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From "Kartashov, Andy" <Andy.Kartas...@mpac.ca>
Subject RE: Map output compression in Hadoop 1.0.3
Date Thu, 29 Nov 2012 16:09:10 GMT

Can you please share with us on the permorfmance improvement (if any) after using compression
in map.output? I was abpout to start looking into it myself.   What compression codec did
you use?


-----Original Message-----
From: Tony Burton [mailto:TBurton@SportingIndex.com]
Sent: Wednesday, November 28, 2012 6:38 AM
To: <user@hadoop.apache.org>
Subject: RE: Map output compression in Hadoop 1.0.3

Also, another point that prompted my initial question: I'd come across "mapred.compress.map.output"
in the documentation, but I wasn't 100% sure if there has been or will be any equivalence
or correspondence between config setting like this one and the naming of the stable and new

For example, we've got o.a.h.mapreduce.Job rather than o.a.h.mapred.JobConf as previously
mentioned, from the "mapred" and "mapreduce" parts of the API.

Are config settings that begin with mapred.* related to the stable API with the implication
that there's an mapreduce.* equivalent (eg mapred.compress.map.output vs mapreduce.compress.map.output),
or am I seeing a connection that doesn't exist?

(Hope that makes sense!)

-----Original Message-----
From: Harsh J [mailto:harsh@cloudera.com]
Sent: 28 November 2012 11:25
To: <user@hadoop.apache.org>
Subject: Re: Map output compression in Hadoop 1.0.3


The property mapred.output.compress, as its name reads, controls job-output compression, not
intermediate/transient data compression, which is what you mean by "Map output compression".

Also note that this property is a per job one and can be toggled, if a user wanted, on/off
for each job specifically.

These should be the many ways, exhaustively, for MR1, to turn on "Map output compression":

1. Set "mapred.compress.map.output" to true in your client's mapred-site.xml to turn it on
for all jobs run from such a client machine.
2. Set the above in cluster, with <final>true</final> at every node (JT plus TTs)
and restart them, to turn it on for all job, regardless of what the job itself specifies.
3. Turn it on per-job basis:
3.1. Stable API: JobConf.setCompressMapOutput(true);
3.2. New API: Job.getConfiguration().set("mapred.compress.map.output", true);

On Wed, Nov 28, 2012 at 4:42 PM, Tony Burton <TBurton@sportingindex.com> wrote:
> Hi,
> Quick question: What's the best way to turn on Map Output Compression
> in Hadoop 1.0.3? The tutorial at
> http://hadoop.apache.org/docs/r1.0.3/mapred_tutorial.html says to use
> JobConf.setCompressMapOutput(boolean), but I'm using
> o.a.h.mapreduce.Job rather than o.a.h.mapred.JobConf.
> Is it simply a case of using getConf.set("mapred.output.compress",
> true) then constructing my Job from the Configuration object, or is
> there more direct way that I've missed?
> Thanks,
> Tony
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