This article explores the evolution, design, and inner workings of the ext4 extent mechanism in Linux, detailing how it replaces traditional block mapping, improves storage efficiency, reduces fragmentation, and accelerates file I/O through compact data structures and B+‑tree indexing.
This article explains the purpose, design, and internal data structures of ext4 extents, describes how the B+‑tree indexes extents for efficient mapping of logical to physical blocks, and compares ext4’s extent mechanism with older file‑system addressing methods and other modern file systems.
This article explains where MySQL keeps its data files, how InnoDB organizes tablespaces into segments, extents, pages and rows, details the Compact row format—including variable‑length field length lists, NULL‑value lists, and hidden fields—and clarifies the limits of VARCHAR and row‑overflow handling.
