DDIA 是一本好書，但缺少練習回饋

DDIA is the best distributed systems book I have read. I finished the second edition with a head full of vocabulary and no way to check whether I actually understood any of it.

That is not a knock on the book. It has dozens of figures, real company stories, and code for a small key-value store. What it does not have is a feedback loop. No exercises. No answer key. No failure timeline you can step through. No numbers you can change and watch break.

The gap shows up in interviews. You can explain linearizability and still freeze when the old leader comes back with a stale lease. You can describe two-phase commit, or 2PC, and still not know what a participant does after it votes yes and the coordinator disappears.

So I built the lab I wanted while reading it.

The uncomfortable part

Reading DDIA cover to cover is not a flex. Most people finish it with a warm feeling and no changed decisions. I did that the first time.

The book is a map. Maps are useful. But you do not learn a city by reading a map, and you do not learn a distributed system by nodding at a diagram. You learn it when you have to choose between two designs, defend the choice, and find the failure that kills it.

Most study notes make this worse. They compress a chapter into definitions and arrows, then delete the part where you have to think. You finish the summary and feel productive. You still cannot answer the interview question.

The exercises here are not "summarize chapter 6." They are "the leader dies here, the client retries there, show me the duplicate and the fix."

If you have read DDIA and never changed a design because of it, you read a good book. You did not practice.

What is in it

14 chapters, in English and Persian, with the full content in both.

155 chapter diagrams. 89 are interactive step-throughs: write paths, failovers, quorums, 2PC, compaction. 66 are hand-built concept diagrams: UML, timelines, decision trees. Every diagram is followed by a teacher-style walkthrough that reads the figure step by step. Not a caption.

302 worked examples. Each one has the same shape: initial state, operation, result and reason. The numbers are teaching numbers, labeled as such.

47 design exercises with full worked solutions, plus 118 diagrams inside those solutions. The exercises are leveled for foundation, senior and staff roles, and tagged by priority.

A capstone that turns the chapters into one AI platform design: requirements, estimates, 15 ADRs, recovery targets and a developer journey.

The state that made 2PC click

Two-phase commit looks simple on a whiteboard. Prepare, commit, done. The hard part is the gap between a yes vote and a decision.

Initial state: participant A voted yes. It is prepared, holds locks, and waits for the coordinator.

Operation: the coordinator disappears. A times out.

Result: A cannot commit or abort on its own. It keeps the locks until it learns the decision, or until an operator decides by hand. A timeout is not information. Releasing the locks early breaks atomicity.

That is the kind of state I could not practice by reading. I could nod at it. I could not reason through it under pressure.

The diagram is not decoration. It is the exercise. You trace the arrows, find the two points of no return, and see why "just retry" is not a recovery strategy.

What it is not

It is not a replacement for DDIA. The book is the source. The lab is the practice.

It is not a production system. The capstone is a design workshop. Everything proposed is labeled proposed. There are no fake benchmarks or invented SLOs.

It is not a coding course. The 47 exercises are design and interview drills, not "implement a B-tree in 300 lines." Some have optional lab extensions, but the main path is reasoning on a whiteboard.

Why two languages

I read in English and explain in Persian. Most DDIA notes pick one language. Every chapter page has a toggle, and the same content exists in both. If you are learning technical English, the side-by-side version is useful on its own.

Try it

Start with chapter 4 if you want storage engines, or chapter 10 if you want consensus. The exercise audit page lists the level and evidence for every drill.

Repo: https://github.com/Hurdadd/ddia-study-lab

Site: https://ddia-study-lab.vercel.app/

If this helps you prepare, star the repo. If a diagram is wrong, open an issue. I would rather fix the diagram than keep the star.