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From "Hemanth Yamijala (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4472) Should we move out the creation of setup/cleanup tasks from JobInProgress.initTasks()?
Date Thu, 23 Oct 2008 06:32:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4472?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12642076#action_12642076
] 

Hemanth Yamijala commented on HADOOP-4472:
------------------------------------------

As an update, I had a discussion with Owen, and we think it is better to make the schedulers
explicitly aware of setup tasks. However, we do need consensus and more thought on this. And
more importantly, it might be a very big change if we want this fixed for Hadoop 0.19.1. So
for the interim, the option proposed here will suffice.

Also note that the separation of setup / cleanup from initTasks makes sense even if we make
the schedulers aware of the tasks. The discussion is only about the jobAdded part that I have
proposed before.

> 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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