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