I was referring to the doc - https://kb.databricks.com/clusters/spark-executor-memory.

In general total off heap memory is  =  spark.executor.memoryOverhead + spark.offHeap.size.  The off-heap mode is controlled by the properties spark.memory.offHeap.enabled. 

Could you please clarify :

• difference between  spark.executor.memoryOverhead  vs spark.offHeap.size ? when to use one over other?
• In what use-cases/scenarios/operations Spark needs offheap memory
• when we set spark.memory.offHeap.enabled to false, does it disables only 'spark.offHeap.size' or both spark.executor.memoryOverhead  and spark.offHeap.size?