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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-4772) Fetch failures can take way too long for a map to be restarted
Date Wed, 07 Nov 2012 19:30:14 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-4772?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13492620#comment-13492620
] 

Hadoop QA commented on MAPREDUCE-4772:
--------------------------------------

{color:red}-1 overall{color}.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12552513/MR-4772-trunk.txt
  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 2 new or modified
test files.

      {color:red}-1 javac{color}.  The applied patch generated 2031 javac compiler warnings
(more than the trunk's current 2025 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-core.

    {color:green}+1 contrib tests{color}.  The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/2993//testReport/
Javac warnings: https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/2993//artifact/trunk/patchprocess/diffJavacWarnings.txt
Console output: https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/2993//console

This message is automatically generated.
                
> 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
>            Priority: Critical
>         Attachments: MR-4772-0.23.txt, MR-4772-trunk.txt
>
>
> 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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