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https://issues.apache.org/jira/browse/HADOOP-3412?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12612963#action_12612963
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Tom White commented on HADOOP-3412:
-----------------------------------
{quote}
@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.
{quote}
Java 6 is required now. See HADOOP-2325.
{quote}
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).
{quote}
Yes, I mentioned this above. I'm not comfortable with just making all of these
classes public without thinking through the interfaces, since we have to
maintain these public interfaces, and be careful (and backwards compatible)
with evolution. So I suggest we keep them package private for the first
release, and figure how to open it up later.
I'd be interested to hear others' thoughts about this.
> 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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