Modernizing from PostgreSQL to Serverless with Fauna Part 3` provides an in-depth look at referential integrity, trade-offs in data modeling strategies, query optimization concepts, indexes, and document and relational data types in Fauna. The text discusses how Fauna can implement methods of referential integrity, including unique constraints, foreign keys, and cascading deletes, as well as how to ensure data integrity without native support for these actions. It also explores alternative modeling strategies, such as denormalization, where related data is often embedded directly within a document or record rather than stored in separate tables. Additionally, the text covers user-defined functions (UDFs) as equivalents to stored procedures, hybrid schema enforcement, zero-downtime migrations, check constraints, and indexes. Fauna's schemaless document model offers flexibility in data structure and adapts easily to changing requirements, making it suitable for applications that require high scalability and low latency. The text concludes by highlighting the benefits of using Fauna as a superset of document and relational databases when migrating from Postgres to serverless architecture.