The twelve threads traced across the series:
| Thread | Book 1 Root | Book 3 Form | Book 4 Form | Book 6 Form |
|---|---|---|---|---|
| T1 Hashing | Modular arithmetic | Consistent hashing, sharding | Partition strategy | ID design |
| T2 Trees | BST, B-tree | Database index | Search index, trie | — |
| T3 Graphs | BFS, DFS, Dijkstra | Service dependency | Social graph, routing | Conway’s Law |
| T4 Queues | FIFO | Message queue, Kafka | Fan-out, notifications | Async handoff |
| T5 Caching | Memoization, DP | Redis, CDN | Precomputed feeds | — |
| T6 Redundancy | Set membership | DB replication | Multi-region | Reliability SLO |
| T7 State Machines | Finite automata | Event sourcing, CQRS | Order lifecycle | Incident lifecycle |
| T8 Divide & Conquer | Merge sort | MapReduce, sharding | Microservices | Team decomposition |
| T9 Consensus | Proof | Raft, Paxos, quorum | Distributed transactions | Architecture review |
| T10 Encoding | Binary, logic | Serialisation, schema | API design | ADRs |
| T11 Feedback | Recursion | Rate limiter, circuit breaker | Surge pricing, recs | Metrics → decisions |
| T12 Tradeoffs | Optimisation | CAP, SLO design | Every chapter | Every decision |