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From "Srikanth Kakani (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1699) Child task debugging on Hadoop
Date Thu, 09 Aug 2007 18:27:42 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1699?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12518794

Srikanth Kakani commented on HADOOP-1699:

Yes I agree. It would be invalid in that case. Also is there any documentation regarding child
process debugging? Maybe we should add it in there. It took me a long time to figure it out.
I wish someone gets use out of the effort.

> Child task debugging on Hadoop
> ------------------------------
>                 Key: HADOOP-1699
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1699
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: mapred
>         Environment: Any hadoop installation
>            Reporter: Srikanth Kakani
>            Priority: Critical
> Recently I discovered debugging a map/reduce task on hadoop can be simplified with couple
of lines code in TaskRunner enabling us to run jdb on the child tasks.
> TaskRunner.java: 282
>         if(conf.getBoolean("mapred.debug.child.task", false)) {
>             Random r=new Random();
>             int debugPort=8000 + r.nextInt(1000);
>             vargs.add("-Xdebug");
>             vargs.add("-Xrunjdwp:transport=dt_socket,address="+ debugPort +",server=y,suspend=n");
>             LOG.info("Running debug server for task "+ t.getTaskId() + " at port" + debugPort);
>         }
> This code runs the child tasks with debug enabled after getting a configuration variable.
> Connecting to a child task is as simple as running jdb -attach <hostname>:<debugPort>
from anywhere. Additionally authentication information could be included in the jobConf. 
> I believe it will greatly reduce the development/debug time on hadoop.

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