Quality matrix¶
This is a quality audit, not a page-count. A green status in project status is only honest if the page teaches the way a senior engineer actually works.
How we audited¶
We cannot close-read 150 files in one pass. The method:
- Deep-read the first-release vertical slice (README + the first table in project status): methodology, CAP/sharding/hashing/Raft, Kafka/stampede/breaker/tail latency, the four flagship designs, the three DSA pattern pages, the two behavioural stories, the debugging playbook, K8s, and the first-release cloud/reliability pages.
- Sample every other Complete pillar (one or two pages): LLD (OOP + Parking Lot), security (OAuth vs privacy), architecture (EDA vs batch/ETL), messaging extras (Pulsar), networking extras (gRPC/K8s), growth-mindset, remaining design exercises (Ad Serving).
- Grep the rest for Predict / V1 / bottleneck / trade-off / exit / failure / Mermaid or sim embed / estimates. Hits are not automatic ✓ — a word in passing is ~.
- Conservative symbols. If a heading exists but the section does not actually do the job (a "Key Takeaways" that restates definitions, a diagram with no prediction), mark ~ not ✓.
- Applicable columns only. Behavioural pages n/a simulation and BOE. DSA n/a production ops and design-V1 (brute force counts as V1 when it is actually written). Catalogs (failure library, cheat sheets) n/a evolution. Process pages (ADRs) n/a capacity math.
Demotion rule (CROSS-6): if a module marked Complete has 3+ applicable ✗, it is Needs review — finished prose is not Complete.
Symbols: ✓ present and doing the job · ~ partial / implied · ✗ missing · — not applicable.
| Column | What “present” means |
|---|---|
| Req | Opens on a problem / requirements, not a definition |
| Pred | Predict-before-reveal, reasoning exercise, or “predict the log line” |
| # | Back-of-envelope or concrete numbers that change the design |
| V1 | Simplest viable system (or brute force, for DSA) |
| Fail | Named bottleneck or failure that V1 cannot survive |
| Mech | Mechanism introduced because of that failure, not because it is fashionable |
| Viz | Mermaid and/or a working sim where it would actually help |
| Prod | Production caveat, debugging, or “this lie will page you” |
| TO | Explicit trade-off defense (table or A vs B with a decision) |
| Exit | Exit criteria, self-assessment, or “you can do X when…” |
First-release vertical slice (deep)¶
| Module | Req | Pred | # | V1 | Fail | Mech | Viz | Prod | TO | Exit |
|---|---|---|---|---|---|---|---|---|---|---|
| Design methodology | ✓ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Requirements & estimation | ✓ | ~ | ✓ | ✓ | ✓ | ~ | ✓ | ✓ | ~ | ✓ |
| CAP theorem | ✓ | ~ | ✓ | — | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Sharding | ✓ | ✗ | ~ | ~ | ✓ | ~ | ✓ | ✓ | ✓ | ~ |
| Consistent hashing | ✓ | ✗ | ✓ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ~ |
| Raft | ✓ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Kafka consumer groups | ✓ | ✗ | ✓ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Cache stampede | ✓ | ~ | ✓ | ~ | ✓ | ✓ | ✓ | ~ | ✓ | ~ |
| Circuit breaker | ✓ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ~ |
