[ https://issues.apache.org/jira/browse/MAPREDUCE-4733?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Jason Lowe updated MAPREDUCE-4733: ---------------------------------- Target Version/s: 2.0.3-alpha, 0.23.5 Status: Patch Available (was: Open) > 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 > > > 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. -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators For more information on JIRA, see: http://www.atlassian.com/software/jira