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

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One mapper/reducer runs on a single JVM
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,