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MapReduce >> mail # user >> RE: Map output compression in Hadoop 1.0.3


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RE: Map output compression in Hadoop 1.0.3

Hi Andy and list,

Apologies - I've not been looking at my list inbox for a while, so missed this request. I'm running some tests as I type, and will report back when they're done. I'm running the same job for bzip2, gzip and snappy codecs versus no map out compression. I guess I should include LZO in the comparison too, but the codec wasn't obvious in the o.a.h.io.compress.* areas of Hadoop. If someone could point out where to find this codec, that'd be really handy. If not I could always google it :)

Tony

________________________________________
From: Kartashov, Andy [[EMAIL PROTECTED]]
Sent: 29 November 2012 16:09
To: [EMAIL PROTECTED]
Subject: RE: Map output compression in Hadoop 1.0.3

Tony,

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?

Rgds,
AK

-----Original Message-----
From: Tony Burton [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, November 28, 2012 6:38 AM
To: <[EMAIL PROTECTED]>
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 API.

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:[EMAIL PROTECTED]]
Sent: 28 November 2012 11:25
To: <[EMAIL PROTECTED]>
Subject: Re: Map output compression in Hadoop 1.0.3

Hi,

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 <[EMAIL PROTECTED]> 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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Harsh J
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