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MapReduce >> mail # user >> number of reducers

jamal sasha 2012-11-20, 19:38
Bejoy KS 2012-11-20, 20:09
Kartashov, Andy 2012-11-20, 21:50
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Re: number of reducers

 What is the relationship between number of reducers and cpu cores in your setup? I read somewhere that it must be .5 of number of cpu cores.




-----Original Message-----
From: Kartashov, Andy <[EMAIL PROTECTED]>
To: user <[EMAIL PROTECTED]>; bejoy.hadoop <[EMAIL PROTECTED]>
Sent: Tue, Nov 20, 2012 1:51 pm
Subject: RE: number of reducers

I specify mine inside mapred-site.xml

From: Bejoy KS [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, November 20, 2012 3:10 PM
Subject: Re: number of reducers

Hi Sasha

By default the number or reducers are set to be 1. If you want more you need to specify it as

hadoop jar myJar.jar myClass -D mapred.reduce.tasks=20 ...

Bejoy KS

Sent from handheld, please excuse typos.

From: jamal sasha <[EMAIL PROTECTED]>

Date: Tue, 20 Nov 2012 14:38:54 -0500



Subject: number of reducers



  I wrote a simple map reduce job in hadoop streaming.


I am wondering if I am doing something wrong ..

While number of mappers are projected to be around 1700.. reducers.. just 1?

It’s couple of TB’s worth of data.

What can I do to address this.

Basically mapper looks like this


For line in sys.stdin:

    Print line



For line in sys.stdin:

    New_line = process_line(line)

    Print new_line



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jamal sasha 2012-11-20, 20:24
Harsh J 2012-11-21, 04:08