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https://issues.apache.org/jira/browse/HADOOP-1699?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12518600
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Arun C Murthy commented on HADOOP-1699:
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Please take a look at the config knob {{mapred.child.java.opts}}:
{noformat}
<property>
<name>mapred.child.java.opts</name>
<value>-Xmx200m</value>
<description>Java opts for the task tracker child processes. Subsumes
'mapred.child.heap.size' (If a mapred.child.heap.size value is found
in a configuration, its maximum heap size will be used and a warning
emitted that heap.size has been deprecated). Also, the following symbols,
if present, will be interpolated: @taskid@ is replaced by current TaskID;
and @port@ will be replaced by mapred.task.tracker.report.port + 1 (A second
child will fail with a port-in-use if mapred.tasktracker.tasks.maximum is
greater than one). Any other occurrences of '@' will go unchanged. For
example, to enable verbose gc logging to a file named for the taskid in
/tmp and to set the heap maximum to be a gigabyte, pass a 'value' of:
-Xmx1024m -verbose:gc -Xloggc:/tmp/@[EMAIL PROTECTED]
</description>
</property>
{noformat}
I'm inclined to resolve this bug as *Invalid* since it already is supported...
agree?
> 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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