根据spark2.2的编译顺序来确定源码阅读顺序，只阅读核心的基本部分。
1、common目录
①Tags
②Sketch
③Networking
④Shuffle Streaming Service
⑤Unsafe
2、launcher目录
3、core目录
spark的编译顺序是：
[INFO] Reactor Build Order:
[INFO]
[INFO] Spark Project Parent POM
[INFO] Spark Project Tags
[INFO] Spark Project Sketch
[INFO] Spark Project Networking
[INFO] Spark Project Shuffle Streaming Service
[INFO] Spark Project Unsafe
[INFO] Spark Project Launcher
[INFO] Spark Project Core
[INFO] Spark Project ML Local Library
[INFO] Spark Project GraphX
[INFO] Spark Project Streaming
[INFO] Spark Project Catalyst
[INFO] Spark Project SQL
[INFO] Spark Project ML Library
[INFO] Spark Project Tools
[INFO] Spark Project Hive
[INFO] Spark Project REPL
[INFO] Spark Project Assembly
[INFO] Spark Project External Flume Sink
[INFO] Spark Project External Flume
[INFO] Spark Project External Flume Assembly
[INFO] Spark Integration for Kafka 0.8
[INFO] Kafka 0.10 Source for Structured Streaming
[INFO] Spark Project Examples
[INFO] Spark Project External Kafka Assembly
[INFO] Spark Integration for Kafka 0.10
[INFO] Spark Integration for Kafka 0.10 Assembly