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From Nan Zhu <zhunans...@gmail.com>
Subject Re: How can I limit reducers to one-per-node?
Date Sat, 09 Feb 2013 04:59:38 GMT
those nodes with 2 reducers were running these two r at the same time? if yes, I think you
can change mapred-site.xml as I suggested,  

if no, i.e. your goal is to make all nodes take the same number of tasks in the life cycle
of job….I don't know if there is any provided property can do this….

Best,  

--  
Nan Zhu
School of Computer Science,
McGill University



On Friday, 8 February, 2013 at 11:46 PM, David Parks wrote:

> Looking at the Job File for my job I see that this property is set to 1, however I have
3 reducers per node (I’m not clear what configuration is causing this behavior).
>   
> My problem is that, on a 15 node cluster, I set 15 reduce tasks on my job, in hopes that
each would be assigned to a different node, but in the last run 3 nodes had nothing to do,
and 3 other nodes had 2 reduce tasks assigned.
>   
>   
>   
> From: Nan Zhu [mailto:zhunansjtu@gmail.com]  
> Sent: Saturday, February 09, 2013 11:31 AM
> To: user@hadoop.apache.org (mailto:user@hadoop.apache.org)
> Subject: Re: How can I limit reducers to one-per-node?
>   
> I haven't use AWS MR before…..if your instances are configured with 3 reducer slots,
it means that 3 reducers can run at the same time in this node,   
>  
>   
>  
> what do you mean by "this property is already set to 1 on my cluster"?
>  
>   
>  
> actually this value can be node-specific, if AWS MR instance allows you to do that, you
can modify mapred-site.xml to change it from 3 to 1
>  
>   
>  
> Best,
>  
>   
>  
> --  
>  
> Nan Zhu
>  
> School of Computer Science,
>  
> McGill University
>  
>   
>  
>  
> On Friday, 8 February, 2013 at 11:24 PM, David Parks wrote:
> >  
> > Hmm, odd, I’m using AWS Mapreduce, and this property is already set to 1 on my
cluster by default (using 15 m1.xlarge boxes which come with 3 reducer slots configured by
default).
> >  
> >  
> >   
> >  
> >  
> >   
> >  
> >  
> >   
> >  
> >  
> > From: Nan Zhu [mailto:zhunansjtu@gmail.com]  
> > Sent: Saturday, February 09, 2013 10:59 AM
> > To: user@hadoop.apache.org (mailto:user@hadoop.apache.org)
> > Subject: Re: How can I limit reducers to one-per-node?
> >  
> >  
> >   
> >  
> >  
> > I think set tasktracker.reduce.tasks.maximum  to be 1 may meet your requirement
> >  
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> > Best,
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> > --  
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> >  
> >  
> > Nan Zhu
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> >  
> > School of Computer Science,
> >  
> >  
> >  
> > McGill University
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> > On Friday, 8 February, 2013 at 10:54 PM, David Parks wrote:
> > >  
> > > I have a cluster of boxes with 3 reducers per node. I want to limit a particular
job to only run 1 reducer per node.
> > >  
> > >  
> > >   
> > >  
> > >  
> > > This job is network IO bound, gathering images from a set of webservers.
> > >  
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> > >   
> > >  
> > >  
> > > My job has certain parameters set to meet “web politeness” standards (e.g.
limit connects and connection frequency).
> > >  
> > >  
> > >   
> > >  
> > >  
> > > If this job runs from multiple reducers on the same node, those per-host limits
will be violated.  Also, this is a shared environment and I don’t want long running network
bound jobs uselessly taking up all reduce slots.
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