Aidan Wang

Engineering Manager · writing about complex systems and tech leadership

Complex systems explained with one diagram and concise text.

The blog is written in Traditional Chinese and translated post by post: 137 of 189 posts are in English so far, across 13 of 18 series. Everything else falls back to the Chinese original under the same URL, so links never dead-end.

Start here → About me 中文首頁

Featured series

Designing Data-Intensive Applications — Reading Notes

12 posts in English

DDIA chapter by chapter: data models, storage engines, replication, partitioning, transactions, all the way to the trade-offs of distributed systems.

Re:Building a Live-Commerce Platform from Zero

21 posts in English

War stories: rebuilding a real live-commerce platform — ordering by comment, inventory, payments and fulfillment; how it was done then, how I'd design it now.

Fundamentals of Data Engineering — Reading Notes

11 posts in English

The whole map of data engineering — a mental model built along the data engineering lifecycle, not held hostage by any one tool.

The full map — all 18 series, with the untranslated posts marked → see everything

Latest in English

Private complaints:"Ralph smells bad" Placating Tell the complainers to put up with it→ someone quits Blaming "You stink — deal with it"→ Ralph hurt, still doesn't know why Super-reasonable All-hands email: "mind your hygiene"→ everyone feels accused — except Ralph Irrelevant Do nothing, wait for it to pass→ it gets worse Congruent Talk to Ralph — privately, directly→ Ralph sees a doctor, and says thanks Dots = self (top) / other (left) / context (right); filled = attended to, hollow = ignored

Leadership — Power and Congruence

· tech · 21 min read · 📚 Becoming a Tech Leader — Reading Notes #11

The last two chapters of the motivation part (Ch14–15) are about power — but the power Weinberg mean…

#leadership

Each comparison can only split the remaining permutations in two a < b ? b < c ? a < c ? < > a b c a < c ? b a c b < c ? < > < > a c b c a b b c a c b a < > < > n! leaves → height ≥ log₂(n!) ≈ n log n → at least n log n comparisons in the worst case

Sorting Is the Cheapest Structure: The Comparison Lower Bound, Counting Sort, and Binary Search

· tech · 22 min read · 📚 Competitive Programmer's Handbook — Reading Notes #2

Part one was about reading $n$ and knowing which complexity to write. This part covers CPHB chapter …

#algorithms#cphb#sorting#binary-search#book-notes

1-second limit ≈ a few hundred million ops: read n, infer the complexity input size n acceptable complexity typical approach operations n ≤ 10 O(n!) try every permutation 10! ≈ 3.6×10⁶ n ≤ 20 O(2ⁿ) try every subset 2²⁰ ≈ 10⁶ n ≤ 500 O(n³) three nested loops 500³ ≈ 1.3×10⁸ n ≤ 5000 O(n²) two loops, every pair 5000² = 2.5×10⁷ n ≤ 10⁶ O(n log n) or O(n) sort, or one pass 10⁶×20 = 2×10⁷ n is large O(log n) or O(1) binary search, a formula — e.g. n = 10⁵ with O(n²) → 10¹⁰ ops, tens of seconds — known before writing a line

Read n, and You Know What to Write: Time Complexity and the Maximum Subarray Sum

· tech · 25 min read · 📚 Competitive Programmer's Handbook — Reading Notes #1

A new series: reading Antti Laaksonen's Competitive Programmer's Handbook (CPHB). It's the companion…

#algorithms#cphb#complexity#book-notes

231 CI runs Green 194 Cancelled 22 Red 15 The 15 red runs, by cause Tests 8 Lint 4 Infrastructure 3 mypy 0 What the 8 test failures caught Silent bug ×3 state reads CLEAN One OS ×2 confirmed One OS ×2 log expired flaky All 15 on PR branches Reached master: 0 "Log expired": we know which OS went red, not which test. The flaky one is the only PR merged on red. 22 cancelled: 21 master runs superseded by a newer merge, 1 PR run superseded by a new push.

Guardrail Engineering: The New Role of Tests and Specs on an AI Production Line

· tech · 26 min read · 📚 The Craft of Working with AI (2026) #7

The first post defined guardrails as "tools for widening the neck" — hand the checks a person would …

#ai#testing#side-project

Author, blind Bare AI +CLAUDE.md +review skill B1 reversed index logic boundary △ "no test pins it" not verified 3/3 3/3 3/3 B2 Apply → Pop silent regression ✓ 3/3 3/3 3/3 B3 layer bypass architecture call ✓ 1/3 2/3 3/3 Unplanted real bug half-done, says "error" ✗ 1/3 1/3 3/3 Cost 20 minutes 0.4–2.2 min, $0.09–0.19 per run How B1 was checked Read the diff 8 of 9 tested pygit2 with a script

The Craft of Acceptance: How to Review AI's Code

· tech · 29 min read · 📚 The Craft of Working with AI (2026) #6

The first post said the width of the neck is the bandwidth you have for accepting work responsibly; …

#ai#code-review#leadership

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