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https://issues.apache.org/jira/browse/HADOOP-4472?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12641801#action_12641801
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Devaraj Das commented on HADOOP-4472:
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+1. As we discussed offline, i think it makes sense to not initialize all tasks
of a job before its setupTask completes. And yes, earlier the JobClient used to
run setup for the job and purely from that point of view, it doesn't seem too
bad to order jobs in a Scheduler's WaitingQueue in the order of the setupTask
completions. What do others think?
> Should we move out the creation of setup/cleanup tasks from
> JobInProgress.initTasks()?
> ---------------------------------------------------------------------------------------
>
> Key: HADOOP-4472
> URL: https://issues.apache.org/jira/browse/HADOOP-4472
> Project: Hadoop Core
> Issue Type: Improvement
> Components: mapred
> Reporter: Vivek Ratan
>
> JobInProgress.initTasks() creates TIPs for map and reduce tasks, and also the
> newly-introduced setup and cleanup tasks. initTasks() is called by the
> schedulers, as for reasons of memory optimizations, schedulers may choose to
> initialize M/R tasks at various moments (the Capacity Scheduler, for example,
> calls initTasks() just when it considers a job for running). One can say that
> Schedulers 'own' the initialization of M/R tasks in a job. Furthermore the JT
> 'owns' the setup and cleanup tasks (it schedules them, and Schedulers are
> unaware of these tasks). This causes a problematic dependency between the JT
> and a Scheduler. For example, the Capacity Scheduler calls initTasks() and
> immediately calls JobInProgress.obtainNewMapTask for a map task. This is a
> problem today, because we cannot run any map or reduce tasks before the setup
> task is run, which the Capacity Scheduler is not aware of.
> Either all Schedulers are explicitly aware of setup/cleanup tasks and their
> dependencies with M/R tasks (in which case, Schedulers 'own' the creation and
> scheduling of all these tasks correctly), or the JT 'owns' the setup/cleanup
> tasks and Schedulers are completely unaware of them (in which case, the
> creation of setup/cleanup tasks must be moved out of initTasks into a
> separate method which is called by the JT).
> I think the latter is the right way to go (unless we implement HADOOP-4421,
> in which case the former option may be viable as well).
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