Reading about RDD Persistency <https://spark.apache.org/docs/latest/programming-guide.html#rdd-persistence>, I learned that the storage level "MEMORY_AND_DISK" means that " Store RDD as deserialized Java objects in the JVM. If the RDD does not fit in memory, store the partitions that don't fit on disk, and read them from there when they're needed. "
But how can a "deserialized Java object" be stored on disk? As far as I know, a Java object should be stored as an array of bytes on disk, which means that Java object should be firtly converted into an array of bytes (a serialized object). Thanks .
