01
Design an Agentic Task Execution Platform
The crux
When an irreversible tool call's outcome is unknown, what may you retry, and what must you verify first?
New · Volume 2 · Correctness Under Uncertainty
Five advanced interviews where the obvious answer breaks.
A practice-first workbook for SDE-2 / SDE-3 engineers who have to reason about retries, stale authorization, deletion, decision stability, and contention — the places where a plausible design quietly loses correctness.
251-page professionally designed PDF · 50 diagrams · 32-point D1–D8 rubric · Instant download
5
advanced interview simulations
16
structured sections per problem
50
architecture & state diagrams
251
page professional PDF
Free sample · no risk
Run the first interview before you buy.
Download the free sample and attempt Problem 1 — Agentic Task Execution: the prompt, clarification, capacity math, and the design, stopping right at the §9 Stop Gate before the reference solution. Real workbook pages, not a brochure.
What's inside the free sample
- The practice method and the 16-section arc
- Problem 1 opening: prompt, clarification, requirements, capacity estimation
- Agentic execution practice up to the Stop Gate
- The §9 Stop Gate — commit your design before the solution
- The five problems and the D1–D8 rubric, in overview
The through-line
One rule runs through all five problems.
Volume 2 is about correctness when the system isn't sure what happened. An action fires; its outcome is unknown; you must verify authoritatively before you retry — or risk doing it twice, honoring stale authority, or resurrecting deleted data. Every problem is a different disguise of the same discipline.
Action→ Unknown→ Verified→ Safe Retry
The one rule — verify before you retry.
Inside Volume 2
Five advanced problems, five failure modes.
Each runs the full 16-section arc — prompt, clarification, capacity math, architecture, deep dives, interviewer challenges, a Stop Gate, trade-off tables, reference diagrams, and self-grading. Each turns on a single hard question.
02
Design Permission-Aware Enterprise Retrieval
The crux
Who is authorized under the request's declared contract — not merely "now"?
03
Design Distributed Deletion Across Derived Systems
The crux
How does a deletion become a durable, dominant fact that replays, rebuilds, and restores cannot resurrect?
04
Design a Real-Time Payment Risk Platform
The crux
A committed decision must be replayed on retry, not re-scored across a model rollout.
05
Design a High-Contention Ticketing Platform
The crux
When payment and hold-expiry race for one scarce seat, where is the single deciding transition?
See what you're actually getting
Real spreads from Volume 2.
Actual pages from the 251-page workbook, not mockups. Click any page to read it full size.
How each problem is built
A 16-section arc that forces the work.
The same disciplined sequence carries every problem — the structure is the product. Three mechanics do the heavy lifting.
01 / STOP GATE · §9
Commit before you read
At §9 the workbook stops you: write your requirements, your capacity math, and your design. Only then do you compare against the reference solution. No passive scrolling past the hard part.
02 / INTERVIEWER CHALLENGES
Defend under pressure
Each problem includes the pushback a real interviewer applies — the plausible-but-wrong follow-ups that test whether your design actually holds once the outcome is uncertain.
03 / D1–D8 SELF-GRADING
Know where it breaks
Score every attempt across eight dimensions, 0–4, mapped to the evidence you produced. Read your total — and the gate dimensions — before a real interviewer does.
SELF-GRADE · D1–D80–4 PER DIMENSION
D1 · Requirements & scoping
D2 · Estimation & constraints
D3 · API & data model
D5 · Durable plan & side-effects
D6 · Crash recovery & reconciliation
+ D4, D7, D8
Gate → D5 ≥ 3
Gate → D6 ≥ 3
+ flagship challenge
Honest scoring
A rubric built for correctness, not vibes.
- 8 dimensions, scored 0–4 — 32 points. Each dimension is mapped to specific evidence you produce during the simulation, so a score is defensible, not a guess.
- Gate dimensions. D5 (durable plan & side-effects) and D6 (crash recovery & reconciliation) must each clear 3/4, plus the problem's flagship challenge — because that's where correctness under uncertainty is actually won or lost.
- Regrade on every rep. Problems are built to be re-attempted, so the same score sheet shows movement across passes instead of a one-time verdict.
Honest fit
This is the advanced volume.
Built for you if
- You're comfortable with core distributed systems and have done Volume 1 or equivalent reps
- You're targeting senior / staff SDE-3 loops where correctness reasoning is graded
- You want to practise retries, stale authority, deletion, decision stability, and contention
- You want to find where your design loses correctness — through self-grading, not reassurance
Skip it if
- You're new to backend or system design — start with fundamentals, then Volume 1
- You only want short answers to memorize
- You're looking for a beginner theory textbook or a reference encyclopedia
- You're interviewing for roles without a system design round
Get Volume 2
One payment. Start practicing today.
Buy Volume 2 on its own, or get both volumes for $39 — $9 less than buying them separately.
Volume 2 only
Correctness Under Uncertainty
$29
one-time purchase
- 251-page professionally designed PDF
- 5 advanced interview simulations
- 50 architecture & state diagrams
- Stop gates, interviewer challenges, reference solutions
- 32-point D1–D8 self-grading rubric
- Practice Pack + Read-Me bonuses
- Lifetime updates to Volume 2
Secure checkout via Gumroad · 7-day refund window · eligibility applies
Prices in USD. Currency conversion and applicable taxes are shown at checkout.
Best value
Volume 1 + Volume 2
The complete library
$39
both workbooks · one-time purchase
- Everything in Volume 2
- Volume 1 — five foundational interview simulations (127 pages)
- Ten complete problems across both volumes
- Core practice through advanced correctness exercises
- Lifetime updates to both volumes
Secure checkout via Gumroad · 7-day refund window · eligibility applies
Prices in USD. Currency conversion and applicable taxes are shown at checkout.
Already own Volume 1? Use code V1OWNER at checkout for Volume 2 at $19.
| Volume 1 | Volume 2 | |
|---|---|---|
| Focus | Foundational patterns & the practice method | Correctness under uncertainty |
| Problems | LLM serving, feed, rate limiter, scheduler, collaborative editor | Agentic execution, permission-aware retrieval, distributed deletion, payment risk, ticketing |
| Arc | 12-section simulation | 16-section simulation + Stop Gate at §9 |
| Rubric | 32-point, 8 dimensions | 32-point D1–D8, with gate dimensions |
| Length | 127-page PDF | 251-page PDF · 50 diagrams |
| Level | SDE-2 → SDE-3 | SDE-3 / staff correctness reasoning |
FAQ
Questions, answered.
Do I need Volume 1 first?
No — Volume 2 is standalone. It assumes you're comfortable with core distributed-systems building blocks, but it doesn't depend on Volume 1's problems. If you want the full path from foundational to advanced, the bundle gives you both.
How is Volume 2 different from Volume 1?
Volume 1 builds the practice method across foundational problems. Volume 2 is the advanced volume: five problems centred on correctness under uncertainty — retries, stale authorization, deletion, decision stability, and contention — with a longer 16-section arc, a Stop Gate at §9, and the D1–D8 rubric with gate dimensions.
What format do I get?
A 251-page professionally designed PDF with 50 diagrams, built for reading, printing and annotating. It works offline once downloaded, on any device that opens a PDF. Purchase includes the Practice Pack and a Read-Me guide.
What level is it pitched at?
Senior engineers preparing for SDE-3 / staff-level loops, and strong SDE-2s who want to practise correctness reasoning. You should already know what a load balancer, cache, queue and consensus protocol are — the workbook trains you to defend designs when outcomes are uncertain.
What is the Stop Gate?
At §9 of every problem the workbook stops and asks you to commit your design — requirements, capacity math, and architecture — before it shows the reference solution. It's the mechanic that turns reading into interview reps.
How are the files delivered?
Checkout is handled by Gumroad. After payment you get an immediate download link for the PDF and bonuses, plus an emailed receipt with permanent access to the same files.
Do I get updates?
Yes. Every revision of Volume 2 is free for buyers.
Can I get a refund?
Refund requests may be submitted within 7 days; eligibility conditions apply. Because this is a digital product, refunds are intended for accidental duplicate purchases, technical issues preventing access to the files, or if the workbook materially differs from its description. Email contact@practicesystemdesign.com with your order details. See the Refund Policy for full details.
The whole idea
The obvious answer is the trap. Practice the one that holds.
Clarify the problem. Estimate the load. Draw the architecture. Then commit at the Stop Gate, compare against the reference, and grade yourself on the dimensions that decide correctness — five times over.