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https://issues.apache.org/jira/browse/MAPREDUCE-1881?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12896181#action_12896181
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Matei Zaharia commented on MAPREDUCE-1881:
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The point of this change is to allow the user to specify a comma-separated list
of classes in the job.tracker.instrumentation field instead of a single class.
Asking users to specify the composite class, and then go set another property
somewhere else, is needlessly inconvenient. What is the problem with the
current approach? If the user only specifies one instrumentation class (as they
do today), only that one class will be used, and the behavior will be exactly
the same as today (except that calls get routed through the composite object
first). If the user lists multiple classes, multiple classes will be used.
> Improve TaskTrackerInstrumentation
> ----------------------------------
>
> Key: MAPREDUCE-1881
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-1881
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Reporter: Matei Zaharia
> Assignee: Matei Zaharia
> Priority: Minor
> Attachments: mapreduce-1881-v2.patch, mapreduce-1881.patch
>
>
> The TaskTrackerInstrumentation class provides a useful way to capture key
> events at the TaskTracker for use in various reporting tools, but it is
> currently rather limited, because only one TaskTrackerInstrumentation can be
> added to a given TaskTracker and this objects receives minimal information
> about tasks (only their IDs). I propose enhancing the functionality through
> two changes:
> # Support a comma-separated list of TaskTrackerInstrumentation classes rather
> than just a single one in the JobConf, and report events to all of them.
> # Make the reportTaskLaunch and reportTaskEnd methods in
> TaskTrackerInstrumentation receive a reference to a whole Task object rather
> than just its TaskAttemptID. It might also be useful to make the latter
> receive the task's final state, i.e. failed, killed, or successful.
> I'm just posting this here to get a sense of whether this is a good idea. If
> people think it's okay, I will make a patch against trunk that implements
> these changes.
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