All reduce tasks should be re-executed when tasktracker with a completed map
task failed
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Key: HADOOP-5474
URL: https://issues.apache.org/jira/browse/HADOOP-5474
Project: Hadoop Core
Issue Type: Bug
Components: mapred
Affects Versions: 0.19.0
Environment: CentOS 5,
hadoop-0.19.0
Reporter: Leitao Guo
Priority: Critical
When a tasktracker with a completed map task failed, the map task will be
re-exectuted, and all reduce tasks that haven't read the data from that
tasktracker should be re-executed. But the reduce task that have read the data
from that tasktracker will not be re-executed.
In this situation, if the outputs of multi map tasks on the same dataset are
different, for example outputting a random number, the outputs of maptask and
the re-executed maptask will probably are different. Then the re-executed
reduce tasks will read the new output of the re-executed maptask, but reduce
tasks that have read the data from the failed tasktracker have read the old
output. This probably will cause correctness of the result.
A recommended solution is that all reduce tasks should be re-executed if one
tasktracker with a completed map task failed.
Any comments? thanks!
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