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From alx...@aim.com
Subject Re: number of reducers
Date Tue, 20 Nov 2012 22:00:57 GMT

 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.

Thanks.
Alex.

 

 

-----Original Message-----
From: Kartashov, Andy <Andy.Kartashov@mpac.ca>
To: user <user@hadoop.apache.org>; bejoy.hadoop <bejoy.hadoop@gmail.com>
Sent: Tue, Nov 20, 2012 1:51 pm
Subject: RE: number of reducers



I specify mine inside mapred-site.xml
 
<property>
    <name>mapred.reduce.tasks</name>
    <value>20</value>
  </property>
 
Rgds,
AK47

From: Bejoy KS [mailto:bejoy.hadoop@gmail.com]
Sent: Tuesday, November 20, 2012 3:10 PM
To: user@hadoop.apache.org
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 ...

Regards
Bejoy KS

Sent from handheld, please excuse typos.



From: jamal sasha <jamalshasha@gmail.com> 

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

To: <user@hadoop.apache.org>

ReplyTo: user@hadoop.apache.org 

Subject: number of reducers

 



Hi,

  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

 

Reducer

For line in sys.stdin:

    New_line = process_line(line)

    Print new_line

 

 

Thanks


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