Explanation
Correct code block:
from pyspark import StorageLevel
transactionsDf.persist(StorageLevel.MEMORY_ONLY_2).count()
Only persist takes different storage levels, so any option using cache() cannot be correct. persist() is evaluated lazily, so an action needs to follow this command. select() is not an action, but count() is - so all options using select() are incorrect.
Finally, the question states that "the executors' memory should be utilized as much as possible, but not writing anything to disk". This points to a MEMORY_ONLY storage level. In this storage level, partitions that do not fit into memory will be recomputed when they are needed, instead of being written to disk, as with the storage option MEMORY_AND_DISK. Since the data need to be duplicated across two executors, _2 needs to be appended to the storage level.
Static notebook | Dynamic notebook: See test 2