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From "Andy Konwinski (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3412) Refactor the scheduler out of the JobTracker
Date Fri, 06 Jun 2008 23:24:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3412?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12603226#action_12603226
] 

Andy Konwinski commented on HADOOP-3412:
----------------------------------------

I don't think that in java 1.5 the @override annotation is supported for use with methods
which are defined in an interface which the class implements. It seems that this behavior
is supported in java 1.6, but in 1.5 @override is supposed to be used only when you override
a method that is defined in your superclass. Thus when i run ant with this patch applied,
i get errors. Everything still needs to compile with 1.5 as of now, so I guess we should remove
these @override annotations.

> 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.patch,
RackAwareJobScheduler.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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