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From "Matei Zaharia (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3412) Refactor the scheduler out of the JobTracker
Date Fri, 11 Jul 2008 18:46:32 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3412?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12612955#action_12612955
] 

Matei Zaharia commented on HADOOP-3412:
---------------------------------------

Tom - I ran into a few issues applying your 9.1 patch, which I've fixed in a new patch (9.2):
- @Override was being used in TaskTracker on methods from the interface Configurable, which
is not allowed in Java 1.5. Java 1.5 only lets you use @Override on methods overridden from
a class.
- TaskTrackerManager.taskTrackers() returned a Collection with no type parameters. I changed
this to Collection<TaskTrackerStatus>.
- Several classes used by the scheduler API had package-only visibility in org.apache.hadoop.mapred,
which is problematic for anyone writing a scheduler outside this package. It makes sense to
allow schedulers to be in different packages to prevent namespace pollution. I changed the
visibility of several types to public (JobInProgress, Task, TaskInProgress, TaskTrackerStatus,
TaskTrackerManager). I also made JobInProgress.getConf() public since the conf will often
be used to put per-job scheduling parameters (such as queue name).

> 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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