Why does the oozie launcher consume 2 yarn containers?

问题

I am using Oozie to execute a spark job.

I "kind-of" understand that oozie lunches a map-only mapreduce job and from there lunches the spark-job.

What I do not understand is why this job consumes 2 yarn-containers?

In Yarn's resource manager page (titled "All Applications") I see something like this:

ID: application_nnnnn_3456 Name: oozie: launcher... Application Type: MAPREDUCE Running Containers: 2

ID: application_nnnnn_3457 Name: spark-app Application Type: SPARK Running Containers: 1

Is the oozie-launcher hosting 2 yarn application masters? One for the MAPREDUCE job and one for Spark job?

来源：https://stackoverflow.com/questions/41172110/why-does-the-oozie-launcher-consume-2-yarn-containers