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From Iván de Prado (JIRA) <j...@apache.org>
Subject [jira] Created: (HADOOP-3420) Recover the deprecated mapred.tasktracker.tasks.maximum
Date Tue, 20 May 2008 12:18:55 GMT
Recover the deprecated mapred.tasktracker.tasks.maximum
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                 Key: HADOOP-3420
                 URL: https://issues.apache.org/jira/browse/HADOOP-3420
             Project: Hadoop Core
          Issue Type: Improvement
          Components: conf
    Affects Versions: 0.16.4, 0.16.3, 0.16.2, 0.16.1, 0.16.0
            Reporter: Iván de Prado


https://issues.apache.org/jira/browse/HADOOP-1274 replaced the configuration attribute mapred.tasktracker.tasks.maximum
with mapred.tasktracker.map.tasks.maximum and mapred.tasktracker.reduce.tasks.maximum because
it sometimes make sense to have more mappers than reducers assigned to each node.

But deprecating mapred.tasktracker.tasks.maximum could be an issue in some situations. For
example, when more than one job is running, reduce tasks + map tasks eat too many resources.
For avoid this cases an upper limit of tasks is needed. So I propose to have the configuration
parameter mapred.tasktracker.tasks.maximum as a total limit of task. It is compatible with
mapred.tasktracker.map.tasks.maximum and mapred.tasktracker.reduce.tasks.maximum.

As an example:

I have a 8 cores, 4GB, 4 nodes cluster. I want to limit the number of tasks per node to 8.
8 tasks per nodes would use almost 100% cpu and 4 GB of the memory. I have set:
  mapred.tasktracker.map.tasks.maximum -> 8
  mapred.tasktracker.reduce.tasks.maximum -> 8 

1) When running only one Job at the same time, it works smoothly: 8 task average per node,
no swapping in nodes, almost 4 GB of memory usage and 100% of CPU usage. 

2) When running more than one Job at the same time, it works really bad: 16 tasks average
per node, 8 GB usage of memory (4 GB swapped), and a lot of System CPU usage.

So, I think that have sense to restore the old attribute mapred.tasktracker.tasks.maximum
making it compatible with the new ones.

Task trackers could not:
 - run more than mapred.tasktracker.tasks.maximum tasks per node,
 - run more than mapred.tasktracker.map.tasks.maximum mappers per node, 
 - run more than mapred.tasktracker.reduce.tasks.maximum reducers per node. 

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