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From "Brice Arnould (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3412) Refactor the scheduler out of the JobTracker
Date Tue, 01 Jul 2008 12:23:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3412?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12609543#action_12609543
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Brice Arnould commented on HADOOP-3412:
---------------------------------------

Thanks for your very detailed answer.
I have nothing about adding a superclass, if it is needed. I think that this class would look
like the JobScheduler of v6.4 .

However, I'm unsure about whether I understand your use case or not.
If I understand, you want to write a scheduler that have two functionalities :
* limiting the maximum number of task running per user
* providing per-user jobqueues

If my understanding is correct, those two functionalities are independent and should not be
glued in a single class (eg. you might want to limit the number of per-user tasks even if
the JobQueue is a simple Fifo). However, you would benefit of the JobFilter discussed above
to ease the implementation of your TaskScheduler. (It's also true that if the jobqueue is
a roundrobin between users, an optimized JobFilter could be written)

Do you have a draft of the scheduler you're talking about (implemented for example on top
of v6.4) ?
If so, I would like to see it, so I'll port it to both API and see what it looks like on them.

Thanks for your patience, but I want to be sure that I understand the problem
Brice

> 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.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, 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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