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From Vinod Kumar Vavilapalli <vino...@hortonworks.com>
Subject Re: What are the methods to share dynamic data among mappers/reducers?
Date Thu, 02 Jan 2014 18:21:03 GMT

There isn't anything natively supported for that in the framework, but you can do that yourselves
by using a shared service (for e.g via HDFS files, ZooKeeper nodes) that mappers/reducers
all have access to.

More details on your usecase? In any case, once you start making mappers and reducers depend
on either externally changing state or inter-dependence, you may be breaking fundamental assumptions
of MapReduce - embarrassingly parallel computation (limiting scalability) and/or idempotency
(affecting retries during failures).

Thanks,
+Vinod

On Jan 2, 2014, at 1:42 AM, sam liu <samliuhadoop@gmail.com> wrote:

> Hi,
> 
> As I know, the Distributed Cache will copy the shared data to the slaves before starting
job, and won't change the shared data after that. 
> 
> So are there any solutions to share dynamic data among mappers/reducers?
> 
> Thanks!


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