Databases

Five lessons covering how databases work under the hood.

Storage engines (how data is organized on disk — pages, heaps, and the choice between row and column stores), indexes (how B-trees and hash indexes make queries fast), transactions (ACID properties and how databases guarantee correctness), write-ahead logging (how databases survive crashes without losing data), and query execution (how SQL becomes a plan that reads indexes and scans tables).

Every application depends on a database. Understanding what happens beneath the SQL explains why some queries are fast and others are slow, why indexes matter, and why transactions have the guarantees they do. The glossary defines every term. The FAQ answers common questions.