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From "David Parks" <davidpark...@yahoo.com>
Subject RE: Large input files via HTTP
Date Tue, 23 Oct 2012 00:59:06 GMT
Would it make sense to write a map job that takes an unsplittable XML file
(which defines all of the files I need to download); that one map job then
kicks off the downloads in multiple threads. This way I can easily manage
the most efficient download pattern within the map job, and my output is
emitted as key,values straight to the reducer step?



From: vseetharam@gmail.com [mailto:vseetharam@gmail.com] On Behalf Of
Seetharam Venkatesh
Sent: Tuesday, October 23, 2012 7:28 AM
To: user@hadoop.apache.org
Subject: Re: Large input files via HTTP


One possible way is to first create a list of files with tuples<host:port,
filePath>. Then use a map-only job to pull each file using NLineInputFormat.


Another way is to write a HttpInputFormat and HttpRecordReader and stream
the data in a map-only job.

On Mon, Oct 22, 2012 at 1:54 AM, David Parks <davidparks21@yahoo.com> wrote:

I want to create a MapReduce job which reads many multi-gigabyte input files
from various HTTP sources & processes them nightly.

Is there a reasonably flexible way to acquire the files in the Hadoop job
its self? I expect the initial downloads to take many hours and I'd hope I
can optimize the # of connections (example: I'm limited to 5 connections to
one host, whereas another host has a 3-connection limit, so maximize as much
as possible).  Also the set of files to download will change a little over
time so the input list should be easily configurable (in a config file or

 - Is it normal to perform batch downloads like this *before* running the
mapreduce job?
 - Or is it ok to include such steps in with the job?
 - It seems handy to keep the whole process as one neat package in Hadoop if
 - What class should I implement if I wanted to manage this myself? Would I
just extend TextInputFormat for example, and do the HTTP processing there?
Or am I created a FileSystem?





“Perfection (in design) is achieved not when there is nothing more to add,
but rather when there is nothing more to take away.” 

- Antoine de Saint-Exupéry


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