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