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From "patrick white (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAPREDUCE-3404) Speculative Execution: speculative map tasks launched even if -Dmapreduce.job.maps.speculative.execution=false
Date Tue, 15 Nov 2011 19:18:52 GMT
Speculative Execution: speculative map tasks launched even if -Dmapreduce.job.maps.speculative.execution=false
--------------------------------------------------------------------------------------------------------------

                 Key: MAPREDUCE-3404
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-3404
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: job submission
    Affects Versions: 0.23.0
         Environment: Hadoop version is: Hadoop 0.23.0.1110031628
10 node test cluster

            Reporter: patrick white


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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