color:green}+1 eclipse:eclipse{color}. The patch built with
eclipse:eclipse.
{color:green}+1 findbugs{color}. The patch does not introduce any new
Findbugs (version 1.3.9) warnings.
{color:green}+1 release audit{color}. The applied patch does not increase
the total number of release audit warnings.
{color:green}+1 core tests{color}. The patch passed unit tests in
hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app
hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-hs.
{color:green}+1 contrib tests{color}. The patch passed contrib unit tests.
Test results:
https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/2948//testReport/
Console output:
https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/2948//console
This message is automatically generated.
> Reducer can fail to make progress during shuffle if too many reducers
> complete consecutively
> --------------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-4733
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4733
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: applicationmaster, mrv2
> Affects Versions: 0.23.3
> Reporter: Jason Lowe
> Assignee: Jason Lowe
> Attachments: MAPREDUCE-4733.patch, MAPREDUCE-4733.patch,
> MAPREDUCE-4733.patch
>
>
> TaskAttemptListenerImpl implements getMapCompletionEvents by calling
> Job.getTaskAttemptCompletionEvents with the same fromEvent and maxEvents
> passed in from the reducer and then filtering the result for just map events.
> We can't filter the task completion event list and expect the caller's
> "window" into the list to match up. As soon as a reducer event appears in
> the list it means we are redundantly sending map completion events that were
> already seen by the reducer.
> Worst case the reducer will hang if all of the events in the requested window
> are reducer events. In that case zero events will be reported back to the
> caller and it won't bump up fromEvent on the next call. Reducer then never
> sees the final map completion events needed to complete the shuffle. This
> could happen in a case where all maps complete, more than MAX_EVENTS reducers
> complete consecutively, but some straggling reducers get fetch failures and
> cause a map to be restarted.
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