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Re: How to lower the total number of map tasks
I only have one big input file.

Shing
________________________________
 From: Bejoy KS <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]; Shing Hing Man <[EMAIL PROTECTED]>
Sent: Tuesday, October 2, 2012 6:46 PM
Subject: Re: How to lower the total number of map tasks
 

Hi Shing

Is your input a single file or set of small files? If latter you need to use CombineFileInputFormat.
Regards
Bejoy KS

Sent from handheld, please excuse typos.
________________________________

From:  Shing Hing Man <[EMAIL PROTECTED]>
Date: Tue, 2 Oct 2012 10:38:59 -0700 (PDT)
To: [EMAIL PROTECTED]<[EMAIL PROTECTED]>
ReplyTo:  [EMAIL PROTECTED]
Subject: Re: How to lower the total number of map tasks
I have tried
       Configuration.setInt("mapred.max.split.size",134217728);

and setting mapred.max.split.size in mapred-site.xml. ( dfs.block.size is left unchanged at 67108864).

But in the job.xml, I am still getting mapred.map.tasks =242 .

Shing
________________________________
 From: Bejoy Ks <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]; Shing Hing Man <[EMAIL PROTECTED]>
Sent: Tuesday, October 2, 2012 6:03 PM
Subject: Re: How to lower the total number of map tasks
 

Sorry for the typo, the property name is mapred.max.split.size

Also just for changing the number of map tasks you don't need to modify the hdfs block size.
On Tue, Oct 2, 2012 at 10:31 PM, Bejoy Ks <[EMAIL PROTECTED]> wrote:

Hi
>
>
>You need to alter the value of mapred.max.split size to a value larger than your block size to have less number of map tasks than the default.
>
>
>
>On Tue, Oct 2, 2012 at 10:04 PM, Shing Hing Man <[EMAIL PROTECTED]> wrote:
>
>
>>
>>
>>I am running Hadoop 1.0.3 in Pseudo  distributed mode.
>>When I  submit a map/reduce job to process a file of  size about 16 GB, in job.xml, I have the following
>>
>>
>>mapred.map.tasks =242
>>mapred.min.split.size =0
>>dfs.block.size = 67108864
>>
>>
>>I would like to reduce   mapred.map.tasks to see if it improves performance.
>>I have tried doubling  the size of  dfs.block.size. But the    mapred.map.tasks remains unchanged.
>>Is there a way to reduce  mapred.map.tasks  ?
>>
>>
>>Thanks in advance for any assistance !  
>>Shing
>>
>>
>