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From "Brice Arnould (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-3412) Refactor the scheduler out of the JobTracker
Date Sat, 17 May 2008 23:23:55 GMT
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
            Priority: Minor
         Attachments: JobScheduler.patch

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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