| Tail latency | ✓ | ✓ | ✓ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ~ |
| URL shortener | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Rate limiter (exercise) | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ~ | ✓ | |
| Payments | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Sliding window | ✓ | ✗ | ~ | ✓ | — | ✓ | ✓ | — | ~ | ~ |
| BFS / DFS | ✓ | ✗ | — | ✓ | — | ✓ | ✓ | — | ~ | ~ |
| Dynamic programming | ✓ | ✗ | ~ | ✓ | — | ✓ | ✓ | — | ~ | ✓ |
| Technical disagreement | ✓ | — | — | — | ✓ | — | — | ✓ | ~ | ✓ |
| Production incident | ✓ | — | — | — | ✓ | — | — | ✓ | — | ✓ |
| Debugging playbook | ✓ | ~ | ✓ | — | ✓ | ✓ | — | ✓ | ~ | ✓ |
| Kubernetes | ✓ | ~ | ~ | — | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Docker | ✓ | ✗ | ~ | — | ✓ | ✓ | ✓ | ✓ | ✓ | ~ |
| Terraform | ✓ | ~ | ✗ | ✗ | ✓ | ~ | ✓ | ✓ | ✓ | ~ |
| CI/CD | ✓ | ✗ | ✗ | ✗ | ~ | ~ | ✓ | ✓ | ~ | ~ |
| Deployment strategies | ✓ | ✗ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ~ |
| IAM & managed services | ✓ | ✗ | ~ | ✗ | ✓ | ✓ | ~ | ✓ | ✓ | ~ |
| FinOps | ✓ | ~ | ✓ | — | ✓ | ~ | ~ | ✓ | ✓ | ~ |
| Model serving | ✓ | ~ | ✓ | ✓ | ✓ | ✓ | ~ | ✓ | ✓ | ~ |
| Microservices communication | ✓ | ✗ | ✗ | ✗ | ✓ | ~ | ✓ | ✓ | ✓ | ~ |
| Stateless vs stateful | ✓ | ✗ | ~ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Single points of failure | ✓ | ✗ | ✗ | ✗ | ✓ | ~ | ✓ | ✓ | ~ | ~ |
| Consistency models | ✓ | ✓ | ~ | — | ✓ | ~ | ✓ | ✓ | ✓ | ✓ |
| Replication | ✓ | ~ | ✓ | — | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Indexing | ✓ | ✓ | ✓ | — | ✓ | ✓ | ~ | ✓ | ✓ | ✓ |
| SQL vs NoSQL | ✓ | ✓ | ✓ | — | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Engineering mathematics | ✓ | ~ | ✓ | — | ✓ | ✓ | ✓ | ~ | ~ | ✓ |
| Queue patterns | ✓ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Cache strategies | ✓ | ✓ | ✓ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Failure library | ✓ | — | ✓ | — | ✓ | ✓ | — | ✓ | ~ | ~ |
| Distributed cache (ex) | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Load balancer (ex) | ✓ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| API gateway (ex) | ✓ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ~ |
| Notification system (ex) | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Web crawler (ex) | ✓ | ~ | ✓ | ✓ | ✓ | ~ | ✓ | ✓ | ✓ | ~ |
| Autocomplete (ex) | ✓ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ~ |
| Distributed KV (ex) | ✓ | ~ | ✓ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ~ |
| Social feed (ex) | ✓ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
First-release notes
- Gold standard is the four flagship exercises plus CAP / Raft / circuit breaker / cache strategies / queue patterns. Those already are the method.
- Sharding, consistent hashing, Kafka have working sims and production sections but no predict-before-click task on the host page (the sim is used as a demo). That is ~ / ✗ Pred, not a demotion by itself.
- Terraform, CI/CD, SPOF, microservices communication miss 3+ applicable columns → demoted. They read as finished notes, not a reasoning loop.
- SQL Deep Dive is labeled Complete in the old tracker and Draft on the databases hub. Draft wins.
