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From "Gera Shegalov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-5932) Provide an option to use a dedicated reduce-side shuffle log
Date Wed, 26 Nov 2014 07:53:12 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-5932?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14225873#comment-14225873
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Gera Shegalov commented on MAPREDUCE-5932:
------------------------------------------

I believe failures are unrelated. I reran the 2 tests on my laptop without any issues. [~jlowe],
can you take a look at this version please?

> 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, MAPREDUCE-5932.v03.patch,
MAPREDUCE-5932.v04.patch, MAPREDUCE-5932.v05.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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