I have tried

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 .


From: Bejoy Ks <bejoy.hadoop@gmail.com>
To: user@hadoop.apache.org; Shing Hing Man <matmsh@yahoo.com>
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 <bejoy.hadoop@gmail.com> wrote:

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 <matmsh@yahoo.com> 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 !