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From Susheel Kumar Gadalay <skgada...@gmail.com>
Subject Re: Re: Question about shuffle/merge/sort phrase
Date Mon, 22 Dec 2014 05:40:38 GMT
What I explained is shuffle phase.

After the reducer pulls the data, it does a sort on the key part only
and calls the corresponding reduce method.
On 12/22/14, bit1129@163.com <bit1129@163.com> wrote:
> Then what exactly happens after Reducer pulls all mapper output key/value
> pairs from all the mapper nodes before reducer see the
> <key,value1,value2..>?
>
>
>
> bit1129@163.com
>
> From: Susheel Kumar Gadalay
> Date: 2014-12-22 13:20
> To: user
> Subject: Re: Question about shuffle/merge/sort phrase
> Sorry, typo
>
> It is the reducer which will pull the mapper o/p as soon as it completes.
>
> On 12/22/14, Susheel Kumar Gadalay <skgadalay@gmail.com> wrote:
>> It is the mapper which will push the o/p to the respective reducer as
>> soon as it completes.
>>
>> The no of reducers are known at the beginning itself.
>> The mapper as it process the input split, generate the o/p of for each
>> reducer (if the mapper o/p key is eligible for the reducer).
>> The reducer will wait till the completion of all map tasks to start it
>> processing.
>>
>>
>> On 12/22/14, bit1129@163.com <bit1129@163.com> wrote:
>>> Could some one help me on this question? thanks.
>>>
>>>
>>>
>>> bit1129@163.com
>>>
>>> 发件人: Todd
>>> 发送时间: 2014-12-21 21:59
>>> 收件人: user@hadoop.apache.org
>>> 主题: Question about shuffle/merge/sort phrase
>>> Hi, Hadoopers,
>>> I got a question about shuffle/sort/merge phrase related..
>>> My understanding is that shuffle is used to transfer the mapper
>>> output(key/value pairs) from mapper node to reducer node, and merge
>>> phrase
>>> is used to merge all the mapper output from all mapper nodes, and sort
>>> phrase is used to sort the key/value pair by key,
>>> Then my question, whose responsibility is it that brings each key with
>>> all
>>> its values together (The reducer's input is a key and an iterative
>>> values).
>>>
>>>
>>> Thanks.
>>>
>>
>

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