Why PostgreSQL Skips Your Index: A Lesson in Cost-Based Optimization

Most developers assume indexes guarantee performance improvements, but PostgreSQL's cost-based optimizer often bypasses them when sequential scans are more efficient. This article reveals the fundamental principle: optimization is about minimizing total work, not following indexing conventions. Understanding how PostgreSQL actually makes these decisions is essential for developers building scalable systems, transforming slow query troubleshooting from trial-and-error into systematic optimization.