Hadoop Map/Reduce
  1. Hadoop Map/Reduce
  2. MAPREDUCE-3404

Speculative Execution: speculative map tasks launched even if -Dmapreduce.map.speculative=false

    Details

    • Type: Bug Bug
    • Status: Closed
    • Priority: Critical Critical
    • Resolution: Fixed
    • Affects Version/s: 0.23.0
    • Fix Version/s: 0.23.1
    • Component/s: job submission, mrv2
    • Labels:
      None
    • Environment:

      Hadoop version is: Hadoop 0.23.0.1110031628
      10 node test cluster

    • Hadoop Flags:
      Reviewed
    • Release Note:
      Corrected MR AM to honor speculative configuration and enable speculating either maps or reduces.

      Description

      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-rr- 3 user hdfs 62800021 2011-10-20 14:45 /tmp/test_file_of_words1
      rw-rr- 3 user hdfs 62800024 2011-10-20 14:46 /tmp/test_file_of_words2
      rw-rr- 3 user hdfs 62800024 2011-10-20 14:46 /tmp/test_file_of_words3
      rw-rr- 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

      1. MAPREDUCE-3404.2.txt
        14 kB
        Eric Payne
      2. MAPREDUCE-3404.1.txt
        11 kB
        Eric Payne

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          People

          • Assignee:
            Eric Payne
            Reporter:
            patrick white
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            Dates

            • Created:
              Updated:
              Resolved:

              Development