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https://issues.apache.org/jira/browse/HADOOP-3412?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12614382#action_12614382
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Vivek Ratan commented on HADOOP-3412:
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Tom, nice work. It certainly makes the hierarchy cleaner. It also cleanly
separates out the differences between listening for changes and supporting a
scheduler API.
Another of my concerns (being able to share code/functionality among
schedulers) is still not resolved, but it may be a nice-to-have feature, and
will probably have a solution different from what we're discussing here, so
perhaps that discussion can be on a separate Jira. To reiterate that concern:
suppose I want a scheduler that limits tasks per job (so I'd like to reuse code
from LimitTasksPerJobTaskScheduler, including the code that deals with
configuration). Suppose I also want my scheduler to implement some fair-share
functionality that some class, FairShareScheduler has defined (this could be a
class similar to that proposed in HADOOP-3746). I'd like to reuse code from
that class too. Maybe I also want some feature (per user limits, for example)
that exists in the scheduler for 3445. How do I do that? Again, this may be
something we do in the future. I don't think it affects the design of
JobInProgressListener and TaskScheduler, so we can discuss it elsewhere at the
appropriate time.
> 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-v10.patch, JobScheduler-v11.patch,
> JobScheduler-v12.patch, 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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