Scala language:
Apache Spark architecture:
The Spark programming guide is the primary resource for concepts; refer to the language-specific API documents for a complete list of operations available:
Resilient Distributed Datasets: A Fault-Tolerant Abstraction for In-Memory Cluster Computing by Matei Zaharia and others is the original source for RDD basics:
Spark Summit, the official event series of Apache Spark, has a wealth of the latest information. Check out past events' presentations and videos: