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