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MapReduce >> mail # user >> Re: Input Split vs Task vs attempt vs computation


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Re: Input Split vs Task vs attempt vs computation
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Best Regards,
Sonal
Nube Technologies <http://www.nubetech.co>

<http://in.linkedin.com/in/sonalgoyal>
On Fri, Sep 27, 2013 at 10:42 AM, Sai Sai <[EMAIL PROTECTED]> wrote:

> Hi
> I have a few questions i am trying to understand:
>
> 1. Is each input split same as a record, (a rec can be a single line or
> multiple lines).
>

An InputSplit is a chunk of input that is handled by a map task. It will
generally contain multiple records. The RecordReader provides the key
values to the map task. Check
http://hadoop.apache.org/docs/stable/api/org/apache/hadoop/mapreduce/InputSplit.html

>
> 2. Is each Task a collection of few computations or attempts.
>
> For ex: if i have a small file with 5 lines.
> By default there will be 1 line on which each map computation is performed.
> So totally 5 computations r done on 1 node.
>
> This means JT will spawn 1 JVM for 1 Tasktracker on a node
> and another JVM for map task which will instantiate 5 map objects 1 for
> each line.
>
> i am not sure what you mean by 5 map objects. But yes, the mapper will be
invoked 5 times, once for each line.
> The MT JVM is called the task which will have 5 attempts for  each line.
> This means attempt is same as computation.
>
> Please let me know if anything is incorrect.
> Thanks
> Sai
>
>