About
daemon in Spark
The daemon in Spark are the driver that starts the executors. See Spark - Cluster
The daemon in Spark are JVM running threads (known as core (or slot)
- one driver = 1 JVM many core
- one executor = 1 JVM many core
As the JVM has to startup and initialize certain data structures before it can begin running tasks, running more core is preferable as running more executors.