[jira] [Created] (MAPREDUCE-5932) Provide an option to use a dedicated reduce-side shuffle log

[Gera Shegalov (JIRA)]

Gera Shegalov created MAPREDUCE-5932:
----------------------------------------

             Summary: 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


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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