From the Preface Who is this book for? In conversations at technical conferences, I often hear the same question: “How can I learn more about database internals? I don’t even know where to start.” Most of the books on database systems do not go into details of storage engine implementation, and cover the access methods, such as B-Trees, on a rather high level. There are very few books that cover more recent concepts, such as different B-Tree variants and log-structured storage, so I usually recommend reading papers. Everyone who reads papers knows that it’s not that easy: you often lack context, the wording might be ambiguous, there’s little or no connection between papers, and they’re hard to find. This book contains concise summaries of important database systems concepts and can serve as a guide for those who’d like to dig in deeper, or as a cheat sheet for those already familiar with these concepts. Not everyone wants to become a database developer, but this book will help people who build software that uses database systems: software developers, reliability engineers, architects, and engineering managers. If your company depends on any infrastructure component, be it a database, a messaging queue, a container platform, or a task scheduler, you have to read the project change-logs and mailing lists to stay in touch with the community and be up-to-date with the most recent happenings in the project. Understanding terminology and knowing what’s inside will enable you to yield more information from these sources and use your tools more productively to troubleshoot, identify, and avoid potential risks and bottlenecks. Having an overview and a general understanding of how database systems work will help in case something goes wrong. Using this knowledge, you’ll be able to form a hypothesis, validate it, find the root cause, and present it to other project maintainers. This book is also for curious minds: for the people who like learning things without immediate necessity, those who spend their free time hacking on something fun, creating compilers, writing homegrown operating systems, text editors, computer games, learning programming languages, and absorbing new information. The reader is assumed to have some experience with developing backend systems and working with database systems as a user. Having some prior knowledge of different data structures will help to digest material faster.