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MapReduce, mail # user - Re: How to find the num of Mappers


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Sai Sai 2013-04-12, 08:21
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Re: How to find the num of Mappers
Nitin Pawar 2013-04-12, 09:05
your question is answered here
http://wiki.apache.org/hadoop/HowManyMapsAndReduces

To answer first part of your question,

it is not mandatory to run all the maps of a given job at a single time.
Maps are executed as and when the map slots are available on the
tasktrackers
On Fri, Apr 12, 2013 at 1:51 PM, Sai Sai <[EMAIL PROTECTED]> wrote:

> If we have a 640 MB data file and have 3 Data Nodes in a cluster.
> The file can be split into 10 Blocks and starts the Mappers M1, M2,  M3
> first.
> As each one completes the task M4 and so on will be run.
> It appears like it is not necessary to run all the 10 Map tasks in
> parallel at once.
> Just wondering if this is right assumption.
> What if we have 10 TB of data file with 3 Data Nodes, how to find the
> number of mappers that will be created.
> Thanks
> Sai
>

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Nitin Pawar