PostgreSQL Performance Tuning, Part IV: Designing and Implementing Your Database Schema` is about optimizing database schema design to achieve optimal query performance, minimize I/O operations, ensure efficient CPU and memory utilization, and reduce storage requirements. The article discusses how to design schemas around your query pattern, minimize storage cost by arranging columns in the table definition from largest to smallest data type, and consider partitioning for large tables to boost ingest and query performance. It also covers best practices for designing schemas that can accommodate append-only ingestion, backfilling, and ingestion with updates. The article emphasizes the importance of understanding your query pattern, leveraging highly selective indexes, caching computed data, and avoiding vacuuming and running out of background workers.