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From "Bhallamudi Venkata Siva Kamesh (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-2637) Providing options to debug the mapreduce user code (Mapper, Reducer, Combiner, Sort implementations)
Date Tue, 12 Jul 2011 06:50:00 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-2637?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13063746#comment-13063746
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Bhallamudi Venkata Siva Kamesh commented on MAPREDUCE-2637:
-----------------------------------------------------------

We choose a base port. 
1) If the task type is map task, *basePort + MapTaskId* will be the debug port for map task.
2) If the task type is reduce task, *basePort - ReduceTaskId* will be the debug port for reduce
task.

There will be no port conflict issues, even a reduce task is started while a map task is still
in progress.
But this is possible, only when a particular range of ports are free.

> Providing options to debug the mapreduce user code (Mapper, Reducer, Combiner, Sort implementations)
> ----------------------------------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-2637
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2637
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: tasktracker
>            Reporter: Devaraj K
>            Assignee: Devaraj K
>
> Presently Hadoop provides "mapred.child.java.opts" configuration which can be used to
set JVM options for Child JVM running Map or Reduce Task. 
> If we need to remote debug the Child JVM, we can add remote debugging options to this
configuration value.
> But this will work only for single Child JVM. Other children will fail as the remote
debugging port is already used.
> We cannot specify the remote debugging port dynamically.
> As a result, it's not possible to remote debug multiple Child JVMs.
> As a solution to this problem, we can provide a configuration to debug Task JVMs in this
scenario.

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