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https://issues.apache.org/jira/browse/MAPREDUCE-4772?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13492460#comment-13492460
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Robert Joseph Evans commented on MAPREDUCE-4772:
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Boy I feel dumb, I commented on the wrong JIRA and reduced its priority. The
above two comments were for MAPREDUCE-4775. Moving this one back to critical.
> Fetch failures can take way too long for a map to be restarted
> --------------------------------------------------------------
>
> Key: MAPREDUCE-4772
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4772
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: mrv2
> Affects Versions: 0.23.4
> Reporter: Robert Joseph Evans
> Assignee: Robert Joseph Evans
>
> In one particular case we saw a NM go down at just the right time, that most
> of the reducers got the output of the map tasks, but not all of them.
> The ones that failed to get the output reported to the AM rather quickly that
> they could not fetch from the NM, but because the other reducers were still
> running the AM would not relaunch the map task because there weren't more
> than 50% of the running reducers that had reported fetch failures. Then
> because of the exponential back-off for fetches on the reducers it took until
> 1 hour 45 min for the reduce tasks to hit another 10 fetch failures and
> report in again. At that point the other reducers had finished and the job
> relaunched the map task. If the reducers had still been running at 1:45 I
> have no idea how long it would have taken for each of the tasks to get to 30
> fetch failures.
> We need to trigger the map based off of percentage of reducers shuffling, not
> percentage of reducers running, we also need to have a maximum limit of the
> back off, so that we don't ever have the reducer waiting for days to try and
> fetch map output.
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