Progress Tracker

Auto-updated after each quiz. Latest at the top.

Summary

Phase status

• Phase 1 (Foundations, Days 1-7): ✅ COMPLETE
• Phase 2 (Data & Storage, Days 8-14): In progress — Days 8, 9, 10 ✅ done, Day 11 next

Chronic gaps

All resolved. No gap has failed on 2+ consecutive tests since Day 8.

Weak areas (revisit queue) — none are chronic, only pending re-quiz

Strengths (confirmed)

• L4/L7 LB fundamentals + all 5 modern LB algorithms
• HTTP status codes, idempotency, statelessness → horizontal scaling
• HTTP caching headers precise semantics
• DNS TTL implications; Anycast BGP vs DNS-based routing
• Little's Law application
• Jeff Dean numbers — all 5 anchors memorized
• Back-of-envelope math including in scenario answers
• Postgres-specific debugging (PgBouncer, pg_stat_statements, VACUUM, autovacuum)
• TCP vs UDP fundamentals + HOL blocking
• Push mechanism selection including bidirectional check
• All 6 cache layers + all 4 write strategies
• Cache-key pollution recognition
• Cascading /healthz trap awareness; sticky sessions decision
• Retry amplification root cause analysis
• Hit-rate math + request vs byte hit rate distinction
• Cache stampede naming + mitigation
• Hot-key problem + mitigations
• CDC scaling pattern
• L1 cache trade-off recognition
• Multi-region cache architecture
• Refresh pattern mapping
• Senior-level post-mortem structure — consistent Days 3/5/6/7/8/9 Q9
• Origin shield / request coalescing / single-flight vocabulary
• JWT vs sessions trade-off precision
• Global CDN architecture design
• DB selection by access pattern (not by scale alone)
• LSM vs B-tree storage engine reasoning
• Chat storage architecture with full capacity math + hot partition mitigation + tiered storage
• Polyglot persistence + migration path
• ANSI isolation level anomaly mapping (Day 9 Q6 — 5/5)
• Write skew recognition and Serializable-only property (Day 9 Q1)
• Read Committed vs Repeatable Read precise semantics (Day 9 Q2)
• Flash-sale atomic conditional UPDATE pattern (Day 9 Q3)
• ACID-C vs CAP-C precision (Day 9 Q4)
• SSI vs 2PL deep vocabulary — "dangerous structures", MVCC, dependency tracking (Day 9 Q7)
• Per-workload isolation-level selection (Day 9 Q8 — Staff-level nuance)
• Ticket-booking architecture with seat-per-row model + soft-hold state machine (Day 9 Q8)
• Defense-in-depth thinking — DB unique constraint as backstop for app logic (Day 9 Q9)
• Lock-contention math with correct units (decrements/sec, not QPS) (Day 9 Q8)
• Composite index leading-column + equality-before-range rule (Day 10 Q1, Q6, Q8)
• Partial index for hot-minority queries (Day 10 Q3, Q8)
• Postgres visibility map + index-only scan mechanics (Day 10 Q7 — Staff-level)
• Partial-predicate immutability trap (NOW() - breaks partial indexes) (Day 10 Q8 — rare knowledge)
• HOT-update awareness on Postgres storage engine (Day 10 Q8 — Postgres-DBA-level)
• "Sargable" — precise SQL vocabulary (Day 10 Q9)
• Index-cost / write-amp analysis with math (Day 10 Q8)
• 3-clause root-cause post-mortem TL;DR structure (Day 10 Q9)

Daily log