[Yarn] Executor cores isolation

[Peter Rudenko]

Hi i have a question: how does the cores isolation works on spark on 
yarn. E.g. i have a machine with 8 cores, but launched a worker with 
--executor-cores 1, and after doing something like:

rdd.foreachPartition(=>{for all visible cores: burn core in a new tread})
Will it see 1 core or all 8 cores?

Thanks,
Peter Rudenko