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From Harsh J <ha...@cloudera.com>
Subject Re: Input splits for sequence file input
Date Mon, 03 Dec 2012 04:27:57 GMT
Hi Jeff,

This has been asked several times before (check out
http://search-hadoop.com please).

The answer is (3) for SequenceFiles (due to no notion of records) and
(2) as a general thought (i.e. text files, etc.).

On Mon, Dec 3, 2012 at 3:33 AM, Jeff LI <uniquejeff@gmail.com> wrote:
> Hello,
>
> I was reading on the relationship between input splits and HDFS blocks and a
> question came up to me:
>
> If a logical record crosses HDFS block boundary, let's say block#1 and
> block#2, does the mapper assigned with this input split asks for (1) both
> blocks, or (2) block#1 and just the part of block#2 that this logical record
> extends to, or (3) block#1 and part of block#2 up to some sync point that
> covers this particular logical record?  Note the input is sequence file.
>
> I guess my question really is: does Hadoop operate on a block basis or does
> it respect some sort of logical structure within a block when it's trying to
> feed the mappers with input data.
>
> Cheers
>
> Jeff
>



-- 
Harsh J

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