Sampled Complete pillars¶
| Module | Req | Pred | # | V1 | Fail | Mech | Viz | Prod | TO | Exit | Verdict |
|---|---|---|---|---|---|---|---|---|---|---|---|
| OOP fundamentals | ✓ | ✗ | ✗ | ✗ | ~ | ~ | ~ | ~ | ✓ | ~ | Needs review |
| SOLID | ✓ | ✗ | ✗ | ✗ | ~ | ~ | ~ | ~ | ✓ | ~ | Needs review |
| Design patterns | ✓ | ✗ | ✗ | ✗ | ~ | ~ | ~ | ~ | ✓ | ~ | Needs review |
| Concurrency basics | ✓ | ~ | ✗ | ✗ | ✓ | ~ | ✓ | ✓ | ✓ | ~ | Needs review |
| Concurrency execution models | ✓ | ~ | ~ | — | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | Complete |
| Parking Lot (LLD) | ✓ | ✓ | — | ✓ | ✓ | ✓ | ✓ | — | ✓ | ~ | Complete (sample of the 15) |
| OAuth2 & OIDC | ✓ | ~ | ~ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | Complete |
| Session management | ✓ | ~ | ~ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | Complete |
| Threat modeling | ✓ | — | ~ | — | ✓ | ✓ | ✓ | ~ | ~ | ~ | Complete (process page) |
| AuthN/Z | ✓ | ✗ | ✗ | ~ | ✗ | ✓ | ✓ | ✓ | ~ | ~ | Needs review |
| Zero Trust | ✓ | ✗ | ✗ | ~ | ✓ | ✓ | ✓ | ✓ | ✗ | ~ | Needs review |
| Data privacy | ✓ | ✗ | ✗ | ✗ | ~ | ~ | ✓ | ~ | ✗ | ~ | Needs review |
| Web vulns | ✓ | ~ | ~ | ✗ | ✓ | ✓ | ✓ | ✗ | ✗ | ~ | Needs review |
| Kafka internals / Pulsar | ✓ | ✗ | ✗ | ✗ | ✓ | ~ | ✗ | ✓ | ✗ | ~ | Needs review |
| Pulsar primer | ✓ | ✗ | ✗ | ✗ | ~ | ✓ | ✗ | ✓ | ✗ | ~ | Needs review |
| Event-driven architecture | ✓ | ~ | ~ | ~ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | Complete |
| Batch/ETL Lambda vs Kappa | ✓ | ✗ | ✗ | ✗ | ✓ | ✓ | ✓ | ✓ | ✗ | ~ | Needs review |
| gRPC vs HTTP in K8s | ✓ | ✗ | ✓ | — | ✓ | ✗ | ✓ | ✓ | ✗ | ~ | Needs review |
| Modern protocols / mesh | ✓ | ✗ | ✗ | — | ✗ | ✗ | ✓ | ✓ | ~ | ~ | Needs review |
| Realtime communication | ✓ | ✗ | ✗ | ✗ | ✓ | ✓ | ✓ | ✓ | ✓ | ~ | Needs review |
| API design | ✓ | ~ | ✗ | ✗ | ✓ | ✓ | ✓ | ✓ | ✗ | ~ | Needs review |
| ADRs | ✓ | — | — | — | ✓ | ✓ | — | ✓ | ✓ | ~ | Complete (process) |
| Architecture reviews | ✓ | — | ~ | — | ✓ | ✓ | — | ✓ | ✓ | ~ | Complete (process) |
| DDIA concepts | ✓ | ~ | ~ | — | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | Complete |
| SQL Deep Dive | ✓ | ✗ | ✗ | ✗ | ~ | ~ | ✗ | ✗ | ~ | ~ | Needs review (already Draft on the hub) |
| Ad Serving (ex) | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | Complete (V1-first sample of the 21) |
| Self-respect | ✓ | — | — | — | ✓ | — | — | ✓ | ✓ | ~ | Complete (judgement, not STAR) |
| Release engineering | ✓ | ✗ | ✗ | ~ | ✓ | ✓ | ✓ | ✓ | ✗ | ~ | Needs review |
Grep pass (remaining Complete labels)¶
Not a close read. Sections found → ✓ or ~. Three-plus applicable ✗ still demoted.
