In this chapter, we examined a powerful tool in Apex library—the SQL API (Calcite integration)—and how it enables us to build classical ETL applications using SQL to automatically create many operators and link them into the DAG. We also covered how to build the application to produce the application archive (.apa) file which can be deployed in a cluster.
We also saw how to run the integration test locally, on our development machine, to enable detection of bugs, configuration errors, and other defects early in the development process, without the need to install Hadoop, ZooKeeper, or Kafka. We then took a detailed look at the application log messages and saw how to interpret them.
We rounded out the chapter by summarizing the classes involved in the Calcite integration.