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From Lin Ma <lin...@gmail.com>
Subject Re: Fair Scheduler of Hadoop
Date Sat, 26 Jan 2013 15:38:19 GMT
Thanks Joep, smart answer! All of my confusions are gone. Have a good


On Tue, Jan 22, 2013 at 2:00 AM, Joep Rottinghuis <jrottinghuis@gmail.com>wrote:

> You could configure it like that if you wanted. Keep in mind that would
> waste some resources. Imagine a 10 minute task that has been running for 9
> minutes. If you have that task killed immediately then it would have to be
> the-scheduled and re-do all 10 minutes.
> Give it another minute and the task is complete and out if the way.
> So, consider how busy your cluster is overall and how much you are willing
> to wait for fairness trading this off against a certain amount of waste.
> Cheers,
> Joep
> Sent from my iPhone
> On Jan 21, 2013, at 9:30 AM, Lin Ma <linlma@gmail.com> wrote:
> Hi Joep,
> Excellent answer! I think you have answered my confusions. And one
> remaining issue after reading this document again, even it is old. :-)
> It is mentioned, "which will allow you to set how long each pool will
> wait before preempting other jobs’ tasks to reach its guaranteed capacity",
> my question is why each pool need wait here? If a pool cannot get its
> guaranteed capacity because of jobs in other pools over use the capacity,
> we should kill such jobs immediately? Appreciate if you could elaborate a
> bit more why we need wait to get even guaranteed capacity.
> regards,
> Lin
> On Mon, Jan 21, 2013 at 8:24 AM, Joep Rottinghuis <jrottinghuis@gmail.com>wrote:
>> Lin,
>> The article you are reading us old.
>> Fair scheduler does have preemption.
>> Tasks get killed and rerun later, potentially on a different node.
>> You can set a minimum / guaranteed capacity. The sum of those across
>> pools would typically equal the total capacity of your cluster or less.
>> Then you can configure each pool to go beyond that capacity. That would
>> happen if the cluster is temporary not used to the full capacity.
>> Then when the demand for capacity increases, and jobs are queued in other
>> pools that are not running at their minimum guaranteed capacity, some long
>> running tasks from jobs in the pool that is using more than its minimum
>> capacity get killed (to be run later again).
>> Does that make sense?
>> Cheers,
>> Joep
>> Sent from my iPhone
>> On Jan 20, 2013, at 6:25 AM, Lin Ma <linlma@gmail.com> wrote:
>> Hi guys,
>> I have a quick question regarding to fire scheduler of Hadoop, I am
>> reading this article =>
>> http://blog.cloudera.com/blog/2008/11/job-scheduling-in-hadoop/, my
>> question is from the following statements, "There is currently no
>> support for preemption of long tasks, but this is being added in
>> HADOOP-4665 <https://issues.apache.org/jira/browse/HADOOP-4665>, which
>> will allow you to set how long each pool will wait before preempting other
>> jobs’ tasks to reach its guaranteed capacity.".
>> My questions are,
>> 1. What means "preemption of long tasks"? Kill long running tasks, or
>> pause long running tasks to give resources to other tasks, or it means
>> something else?
>> 2. I am also confused about "set how long each pool will wait before
>> preempting other jobs’ tasks to reach its guaranteed capacity"., what
>> means "reach its guaranteed capacity"? I think when using fair
>> scheduler, each pool has predefined resources allocation settings (and the
>> settings guarantees each pool has resources as configured), is that true?
>> In what situations each pool will not have its guaranteed (or configured)
>> capacity?
>> regards,
>> Lin

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