Introduction: The Unseen Costs of Indexes When we talk about database performance, indexes are usually the first thing that comes to mind. When a query runs slowly, the first place we look is often for missing or incorrect indexes. We generally know what B-tree, GIN, and BRIN index types do and when to use them. We even have those famous graphs from PostgreSQL documentation in our minds. But in the real world, especially in large and complex systems, how much do we question why these basic index choices often fall short, or even sometimes degrade performance? In this post, I'll explain with concrete examples from my own experiences why index selections cannot be made by just looking at table and query structures, and how organizational workflows, data distribution, and even hardware can influence these decisions.…