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https://issues.apache.org/jira/browse/MAPREDUCE-1881?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12897114#action_12897114
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Matei Zaharia commented on MAPREDUCE-1881:
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By necessity, do you mean "why should Hadoop provide this feature rather than
letting users implement it themselves"? The answer is pretty simple -- since
many users will want to do the same thing, it makes sense to put it into the
platform instead of asking them all to reinvent it. The goal of the JIRA
process is not to minimize changes to Hadoop, it's to make Hadoop better. One
can imagine many useful instrumentation classes being written that people will
combine (already, lots of people are using the default metrics one).
I actually opened this issue because I'm working on a project where I want to
programmatically launch a TaskTracker with an extra instrumentation class on
top of the ones the user configured in mapred-site.xml. I could do it by
setting the parameter to a composite class, and then passing it the old
parameter, but it felt more natural to add support for multiple instrumentation
objects and just append to the user's list. I care more about the second part
of the issue (statusUpdate callback) though, because my project can't work at
all without that.
> 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-v2b.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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