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MapReduce, mail # user - Re: Assigning reduce tasks to specific nodes


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Re: Assigning reduce tasks to specific nodes
Jean-Marc Spaggiari 2012-12-07, 19:51
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 <[EMAIL PROTECTED]>:
> 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 <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]>
>> 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 <[EMAIL PROTECTED]>
>>> wrote:
>>>> Look at locality delay parameter
>>>>
>>>> Sent from my iPhone
>>>>
>>>> On Nov 28, 2012, at 8:44 PM, Harsh J <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]>
>>>>> 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
>>>>>> <[EMAIL PROTECTED]> 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...
>>>>>>> :-)
>>>>>>