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From "Mahadev konar (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-3404) Speculative Execution: speculative map tasks launched even if -Dmapreduce.map.speculative=false
Date Thu, 15 Dec 2011 07:31:30 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-3404?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13169999#comment-13169999
] 

Mahadev konar commented on MAPREDUCE-3404:
------------------------------------------

@Eric,
 How do we make sure that if mapreduce.job.maps.speculative=false and mapreduce.job.reduce.speculative=true,
the maps dont get speculated and the reduces gets speculated?
                
> Speculative Execution: speculative map tasks launched even if -Dmapreduce.map.speculative=false
> -----------------------------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-3404
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-3404
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: job submission, mrv2
>    Affects Versions: 0.23.0
>         Environment: Hadoop version is: Hadoop 0.23.0.1110031628
> 10 node test cluster
>            Reporter: patrick white
>            Assignee: Eric Payne
>            Priority: Critical
>         Attachments: MAPREDUCE-3404.1.txt
>
>
> When forcing a mapper to take significantly longer than other map tasks, speculative
map tasks are
> launched even if the mapreduce.job.maps.speculative.execution parameter is set to 'false'.
> Testcase: ran default WordCount job with spec execution set to false for both map and
reduce but still saw a fifth mapper
> task launch, ran job as follows:
> hadoop --config <config>  jar   /tmp/testphw/wordcount.jar   WordCount  
> -Dmapreduce.job.maps.speculative.execution=false  -Dmapreduce.job.reduces.speculative.execution=false

> /tmp/test_file_of_words* /tmp/file_of_words.out
> Input data was 4 text files >hdfs blocksize, with same word pattern plus one diff
text line in each file, fourth
> file was 4 times as large as others:
> hadoop --config <config>  fs -ls  /tmp
> Found 5 items
> drwxr-xr-x   - user hdfs          0 2011-10-20 16:17 /tmp/file_of_words.out
> -rw-r--r--   3 user hdfs   62800021 2011-10-20 14:45 /tmp/test_file_of_words1
> -rw-r--r--   3 user hdfs   62800024 2011-10-20 14:46 /tmp/test_file_of_words2
> -rw-r--r--   3 user hdfs   62800024 2011-10-20 14:46 /tmp/test_file_of_words3
> -rw-r--r--   3 user hdfs  271708312 2011-10-20 15:50 /tmp/test_file_of_words4
> Job launched 5 mappers despite spec exec set to false, output snippet:
>         org.apache.hadoop.mapreduce.JobCounter
>                 NUM_FAILED_MAPS=1
>                 TOTAL_LAUNCHED_MAPS=5
>                 TOTAL_LAUNCHED_REDUCES=1
>                 RACK_LOCAL_MAPS=5
>                 SLOTS_MILLIS_MAPS=273540
>                 SLOTS_MILLIS_REDUCES=212876
> Reran same case as above only set both spec exec params to 'true', same results only
this time the fifth task being
> launched is expected since spec exec = true.
> job run:
> hadoop --config <config>  jar   /tmp/testphw/wordcount.jar   WordCount  
> -Dmapreduce.job.maps.speculative.execution=true  -Dmapreduce.job.reduces.speculative.execution=true

> /tmp/test_file_of_words* /tmp/file_of_words.out
> output snippet:
>         org.apache.hadoop.mapreduce.JobCounter
>                 NUM_FAILED_MAPS=1
>                 TOTAL_LAUNCHED_MAPS=5
>                 TOTAL_LAUNCHED_REDUCES=1
>                 RACK_LOCAL_MAPS=5
>                 SLOTS_MILLIS_MAPS=279653
>                 SLOTS_MILLIS_REDUCES=211474

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