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Subject: Re: One mapper/reducer runs on a single JVM
From: Michael Segel <michael_segel@hotmail.com>
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 <CAK_MoSs96iMKYND4jnKS90KwaMjHiYKMbu5zV3CX-A5NjWT_mQ@mail.gmail.com>
Date: Mon, 5 Nov 2012 22:46:54 -0600
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 <CAK_MoSs96iMKYND4jnKS90KwaMjHiYKMbu5zV3CX-A5NjWT_mQ@mail.gmail.com>
To: user@hadoop.apache.org

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.=20

If you are running just Hadoop, you could have a little swap. Running =
HBase, fuggit about it.=20


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

> Hello Hadoop experts,
>=20
> 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?
>=20
> thanks in advance,
> Lin
>=20
>=20