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Date: Fri, 7 Dec 2012 14:51:26 -0500
Message-ID: 
 <CAPQV63VE=1aDdXY5g52Tfv2e4feZm60Lyx+5o6Jk-ErQ8yCXTg@mail.gmail.com>
Subject: Re: Assigning reduce tasks to specific nodes
From: Jean-Marc Spaggiari <jean-marc@spaggiari.org>
To: user@hadoop.apache.org
Content-Type: text/plain; charset=UTF-8

Hi Hiroyuki,

Have you made any progress on that?

I'm also looking at a way to assign specific Map tasks to specific
nodes (I want the Map to run where the data is).

JM

2012/12/1, Michael Segel <michael_segel@hotmail.com>:
> I haven't thought about reducers but in terms of mappers you need to
> override the data locality so that it thinks that the node where you want to
> send the data exists.
> Again, not really recommended since it will kill performance unless the
> compute time is at least an order of magnitude greater than the time it
> takes to transfer the data.
>
> Really, really don't recommend it....
>
> We did it as a hack, just to see if we could do it and get better overall
> performance for a specific job.
>
>
> On Dec 1, 2012, at 6:27 AM, Harsh J <harsh@cloudera.com> wrote:
>
>> Yes, scheduling is done on a Tasktracker heartbeat basis, so it is
>> certainly possible to do absolutely strict scheduling (although be
>> aware of the condition of failing/unavailable tasktrackers).
>>
>> Mohit's suggestion is somewhat like what you desire (delay scheduling
>> in fair scheduler config) - but setting it to very high values is bad
>> to do (for jobs that don't need this).
>>
>> On Sat, Dec 1, 2012 at 4:11 PM, Hiroyuki Yamada <mogwaing@gmail.com>
>> wrote:
>>> Thank you all for the comments.
>>>
>>>> you ought to make sure your scheduler also does non-strict scheduling of
>>>> data local tasks for jobs
>>> that don't require such strictness
>>>
>>> I just want to make sure one thing.
>>> If I write my own scheduler, is it possible to do "strict" scheduling ?
>>>
>>> Thanks
>>>
>>> On Thu, Nov 29, 2012 at 1:56 PM, Mohit Anchlia <mohitanchlia@gmail.com>
>>> wrote:
>>>> Look at locality delay parameter
>>>>
>>>> Sent from my iPhone
>>>>
>>>> On Nov 28, 2012, at 8:44 PM, Harsh J <harsh@cloudera.com> wrote:
>>>>
>>>>> None of the current schedulers are "strict" in the sense of "do not
>>>>> schedule the task if such a tasktracker is not available". That has
>>>>> never been a requirement for Map/Reduce programs and nor should be.
>>>>>
>>>>> I feel if you want some code to run individually on all nodes for
>>>>> whatever reason, you may as well ssh into each one and start it
>>>>> manually with appropriate host-based parameters, etc.. and then
>>>>> aggregate their results.
>>>>>
>>>>> Note that even if you get down to writing a scheduler for this (which
>>>>> I don't think is a good idea, but anyway), you ought to make sure your
>>>>> scheduler also does non-strict scheduling of data local tasks for jobs
>>>>> that don't require such strictness - in order for them to complete
>>>>> quickly than wait around for scheduling in a fixed manner.
>>>>>
>>>>> On Thu, Nov 29, 2012 at 6:00 AM, Hiroyuki Yamada <mogwaing@gmail.com>
>>>>> wrote:
>>>>>> Thank you all for the comments and advices.
>>>>>>
>>>>>> I know it is not recommended to assigning mapper locations by myself.
>>>>>> But There needs to be one mapper running in each node in some cases,
>>>>>> so I need a strict way to do it.
>>>>>>
>>>>>> So, locations is taken care of by JobTracker(scheduler), but it is not
>>>>>> strict.
>>>>>> And, the only way to do it strictly is making a own scheduler, right
