https://tech.daniellbastos.com.br/tags/cost-formulas/Recent content in Cost Formulas on Daniel's Tech BlogHugoen-usFri, 17 Apr 2026 00:00:00 +0000https://tech.daniellbastos.com.br/posts/chapter-4-cost-formulas/Fri, 17 Apr 2026 00:00:00 +0000https://tech.daniellbastos.com.br/posts/chapter-4-cost-formulas/<blockquote> <p>This post continues the study of <a href="https://courses.cs.duke.edu/compsci516/cps216/spring03/papers/selinger-etal-1979.pdf">Access Path Selection in a Relational Database Management System (Selinger et al., 1979)</a>, now covering chapter 4. I used available internet resources and tools to go deeper on the examples and make the concepts more concrete.</p> </blockquote> <h2 id="what-chapter-4-covers">What chapter 4 covers</h2> <p>Chapter 4 describes how the optimizer estimates the cost of each access path available for a single relation and picks the cheapest one. It introduces the catalog statistics the optimizer depends on, the selectivity factors applied to different predicate types, and the cost formulas for each possible situation: unique index with equality, clustered and non-clustered indexes with and without matching predicates, and the segment scan fallback.</p>