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MapReduce >> mail # user >> One mapper/reducer runs on a single JVM

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Re: One mapper/reducer runs on a single JVM
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 it.
On Nov 5, 2012, at 7:12 PM, Lin Ma <[EMAIL PROTECTED]> 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