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https://issues.apache.org/jira/browse/HADOOP-3412?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Tom White updated HADOOP-3412:
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Attachment: JobScheduler-v11.patch
For this issue, which is about moving scheduling logic from the JobTracker to a
scheduler class, I think we can leave out queues. We don't currently have the
explicit concept of a queue, so I think it makes sense to commit this change,
and continue the discussion about adding queues in HADOOP-3445. As discussed
earlier, this Jira will not change the public APIs yet, so we can go on
evolving the scheduling interface.
bq. Fair point about the JobInProgress being fine for the API, provided that
the scheduler is required to call initTasks on the JobInProgress when it should
be loaded.
The implication of this is that the Scheduler takes over the responsibility of
managing the jobInitQueue. I've created a patch which does this (v11) by
inserting a EagerTaskInitializationTaskScheduler into the TaskScheduler
hierarchy. In doing so I needed a couple of lifecycle methods, which I've named
following HADOOP-3628, so TaskScheduler can be retrofitted to extend Service
after HADOOP-3628 is committed.
Does this look OK?
bq. an event when a TIP changes state, so that the scheduler can update its
data structures
Would the taskUpdated method be called by JobTracker#updateTaskStatuses? I can
see that it might be useful for schedulers to have this information, but
perhaps this is something to add to the interface when a use case comes up?
(TaskScheduler is an abstract class, so it's easy to add new methods to it.)
> 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-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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