Spring Boot, GraphQL, TestContainers, PostgreSQL: Minimal Setup

This tip provides a minimalistic quickstart code for setting up a module using Spring Boot, GraphQL, PostgreSQL, and TestContainers.
Spark SQL: Partitions and Sizes

Data fetching parallelisation in Apache Spark through Spark SQL / JDBC.
PartitionColumn, lowerBound, upperBound, numPartitions and a lot of other parameters: how do they work?