Home | About | Sematext search-lucene.com search-hadoop.com
 Search Hadoop and all its subprojects:

Switch to Threaded View
MapReduce >> mail # dev >> Understanding the MapOutput

Copy link to this message
Re: Understanding the MapOutput
Hi Pedro,

The format is called IFile. Check out the source for more info on the
format - it's fairly simple. The partition starts are recorded in a
separate index file next to the output file.

I don't think you'll find significant docs on this format since it's
MR-internal - the code is your best resource.


On Fri, Nov 4, 2011 at 8:37 AM, Pedro Costa <[EMAIL PROTECTED]> wrote:
> Hi,
> I'm trying to understand the structure of the map output file. Here's an
> example of a mapoutput file that contains 2 partitions:
> [code]
> <FF><FF><FF><FF>^@^@716banana banana apple banana carrot carrot apple
> banana 0apple carrot carrot carrot banana carrot carrot 5^N4carrot apple
> carrot apple apple carrot banana apple ^Mbanana apple <FF><FF><DF>|<8E><B7>
> [/code]
> 1 - I would like to understand what are the ASCII characters parts. What
> they means?
> 2 - What type of file is a map output? Is it a SequenceFileOutputFormat, or
> a TextOutputFormat?
> 3 - I've a small program that runs independently of the MR that has the
> goal to digest each partition and give the correspondent hash. How do I
> know where each partition starts?
> --
> Thanks,

Todd Lipcon
Software Engineer, Cloudera