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From "Devaraj Das (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3412) Refactor the scheduler out of the JobTracker
Date Mon, 14 Jul 2008 12:27:33 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3412?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12613307#action_12613307
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Devaraj Das commented on HADOOP-3412:
-------------------------------------

bq. I  think this is good to have in the scheduler. It is easy to default the implementation
to return only 1 task as it does today. But leaves the options open with we get to HADOOP-3136.
Should we get this in ?

Makes sense

Regarding the padding, i am thinking that it makes sense to not have it at all. In general,
we *must* execute failed tasks first always. This will ensure that jobs with deterministic
task failures fail really early in the game. But this is more of a change in the JobInProgress
class. Regarding speculative tasks the obtainNewMapTask/obtainNewReduceTask could return a
speculative task if they desire so. And this logic better be in the JobInProgress class that
has all the tasks' information.

> Refactor the scheduler out of the JobTracker
> --------------------------------------------
>
>                 Key: HADOOP-3412
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3412
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: mapred
>            Reporter: Brice Arnould
>            Assignee: Brice Arnould
>            Priority: Minor
>             Fix For: 0.19.0
>
>         Attachments: JobScheduler-v9.1.patch, JobScheduler-v9.2.patch, JobScheduler-v9.patch,
JobScheduler.patch, JobScheduler_v2.patch, JobScheduler_v3.patch, JobScheduler_v3b.patch,
JobScheduler_v4.patch, JobScheduler_v5.patch, JobScheduler_v6.1.patch, JobScheduler_v6.2.patch,
JobScheduler_v6.3.patch, JobScheduler_v6.4.patch, JobScheduler_v6.patch, JobScheduler_v7.1.patch,
JobScheduler_v7.patch, JobScheduler_v8.patch, RackAwareJobScheduler.java, SimpleResourceAwareJobScheduler.java
>
>
> First I would like warn you that my proposition is assumed to be very naive. I just hope
that reading it won't make you lose time.
> h4. The aim
> It seems to me that improving Hadoop scheduling could be very profitable. But, it is
hard to implement and compare schedulers, because the scheduling logic is mixed within the
rest of the JobTracker.
> This bug is the first step of an attempt to improve the Hadoop scheduler. It re-implements
the current scheduling algorithm in a separate class called JobScheduler. This new class is
instantiated in the JobTracker.
> h4. Bug fixed as a side effects
> This patch probably cannot be submited as it is.
> A first difficulty is that it does not have exactly the same behaviour than the current
JobTracker. More precisely, it doesn't re-implement things like code that seems to be never
called or concurency problems.
> I wrote TOCONFIRM where my proposition differ from the current implementation, so you
can find them easily.
> I know that fixing bugs silently is bad. So, independently of what you decide about this
patch, I will open issues for bugs that you confirm.
> h4. Other side effects
> Another side effect of this patch is to add documentation about each step of the scheduling.
I hope that it will help future improvement by lowering the level required to contribute to
the scheduler.
> It also reduces the complexity and the granularity of the JobTracker (making it more
parallel).
> h4. The future
> If you feel that this is a step the right direction, I will try to propose a JobSchedulerInterface
that many JobSchedulers could implement and to propose alternatives to the current « FifoJobScheduler
».  If some of you have ideas about that please tell ^^ I will also open issues for things
marked as FIXME in the patch.

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