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From Karl Anderson <...@monkey.org>
Subject Re: Hadoop complex calculations
Date Mon, 01 Dec 2008 22:29:32 GMT

On 25-Nov-08, at 7:38 AM, Chris Quach wrote:

> Hi,
> I'm testing Hadoop to see if we could use for complex calculations  
> next to
> the 'standard' implementation. I've set up a grid with 10 nodes and  
> if I run
> the RandomTextWriter example only 2 nodes are used as mappers, while I
> specified 10 mappers to be used. The other nodes are used for  
> storage, but I
> want them to also execute the map function. (I've had this same  
> behaviour
> with my own test program..)
> Is there a way to tell the framework to use all available nodes as  
> mappers?
> Thanks in advance,
> Chris

Assuming you have more than two tasks to run in total, you're probably  
seeing all nodes being used, but only 2 at once.  If you're only  
seeing two *tasks*, that's your problem, set mapred.map.tasks and  

If that isn't it, make sure mapred.tasktracker.map.tasks.maximum and  
mapred.tasktracker.reduce.tasks.maximum are large enough in hadoop- 
site.xml on each node. AFAIK setting conf parameters within the job or  
by command-line flags has no effect on these.  If you use the hadoop- 
ec2 tools, you can do this with hadoop-ec2-env.sh.

Karl Anderson

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