| Cluster | Typical shape | Notes |
|---|---|---|
| Remaining design exercises (Pastebin → Video calling, capstone) | ✓ Req # V1 Fail Mech Prod TO Exit; Pred ~; Viz ~ | Written to the Pastebin “evolves and clicks” bar. Keep Complete. A pedagogy pass on leftover dumps is still listed under Planned. |
| Remaining LLD exercises (15) | ✓ Req V1 Fail Viz; Pred ~; # —; Prod —; Exit ~ | 9-step + class diagrams + concurrency. Sampled Parking Lot. Keep Complete. |
| DSA Interactive pages (heaps → Aho-Corasick) | ✓ pattern + viz; Pred ✗ on most | Status is Interactive, not Complete — out of this matrix. |
| DSA written Complete (foundations, two pointers, binary search, pattern recognition) | ✓ problem/pattern; Pred ~; Fail/Mech/TO weak | Keep Complete as DSA-bar pages (same as sliding-window), not system-design-bar. Pred-before-viz is the remaining gap. |
| Distributed fundamentals, multi-region DR, CRDTs, stream processing, serverless vs containers, multi-tenancy, microservices vs monolith | ✓ Req Fail Prod; Pred/V1 often ~ | Keep Complete. Not gold-slice. |
| Observability: production reliability, testing strategy | ✓ Req Fail Prod; TO ~ | Keep Complete. |
| Behavioural remaining 7 + growth-mindset remaining 6 | ✓ story/judgement; engineering columns — | Keep Complete. |
| Reference: cheat sheets, glossary, trade-off matrix | catalogs | Keep Complete as reference, not concept. Exit is weak (no “you can do X”). |
| Performance fundamentals | ✓ numbers/fail; Viz ✗; Mech ~ | Keep Complete. |
Demoted this pass (Complete → Needs review)¶
| Page | Why (applicable ✗) |
|---|---|
| SQL Deep Dive | Tracker said Complete; hub already said Draft. No prediction, V1, visual, production-debug, or failure-driven mechanism. |
| Terraform | No capacity numbers, no smallest-justified V1, no bottleneck chain. State/drift are taught, but not as a reasoning loop. |
| CI/CD | Pipeline catalog. Missing prediction, numbers, V1, bottleneck, mechanism-from-failure. |
| Release engineering | Missing prediction, numbers, trade-off defense. |
| Single points of failure | Missing prediction, numbers, V1. SPOF hunt is the skill; the page does not make you practice it. |
| Microservices communication | Eight patterns listed. No numbers, no V1 (sync REST), no prediction. |
| Batch/ETL Lambda vs Kappa | Missing prediction, numbers, V1, trade-off table. |
| Kafka internals & Pulsar | Internals dump. Missing prediction, numbers, V1, visual, trade-off defense. |
| Pulsar primer | Ops dump. Missing prediction, numbers, V1, bottleneck, visual, trade-off. |
| Modern protocols & mesh | Missing prediction, numbers, bottleneck, mechanism-from-failure. |
| gRPC vs HTTP in K8s | Long production notes; missing prediction, mechanism-from-named-failure, trade-off defense. |
| Realtime communication | Missing prediction, numbers, V1. |
| API design | Missing numbers, V1, trade-off defense. |
| OOP / SOLID / patterns / concurrency basics | Definition pages. Missing prediction, numbers, V1. Execution-models stays Complete. |
| AuthN/Z | Missing prediction, numbers, bottleneck identification. |
| Zero Trust | Missing prediction, numbers, trade-off defense. |
| Data privacy | Missing prediction, numbers, V1, bottleneck, mechanism, production, trade-off. |
| Web vulnerability classes | Missing V1, production debugging, trade-off defense. |
Vendor DB pages (postgresql, mongodb, cassandra, dynamodb, redis) were already Draft — left alone.
Remaining gaps (do not pretend these are done)¶
- Predict-before-click on host sim pages (Kafka, sharding, hash ring, stampede, Raft). The failure-injection lab is the stopgap, not a substitute for a box on each host page.
- Exit criteria as a named heading. Most pages have Key Takeaways; few say “you are done when you can…”.
- DSA visualizers still run as demos. Brute-force-first and “predict the next highlight” are rare.
- Demoted pages need a quality pass, not more topics.
- Interview-mode tabs, capstone UX, and Go example parity remain Planned.
- No new system-design #41. Freeze expansion until Completes on this matrix are honest.