>>>>>> ?
>>>>>>
>>>>>> I have checked the source and I am not sure where to modify to do it.
>>>>>> What I understand is FairScheduler and others are for scheduling
>>>>>> multiple jobs. Is this right ?
>>>>>> What I want to do is scheduling tasks in one job.
>>>>>> This can be achieved by FairScheduler and others ?
>>>>>>
>>>>>> Regards,
>>>>>> Hiroyuki
>>>>>>
>>>>>> On Thu, Nov 29, 2012 at 12:46 AM, Michael Segel
>>>>>> <michael_segel@hotmail.com> wrote:
>>>>>>> Mappers? Uhm... yes you can do it.
>>>>>>> Yes it is non-trivial.
>>>>>>> Yes, it is not recommended.
>>>>>>>
>>>>>>> I think we talk a bit about this in an InfoQ article written by
>>>>>>> Boris
>>>>>>> Lublinsky.
>>>>>>>
>>>>>>> Its kind of wild when your entire cluster map goes red in ganglia...
>>>>>>> :-)
>>>>>>>
>>>>>>>
>>>>>>> On Nov 28, 2012, at 2:41 AM, Harsh J <harsh@cloudera.com> wrote:
>>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> Mapper scheduling is indeed influenced by the getLocations()
>>>>>>> returned
>>>>>>> results of the InputSplit.
>>>>>>>
>>>>>>> The map task itself does not care about deserializing the location
>>>>>>> information, as it is of no use to it. The location information is
>>>>>>> vital to
>>>>>>> the scheduler (or in 0.20.2, the JobTracker), where it is sent to
>>>>>>> directly
>>>>>>> when a job is submitted. The locations are used pretty well here.
>>>>>>>
>>>>>>> You should be able to control (or rather, influence) mapper placement
>>>>>>> by
>>>>>>> working with the InputSplits, but not strictly so, cause in the end
>>>>>>> its up
>>>>>>> to your MR scheduler to do data local or non data local assignments.
>>>>>>>
>>>>>>>
>>>>>>> On Wed, Nov 28, 2012 at 11:39 AM, Hiroyuki Yamada
>>>>>>> <mogwaing@gmail.com>
>>>>>>> wrote:
>>>>>>>>
>>>>>>>> Hi Harsh,
>>>>>>>>
>>>>>>>> Thank you for the information.
>>>>>>>> I understand the current circumstances.
>>>>>>>>
>>>>>>>> How about for mappers ?
>>>>>>>> As far as I tested, location information in InputSplit is ignored
>>>>>>>> in
>>>>>>>> 0.20.2,
>>>>>>>> so there seems no easy way for assigning mappers to specific nodes.
>>>>>>>> (I before checked the source and noticed that
>>>>>>>> location information is not restored when deserializing the
>>>>>>>> InputSplit
>>>>>>>> instance.)
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Hiroyuki
>>>>>>>>
>>>>>>>> On Wed, Nov 28, 2012 at 2:08 PM, Harsh J <harsh@cloudera.com>
>>>>>>>> wrote:
>>>>>>>>> This is not supported/available currently even in MR2, but take a
>>>>>>>>> look
>>>>>>>>> at
>>>>>>>>> https://issues.apache.org/jira/browse/MAPREDUCE-199.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Wed, Nov 28, 2012 at 9:34 AM, Hiroyuki Yamada
>>>>>>>>> <mogwaing@gmail.com>
>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>> Hi,
>>>>>>>>>>
>>>>>>>>>> I am wondering how I can assign reduce tasks to specific nodes.
>>>>>>>>>> What I want to do is, for example,  assigning reducer which
>>>>>>>>>> produces
>>>>>>>>>> part-00000 to node xxx000,
>>>>>>>>>> and part-00001 to node xxx001 and so on.
>>>>>>>>>>
>>>>>>>>>> I think it's abount task assignment scheduling but
>>>>>>>>>> I am not sure where to customize to achieve this.
>>>>>>>>>> Is this done by writing some extensions ?
>>>>>>>>>> or any easier way to do this ?
>>>>>>>>>>
>>>>>>>>>> Regards,
>>>>>>>>>> Hiroyuki
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> Harsh J
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> Harsh J
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Harsh J
>>
>>
>>
>> --
>> Harsh J
>>
>
>