This is Part 2 of a 15-part Apache Iceberg Masterclass . Part 1 covered why table formats exist. This article breaks down exactly how each format organizes its metadata. The metadata structure of a table format determines everything: how fast queries start planning, how efficiently concurrent writes are handled, how schema changes propagate, and how much overhead accumulates over time. Two formats can both claim "ACID support" and "time travel" while having fundamentally different mechanisms under the hood. Table of Contents What Are Table Formats and Why Were They Needed? The Metadata Structure of Current Table Formats Performance and Apache Iceberg's Metadata Technical Deep Dive on Partition Evolution Technical Deep Dive on Hidden Partitioning Writing to an Apache Iceberg Table What Are Lakehouse Catalogs?…