Designing Data-Intensive Applications, 2nd Edition

Designing Data-Intensive Applications

*The big ideas behind reliable, scalable, and maintainable systems. Martin Kleppmann & Chris Riccomini (2nd edition, 2026)*

The handful of brutally hard problems hiding under everything

Open your phone. The feed that loaded in under a second was assembled from posts written by hundreds of people you follow, somehow ranked and merged and delivered before your thumb finished its swipe. The message you sent landed on a friend's screen on another continent. A search box guessed what you meant before you finished typing. None of this feels remarkable, because it almost always works.

Now imagine it doesn't. A small news site gets linked from somewhere huge, and the instant the traffic hits, the whole thing melts: pages time out, the database falls over, and the more users retry, the deeper it sinks, until it never recovers even after the crowd leaves. Or picture a bank transfer that debits one account but the matching deposit silently never lands, and now money has simply evaporated inside a computer. Or two servers that both, at the same moment, become convinced they are in charge of the same data, and quietly start corrupting it in ways nobody notices for hours. Every one of these is a real failure mode, and every app you touched today is quietly solving the same small set of genuinely hard problems to avoid them.

That is what this book is about. Not one database, not one framework, but the durable principles underneath all of them: how to store data so you can get it back fast, how to keep copies in sync across machines that fail and clocks that lie, how to stay correct when the network drops packets at the worst possible moment, and ultimately, what we owe the people whose lives are encoded in all that data. We will move through three movements: the lens the whole book hands you (every decision is a trade-off, measured against reliability, scalability, and maintainability); the heart of it, distributed data, where replication, consistency, and consensus turn out to be much harder and more interesting than they look; and the close, where the authors put down the engineering and ask the uncomfortable question, technical excellence in service of what?