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From Harsh J <ha...@cloudera.com>
Subject Re: How can I limit reducers to one-per-node?
Date Sat, 09 Feb 2013 05:18:53 GMT
Hey David,

There's no readily available way to do this today (you may be
interested in MAPREDUCE-199 though) but if your Job scheduler's not
doing multiple-assignments on reduce tasks, then only one is assigned
per TT heartbeat, which gives you almost what you're looking for: 1
reduce task per node, round-robin'd (roughly).

On Sat, Feb 9, 2013 at 9:24 AM, David Parks <davidparks21@yahoo.com> 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.
> 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.

Harsh J

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