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From "Jason Lowe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-5932) Provide an option to use a dedicated reduce-side shuffle log
Date Fri, 31 Oct 2014 22:23:35 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-5932?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14192623#comment-14192623
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Jason Lowe commented on MAPREDUCE-5932:
---------------------------------------

Thanks for the patch, Gera!  I think it's a useful feature.  Apologies for the late review.

One comment on the patch: it looks like the shuffle log will always use a rolling log appender,
but syslog will sometimes be a standard log appender.  I think the appender behavior should
be consistent -- if we ask for syslog to use a rolling appender then the shuffle log should
roll as well, and if syslog is not rolling then the shuffle log shouldn't either.

> Provide an option to use a dedicated reduce-side shuffle log
> ------------------------------------------------------------
>
>                 Key: MAPREDUCE-5932
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5932
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: mrv2
>    Affects Versions: 2.4.0
>            Reporter: Gera Shegalov
>            Assignee: Gera Shegalov
>         Attachments: MAPREDUCE-5932.v01.patch, MAPREDUCE-5932.v02.patch
>
>
> For reducers in large jobs our users cannot easily spot portions of the log associated
with problems with their code. An example reducer with INFO-level logging generates ~3500
lines / ~700KiB  lines per second. 95% of the log is the client-side of the shuffle {{org.apache.hadoop.mapreduce.task.reduce.*}}
> {code}
> $ wc syslog 
>     3642   48192  691013 syslog
> $ grep task.reduce syslog | wc 
>     3424   46534  659038
> $ grep task.reduce.ShuffleScheduler syslog | wc 
>     1521   17745  251458
> $ grep task.reduce.Fetcher syslog | wc 
>     1045   15340  223683
> $ grep task.reduce.InMemoryMapOutput syslog | wc 
>      400    4800   72060
> $ grep task.reduce.MergeManagerImpl syslog | wc 
>      432    8200  106555
> {code}
> Byte percentage breakdown:
> {code}
> Shuffle total:           95%
> ShuffleScheduler:        36%
> Fetcher:                 32%
> InMemoryMapOutput:       10%
> MergeManagerImpl:        15%
> {code}
> While this is information is actually often useful for devops debugging shuffle performance
issues, the job users are often lost. 
> We propose to have a dedicated syslog.shuffle file.



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