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From "Amar Kamat (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 05:54:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4472?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12642062#action_12642062
] 

Amar Kamat commented on HADOOP-4472:
------------------------------------

+1

> 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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