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From Michael Segel <michael_se...@hotmail.com>
Subject Re: One mapper/reducer runs on a single JVM
Date Tue, 06 Nov 2012 04:46:54 GMT
Mappers and Reducers are separate JVM processes.
And yes you need to take in to account the amount of memory the machine(s) when you configure
the number of slots. 

If you are running just Hadoop, you could have a little swap. Running HBase, fuggit about

On Nov 5, 2012, at 7:12 PM, Lin Ma <linlma@gmail.com> wrote:

> Hello Hadoop experts,
> I have a question in my mind for a long time. Supposing I am developing M-R program,
and it is Java based (Java UDF, implements mapper or reducer interface). My question is, in
this scenario, whether a mapper or a reducer is a separate JVM process? E.g. supposing on
a machine, there are 4 mappers, they are 4 individual processes? I am also wondering whether
the processes on a single machine will impact each other when each JVM wants to get more memory
to run faster?
> thanks in advance,
> Lin

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